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Title: Insectivorous Plants

Author: Charles Darwin

Release date: May 1, 2004 [eBook #5765]
                Most recently updated: December 28, 2021

Language: English

Credits: Sue Asscher and David Widger


*** START OF THE PROJECT GUTENBERG EBOOK INSECTIVOROUS PLANTS ***




INSECTIVOROUS PLANTS

By Charles Darwin


CONTENTS

 DETAILED TABLE OF CONTENTS.
 INSECTIVOROUS PLANTS.
 CHAPTER I. DROSERA ROTUNDIFOLIA, OR THE COMMON SUN-DEW.
 CHAPTER II. THE MOVEMENTS OF THE TENTACLES FROM THE CONTACT OF SOLID BODIES.
 CHAPTER III. AGGREGATION OF THE PROTOPLASM WITHIN THE CELLS OF THE TENTACLES.
 CHAPTER IV. THE EFFECTS OF HEAT ON THE LEAVES. 
 CHAPTER V. THE EFFECTS OF NON-NITROGENOUS AND NITROGENOUS ORGANIC FLUIDS ON THE LEAVES.
 CHAPTER VI. THE DIGESTIVE POWER OF THE SECRETION OF DROSERA.
 CHAPTER VII. THE EFFECTS OF SALTS OF AMMONIA. 
 CHAPTER VIII. THE EFFECTS OF VARIOUS OTHER SALTS AND ACIDS ON THE LEAVES.
 CHAPTER IX. THE EFFECTS OF CERTAIN ALKALOID POISONS, OTHER SUBSTANCES AND VAPOURS.
 CHAPTER X. ON THE SENSITIVENESS OF THE LEAVES, AND ON THE LINES OF TRANSMISSION OF THE MOTOR IMPULSE.
 CHAPTER XI. RECAPITULATION OF THE CHIEF OBSERVATIONS ON DROSERA ROTUNDIFOLIA.
 CHAPTER XII. ON THE STRUCTURE AND MOVEMENTS OF SOME OTHER SPECIES OF DROSERA.
 CHAPTER XIII. DIONAEA MUSCIPULA.
 CHAPTER XIV. ALDROVANDA VESICULOSA.
 CHAPTER XV. DROSOPHYLLUM—RORIDULA—BYBLIS—GLANDULAR HAIRS OF OTHER PLANTS—CONCLUDING REMARKS ON THE DROSERACEÆ.
 CHAPTER XVI. PINGUICULA.
 CHAPTER XVII. UTRICULARIA.
 CHAPTER XVIII. UTRICULARIA (continued).
 CONCLUSION.
 INDEX.




DETAILED TABLE OF CONTENTS.


CHAPTER I.
DROSERA ROTUNDIFOLIA, OR THE COMMON SUN-DEW.
Number of insects captured—Description of the leaves and their
appendages or tentacles— Preliminary sketch of the action of the
various parts, and of the manner in which insects are captured—Duration
of the inflection of the tentacles—Nature of the secretion—Manner in
which insects are carried to the centre of the leaf—Evidence that the
glands have the power of absorption—Small size of the roots.

CHAPTER II.
THE MOVEMENTS OF THE TENTACLES FROM THE CONTACT OF SOLID BODIES.
Inflection of the exterior tentacles owing to the glands of the disc
being excited by repeated touches, or by objects left in contact with
them—Difference in the action of bodies yielding and not yielding
soluble nitrogenous matter—Inflection of the exterior tentacles
directly caused by objects left in contact with their glands—Periods of
commencing inflection and of subsequent re-expansion—Extreme minuteness
of the particles causing inflection—Action under water—Inflection of
the exterior tentacles when their glands are excited by repeated
touches—Falling drops of water do not cause inflection.

CHAPTER III.
AGGREGATION OF THE PROTOPLASM WITHIN THE CELLS OF THE TENTACLES.
Nature of the contents of the cells before aggregation—Various causes
which excite aggregation—The process commences within the glands and
travels down the tentacles— Description of the aggregated masses and of
their spontaneous movements—Currents of protoplasm along the walls of
the cells—Action of carbonate of ammonia—The granules in the protoplasm
which flows along the walls coalesce with the central masses—Minuteness
of the quantity of carbonate of ammonia causing aggregation—Action of
other salts of ammonia—Of other substances, organic fluids, &c.—Of
water—Of heat—Redissolution of the aggregated masses—Proximate causes
of the aggregation of the protoplasm—Summary and concluding
remarks—Supplementary observations on aggregation in the roots of
plants.

CHAPTER IV.
THE EFFECTS OF HEAT ON THE LEAVES.
Nature of the experiments—Effects of boiling water—Warm water causes
rapid inflection— Water at a higher temperature does not cause
immediate inflection, but does not kill the leaves, as shown by their
subsequent re-expansion and by the aggregation of the protoplasm— A
still higher temperature kills the leaves and coagulates the albuminous
contents of the glands.

CHAPTER V.
THE EFFECTS OF NON-NITROGENOUS AND NITROGENOUS ORGANIC FLUIDS ON THE
LEAVES.
Non-nitrogenous fluids—Solutions of gum arabic—Sugar—Starch—Diluted
alcohol—Olive oil— Infusion and decoction of tea—Nitrogenous
fluids—Milk—Urine—Liquid albumen—Infusion of raw meat—Impure
mucus—Saliva—Solution of isinglass—Difference in the action of these
two sets of fluids—Decoction of green peas—Decoction and infusion of
cabbage—Decoction of grass leaves.

CHAPTER VI.
THE DIGESTIVE POWER OF THE SECRETION OF DROSERA.
The secretion rendered acid by the direct and indirect excitement of
the glands—Nature of the acid—Digestible substances—Albumen, its
digestion arrested by alkalies, recommences by the addition of an
acid—Meat—Fibrin—Syntonin—Areolar tissue—Cartilage—Fibro-cartilage—
Bone—Enamel and dentine—Phosphate of lime—Fibrous basis of
bone—Gelatine—Chondrin— Milk, casein and
cheese—Gluten—Legumin—Pollen—Globulin—Haematin—Indigestible
substances—Epidermic productions—Fibro-elastic
tissue—Mucin—Pepsin—Urea—Chitine— Cellulose—Gun-cotton—Chlorophyll—Fat
and oil—Starch—Action of the secretion on living seeds—Summary and
concluding remarks.

CHAPTER VII.
THE EFFECTS OF SALTS OF AMMONIA.
Manner of performing the experiments—Action of distilled water in
comparison with the solutions—Carbonate of ammonia, absorbed by the
roots—The vapour absorbed by the glands—Drops on the disc—Minute drops
applied to separate glands—Leaves immersed in weak solutions—Minuteness
of the doses which induce aggregation of the protoplasm—Nitrate of
ammonia, analogous experiments with—Phosphate of ammonia, analogous
experiments with—Other salts of ammonia—Summary and concluding remarks
on the action of salts of ammonia.

CHAPTER VIII.
THE EFFECTS OF VARIOUS OTHER SALTS, AND ACIDS, ON THE LEAVES.
Salts of sodium, potassium, and other alkaline, earthy, and metallic
salts—Summary on the action of these salts—Various acids—Summary on
their action.

CHAPTER IX.
THE EFFECTS OF CERTAIN ALKALOID POISONS, OTHER SUBSTANCES AND VAPOURS.
Strychnine, salts of—Quinine, sulphate of, does not soon arrest the
movement of the protoplasm—Other salts of
quinine—Digitaline—Nicotine—Atropine—Veratrine— Colchicine—
Theine—Curare—Morphia—Hyoscyamus—Poison of the cobra, apparently
accelerates the movements of the protoplasm—Camphor, a powerful
stimulant, its vapour narcotic—Certain essential oils excite
movement—Glycerine—Water and certain solutions retard or prevent the
subsequent action of phosphate of ammonia—Alcohol innocuous, its vapour
narcotic and poisonous—Chloroform, sulphuric and nitric ether, their
stimulant, poisonous, and narcotic power—Carbonic acid narcotic, not
quickly poisonous—Concluding remarks.

CHAPTER X.
ON THE SENSITIVENESS OF THE LEAVES, AND ON THE LINES OF TRANSMISSION OF
THE MOTOR IMPULSE.
Glands and summits of the tentacles alone sensitive—Transmission of the
motor impulse down the pedicels of the tentacles, and across the blade
of the leaf—Aggregation of the protoplasm, a reflex action—First
discharge of the motor impulse sudden—Direction of the movements of the
tentacles—Motor impulse transmitted through the cellular tissue—
Mechanism of the movements—Nature of the motor impulse—Re-expansion of
the tentacles.

CHAPTER XI.
RECAPITULATION OF THE CHIEF OBSERVATIONS ON DROSERA ROTUNDIFOLIA.

CHAPTER XII.
ON THE STRUCTURE AND MOVEMENTS OF SOME OTHER SPECIES OF DROSERA.
Drosera anglica—Drosera intermedia—Drosera capensis—Drosera
spathulata—Drosera filiformis—Drosera binata—Concluding remarks.

CHAPTER XIII.
DIONAEA MUSCIPULA.
Structure of the leaves—Sensitiveness of the filaments—Rapid movement
of the lobes caused by irritation of the filaments—Glands, their power
of secretion—Slow movement caused by the absorption of animal
matter—Evidence of absorption from the aggregated condition of the
glands—Digestive power of the secretion—Action of chloroform, ether,
and hydrocyanic acid—The manner in which insects are captured—Use of
the marginal spikes—Kinds of insects captured—The transmission of the
motor impulse and mechanism of the movements— Re-expansion of the
lobes.

CHAPTER XIV.
ALDROVANDA VESICULOSA.
Captures crustaceans—Structure of the leaves in comparison with those
of Dionaea—Absorption by the glands, by the quadrifid processes, and
points on the infolded margins—Aldrovanda vesiculosa, var.
australis—Captures prey—Absorption of animal matter—Aldrovanda
vesiculosa, var. verticillata—Concluding remarks.

CHAPTER XV.
DROSOPHYLLUM—RORIDULA—BYBLIS—GLANDULAR HAIRS OF OTHER PLANTS—
CONCLUDING REMARKS ON THE DROSERACEÆ.
Drosophyllum—Structure of leaves—Nature of the secretion—Manner of
catching insects— Power of absorption—Digestion of animal
substances—Summary on Drosophyllum—Roridula—Byblis—Glandular hairs of
other plants, their power of absorption—Saxifraga—Primula—
Pelargonium—Erica—Mirabilis—Nicotiana—Summary on glandular
hairs—Concluding remarks on the Droseraceae.

CHAPTER XVI.
PINGUICULA.
Pinguicula vulgaris—Structure of leaves—Number of insects and other
objects caught—Movement of the margins of the leaves—Uses of this
movement—Secretion, digestion, and absorption—Action of the secretion
on various animal and vegetable substances—The effects of substances
not containing soluble nitrogenous matter on the glands—Pinguicula
grandiflora—Pinguicula lusitanica, catches insects—Movement of the
leaves, secretion and digestion.

CHAPTER XVII.
UTRICULARIA.
Utricularia neglecta—Structure of the bladder—The uses of the several
parts—Number of imprisoned animals—Manner of capture—The bladders
cannot digest animal matter, but absorb the products of its
decay—Experiments on the absorption of certain fluids by the quadrifid
processes—Absorption by the glands—Summary of the observation on
absorption— Development of the bladders—Utricularia
vulgaris—Utricularia minor—Utricularia clandestina.

CHAPTER XVIII.
UTRICULARIA (continued).
Utricularia montana—Description of the bladders on the subterranean
rhizomes—Prey captured by the bladders of plants under culture and in a
state of nature—Absorption by the quadrifid processes and glands—Tubers
serving as reservoirs for water—Various other species of
Utricularia—Polypompholyx—Genlisea, different nature of the trap for
capturing prey— Diversified methods by which plants are nourished.




INSECTIVOROUS PLANTS.




CHAPTER I.
DROSERA ROTUNDIFOLIA, OR THE COMMON SUN-DEW.


Number of insects captured—Description of the leaves and their
appendages or tentacles— Preliminary sketch of the action of the
various parts, and of the manner in which insects are captured—Duration
of the inflection of the tentacles—Nature of the secretion—Manner in
which insects are carried to the centre of the leaf—Evidence that the
glands have the power of absorption—Small size of the roots.


During the summer of 1860, I was surprised by finding how large a
number of insects were caught by the leaves of the common sun-dew
(Drosera rotundifolia) on a heath in Sussex. I had heard that insects
were thus caught, but knew nothing further on the subject.* I

* As Dr. Nitschke has given (‘Bot. Zeitung,’ 1860, p. 229) the
bibliography of Drosera, I need not here go into details. Most of the
notices published before 1860 are brief and unimportant. The oldest
paper seems to have been one of the most valuable, namely, by Dr. Roth,
in 1782. There is also an interesting though short account of the
habits of Drosera by Dr. Milde, in the ‘Bot. Zeitung,’ 1852, p. 540. In
1855, in the ‘Annales des Sc. nat. bot.’ tom. iii. pp. 297 and 304, MM.
Groenland and Trcul each published papers, with figures, on the
structure of the leaves; but M. Trcul went so far as to doubt whether
they possessed any power of movement. Dr. Nitschke’s papers in the
‘Bot. Zeitung’ for 1860 and 1861 are by far the most important ones
which have been published, both on the habits and structure of this
plant; and I shall frequently have occasion to quote from them. His
discussions on several points, for instance on the transmission of an
excitement from one part of the leaf to another, are excellent. On
December 11, 1862, Mr. J. Scott read a paper before the Botanical
Society of Edinburgh, [[page 2]] which was published in the ‘Gardeners’
Chronicle,’ 1863, p. 30. Mr. Scott shows that gentle irritation of the
hairs, as well as insects placed on the disc of the leaf, cause the
hairs to bend inwards. Mr. A.W. Bennett also gave another interesting
account of the movements of the leaves before the British Association
for 1873. In this same year Dr. Warming published an essay, in which he
describes the structure of the so-called hairs, entitled, “Sur la
Diffrence entre les Trichomes,” &c., extracted from the proceedings of
the Soc. d’Hist. Nat. de Copenhague. I shall also have occasion
hereafter to refer to a paper by Mrs. Treat, of New Jersey, on some
American species of Drosera. Dr. Burdon Sanderson delivered a lecture
on Dionaea, before the Royal Institution published in ‘Nature,’ June
14, 1874, in which a short account of my observations on the power of
true digestion possessed by Drosera and Dionaea first appeared. Prof.
Asa Gray has done good service by calling attention to Drosera, and to
other plants having similar habits, in ‘The Nation’ (1874, pp. 261 and
232), and in other publications. Dr. Hooker, also, in his important
address on Carnivorous Plants (Brit. Assoc., Belfast, 1874), has given
a history of the subject. [page 2]


gathered by chance a dozen plants, bearing fifty-six fully expanded
leaves, and on thirty-one of these dead insects or remnants of them
adhered; and, no doubt, many more would have been caught afterwards by
these same leaves, and still more by those as yet not expanded. On one
plant all six leaves had caught their prey; and on several plants very
many leaves had caught more than a single insect. On one large leaf I
found the remains of thirteen distinct insects. Flies (Diptera) are
captured much oftener than other insects. The largest kind which I have
seen caught was a small butterfly (Caenonympha pamphilus); but the Rev.
H.M. Wilkinson informs me that he found a large living dragon-fly with
its body firmly held by two leaves. As this plant is extremely common
in some districts, the number of insects thus annually slaughtered must
be prodigious. Many plants cause the death of insects, for instance the
sticky buds of the horse-chestnut (Aesculus hippocastanum), without
thereby receiving, as far as we can perceive, any advantage; but it was
soon evident that Drosera was [page 3] excellently adapted for the
special purpose of catching insects, so that the subject seemed well
worthy of investigation.

The results have proved highly remarkable; the more important ones
being—firstly, the extraordinary

FIG. 1.* (Drosera rotundifolia.) Leaf viewed from above; enlarged four
times.

sensitiveness of the glands to slight pressure and to minute doses of
certain nitrogenous fluids, as shown by the movements of the so-called
hairs or tentacles;

* The drawings of Drosera and Dionaea, given in this work, were made
for me by my son George Darwin; those of Aldrovanda, and of the several
species of Utricularia, by my son Francis. They have been excellently
reproduced on wood by Mr. Cooper, 188 Strand. [page 4]


secondly, the power possessed by the leaves of rendering soluble or
digesting nitrogenous substances, and of afterwards absorbing them;
thirdly, the changes which take place within the cells of the
tentacles, when the glands are excited in various ways.

It is necessary, in the first place, to describe briefly the plant. It
bears from two or three to five or six leaves, generally extended more
or less horizontally, but sometimes standing vertically upwards. The
shape and general appearance of a leaf is shown, as seen from above, in
fig. 1, and as seen laterally, in fig. 2. The leaves are commonly a
little broader than long,

FIG. 2. (Drosera rotundifolia.) Old leaf viewed laterally; enlarged
about five times.

but this was not the case in the one here figured. The whole upper
surface is covered with gland-bearing filaments, or tentacles, as I
shall call them, from their manner of acting. The glands were counted
on thirty-one leaves, but many of these were of unusually large size,
and the average number was 192; the greatest number being 260, and the
least 130. The glands are each surrounded by large drops of extremely
viscid secretion, which, glittering in the sun, have given rise to the
plant’s poetical name of the sun-dew.

[The tentacles on the central part of the leaf or disc are short and
stand upright, and their pedicels are green. Towards the margin they
become longer and longer and more inclined [page 5] outwards, with
their pedicels of a purple colour. Those on the extreme margin project
in the same plane with the leaf, or more commonly (see fig. 2) are
considerably reflexed. A few tentacles spring from the base of the
footstalk or petiole, and these are the longest of all, being sometimes
nearly 1/4 of an inch in length. On a leaf bearing altogether 252
tentacles, the short ones on the disc, having green pedicels, were in
number to the longer submarginal and marginal tentacles, having purple
pedicels, as nine to sixteen.

A tentacle consists of a thin, straight, hair-like pedicel, carrying a
gland on the summit. The pedicel is somewhat flattened, and is formed
of several rows of elongated cells, filled with purple fluid or
granular matter.* There is, however, a narrow zone close beneath the
glands of the longer tentacles, and a broader zone near their bases, of
a green tint. Spiral vessels, accompanied by simple vascular tissue,
branch off from the vascular bundles in the blade of the leaf, and run
up all the tentacles into the glands.

Several eminent physiologists have discussed the homological nature of
these appendages or tentacles, that is, whether they ought to be
considered as hairs (trichomes) or prolongations of the leaf. Nitschke
has shown that they include all the elements proper to the blade of a
leaf; and the fact of their including vascular tissue was formerly
thought to prove that they were prolongations of the leaf, but it is
now known that vessels sometimes enter true hairs.** The power of
movement which they possess is a strong argument against their being
viewed as hairs. The conclusion which seems to me the most probable
will be given in Chap. XV., namely that they existed primordially as
glandular hairs, or mere epidermic formations, and that their upper
part should still be so considered; but that their lower

* According to Nitschke (‘Bot. Zeitung,’ 1861, p. 224) the purple fluid
results from the metamorphosis of chlorophyll. Mr. Sorby examined the
colouring matter with the spectroscope, and informs me that it consists
of the commonest species of erythrophyll, “which is often met with in
leaves with low vitality, and in parts, like the petioles, which carry
on leaf-functions in a very imperfect manner. All that can be said,
therefore, is that the hairs (or tentacles) are coloured like parts of
a leaf which do not fulfil their proper office.”


** Dr. Nitschke has discussed this subject in ‘Bot. Zeitung,’ 1861, p.
241 &c. See also Dr. Warming (‘Sur la Diffrence entre les Trichomes’
&c., 1873), who gives references to various publications. See also
Groenland and Trcul ‘Annal. des Sc. nat. bot.’ (4th series), tom. iii.
1855, pp. 297 and 303. [page 6]


part, which alone is capable of movement, consists of a prolongation of
the leaf; the spiral vessels being extended from this to the uppermost
part. We shall hereafter see that the terminal tentacles of the divided
leaves of Roridula are still in an intermediate condition.

The glands, with the exception of those borne by the extreme

FIG. 3. (Drosera rotundifolia.) Longitudinal section of a gland;
greatly magnified. From Dr. Warming.

marginal tentacles, are oval, and of nearly uniform size, viz. about
4/500 of an inch in length. Their structure is remarkable, and their
functions complex, for they secrete, absorb, and are acted on by
various stimulants. They consist of an outer layer of small polygonal
cells, containing purple granular matter or fluid, and with the walls
thicker than those of the pedicels. [page 7] Within this layer of cells
there is an inner one of differently shaped ones, likewise filled with
purple fluid, but of a slightly different tint, and differently
affected by chloride of gold. These two layers are sometimes well seen
when a gland has been crushed or boiled in caustic potash. According to
Dr. Warming, there is still another layer of much more elongated cells,
as shown in the accompanying section (fig. 3) copied from his work; but
these cells were not seen by Nitschke, nor by me. In the centre there
is a group of elongated, cylindrical cells of unequal lengths, bluntly
pointed at their upper ends, truncated or rounded at their lower ends,
closely pressed together, and remarkable from being surrounded by a
spiral line, which can be separated as a distinct fibre.

These latter cells are filled with limpid fluid, which after long
immersion in alcohol deposits much brown matter. I presume that they
are actually connected with the spiral vessels which run up the
tentacles, for on several occasions the latter were seen to divide into
two or three excessively thin branches, which could be traced close up
to the spiriferous cells. Their development has been described by Dr.
Warming. Cells of the same kind have been observed in other plants, as
I hear from Dr. Hooker, and were seen by me in the margins of the
leaves of Pinguicula. Whatever their function may be, they are not
necessary for the secretion of a digestive fluid, or for absorption, or
for the communication of a motor impulse to other parts of the leaf, as
we may infer from the structure of the glands in some other genera of
the Droseraceae.

The extreme marginal tentacles differ slightly from the others. Their
bases are broader, and besides their own vessels, they receive a fine
branch from those which enter the tentacles on each side. Their glands
are much elongated, and lie embedded on the upper surface of the
pedicel, instead of standing at the apex. In other respects they do not
differ essentially from the oval ones, and in one specimen I found
every possible transition between the two states. In another specimen
there were no long-headed glands. These marginal tentacles lose their
irritability earlier than the others; and when a stimulus is applied to
the centre of the leaf, they are excited into action after the others.
When cut-off leaves are immersed in water, they alone often become
inflected.

The purple fluid or granular matter which fills the cells of the glands
differs to a certain extent from that within the cells of the pedicels.
For when a leaf is placed in hot water or in certain acids, the glands
become quite white and opaque, whereas [page 8] the cells of the
pedicels are rendered of a bright red, with the exception of those
close beneath the glands. These latter cells lose their pale red tint;
and the green matter which they, as well as the basal cells, contain,
becomes of a brighter green. The petioles bear many multicellular
hairs, some of which near the blade are surmounted, according to
Nitschke, by a few rounded cells, which appear to be rudimentary
glands. Both surfaces of the leaf, the pedicels of the tentacles,
especially the lower sides of the outer ones, and the petioles, are
studded with minute papillae (hairs or trichomes), having a conical
basis, and bearing on their summits two, and occasionally three or even
four, rounded cells, containing much protoplasm. These papillae are
generally colourless, but sometimes include a little purple fluid. They
vary in development, and graduate, as Nitschke* states, and as I
repeatedly observed, into the long multicellular hairs. The latter, as
well as the papillae, are probably rudiments of formerly existing
tentacles.

I may here add, in order not to recur to the papillae, that they do not
secrete, but are easily permeated by various fluids: thus when living
or dead leaves are immersed in a solution of one part of chloride of
gold, or of nitrate of silver, to 437 of water, they are quickly
blackened, and the discoloration soon spreads to the surrounding
tissue. The long multicellular hairs are not so quickly affected. After
a leaf had been left in a weak infusion of raw meat for 10 hours, the
cells of the papillae had evidently absorbed animal matter, for instead
of limpid fluid they now contained small aggregated masses of
protoplasm, which slowly and incessantly changed their forms. A similar
result followed from an immersion of only 15 minutes in a solution of
one part of carbonate of ammonia to 218 of water, and the adjoining
cells of the tentacles, on which the papillae were seated, now likewise
contained aggregated masses of protoplasm. We may therefore conclude
that when a leaf has closely clasped a captured insect in the manner
immediately to be described, the papillae, which project from the upper
surface of the leaf and of the tentacles, probably absorb some of the
animal matter dissolved in the secretion; but this cannot be the case
with the papillae on the backs of the leaves or on the petioles.]

* Nitschke has elaborately described and figured these papillae, ‘Bot.
Zeitung,’ 1861, pp. 234, 253, 254. [page 9]


_Preliminary Sketch of the Action of the several Parts, and of the
Manner in which Insects are Captured._


If a small organic or inorganic object be placed on the glands in the
centre of a leaf, these transmit a motor impulse to the marginal
tentacles. The nearer ones are first affected and slowly bend towards
the centre, and then those farther off, until at last all become
closely inflected over the object. This takes place in from one hour to
four or five or more hours. The difference in the time required depends
on many circumstances; namely on the size of the object and on its
nature, that is, whether it contains soluble matter of the proper kind;
on the vigour and age of the leaf; whether it has lately been in
action; and, according to Nitschke,* on the temperature of the day, as
likewise seemed to me to be the case. A living insect is a more
efficient object than a dead one, as in struggling it presses against
the glands of many tentacles. An insect, such as a fly, with thin
integuments, through which animal matter in solution can readily pass
into the surrounding dense secretion, is more efficient in causing
prolonged inflection than an insect with a thick coat, such as a
beetle. The inflection of the tentacles takes place indifferently in
the light and darkness; and the plant is not subject to any nocturnal
movement of so-called sleep.

If the glands on the disc are repeatedly touched or brushed, although
no object is left on them, the marginal tentacles curve inwards. So
again, if drops of various fluids, for instance of saliva or of a
solution of any salt of ammonia, are placed on the central glands, the
same result quickly follows, sometimes in under half an hour.

* ‘Bot. Zeitung,’ 1860, p. 246. [page 10]


The tentacles in the act of inflection sweep through a wide space; thus
a marginal tentacle, extended in the same plane with the blade, moves
through an angle of 180o; and I have seen the much reflected tentacles
of a leaf which stood upright move through an angle of not less than
270o. The bending part is almost confined to a short space near the
base; but a rather larger portion of the elongated exterior tentacles

FIG. 4. (Drosera rotundifolia.) Leaf (enlarged) with all the tentacles
closely inflected, from immersion in a solution of phosphate of ammonia
(one part to 87,500 of water.)

FIG. 5. (Drosera rotundifolia.) Leaf (enlarged) with the tentacles on
one side inflected over a bit of meat placed on the disc.

becomes slightly incurved; the distal half in all cases remaining
straight. The short tentacles in the centre of the disc when directly
excited, do not become inflected; but they are capable of inflection if
excited by a motor impulse received from other glands at a distance.
Thus, if a leaf is immersed in an infusion of raw meat, or in a weak
solution of ammonia (if the [page 11] solution is at all strong, the
leaf is paralysed), all the exterior tentacles bend inwards (see fig.
4), excepting those near the centre, which remain upright; but these
bend towards any exciting object placed on one side of the disc, as
shown in fig. 5. The glands in fig. 4 may be seen to form a dark ring
round the centre; and this follows from the exterior tentacles
increasing in length in due proportion, as they stand nearer to the
circumference.

The kind of inflection which the tentacles undergo is best shown when
the gland of one of the long exterior

FIG. 6. (Drosera rotundifolia.) Diagram showing one of the exterior
tentacles closely inflected; the two adjoining ones in their ordinary
position.)

tentacles is in any way excited; for the surrounding ones remain
unaffected. In the accompanying outline (fig. 6) we see one tentacle,
on which a particle of meat had been placed, thus bent towards the
centre of the leaf, with two others retaining their original position.
A gland may be excited by being simply touched three or four times, or
by prolonged contact with organic or inorganic objects, and various
fluids. I have distinctly seen, through a lens, a tentacle beginning to
bend in ten seconds, after an object had been [page 12] placed on its
gland; and I have often seen strongly pronounced inflection in under
one minute. It is surprising how minute a particle of any substance,
such as a bit of thread or hair or splinter of glass, if placed in
actual contact with the surface of a gland, suffices to cause the
tentacle to bend. If the object, which has been carried by this
movement to the centre, be not very small, or if it contains soluble
nitrogenous matter, it acts on the central glands; and these transmit a
motor impulse to the exterior tentacles, causing them to bend inwards.

Not only the tentacles, but the blade of the leaf often, but by no
means always, becomes much incurved, when any strongly exciting
substance or fluid is placed on the disc. Drops of milk and of a
solution of nitrate of ammonia or soda are particularly apt to produce
this effect. The blade is thus converted into a little cup. The manner
in which it bends varies greatly. Sometimes the apex alone, sometimes
one side, and sometimes both sides, become incurved. For instance, I
placed bits of hard-boiled egg on three leaves; one had the apex bent
towards the base; the second had both distal margins much incurved, so
that it became almost triangular in outline, and this perhaps is the
commonest case; whilst the third blade was not at all affected, though
the tentacles were as closely inflected as in the two previous cases.
The whole blade also generally rises or bends upwards, and thus forms a
smaller angle with the footstalk than it did before. This appears at
first sight a distinct kind of movement, but it results from the
incurvation of that part of the margin which is attached to the
footstalk, causing the blade, as a whole, to curve or move upwards.

The length of time during which the tentacles as [page 13] well as the
blade remain inflected over an object placed on the disc, depends on
various circumstances; namely on the vigour and age of the leaf, and,
according to Dr. Nitschke, on the temperature, for during cold weather
when the leaves are inactive, they re-expand at an earlier period than
when the weather is warm. But the nature of the object is by far the
most important circumstance; I have repeatedly found that the tentacles
remain clasped for a much longer average time over objects which yield
soluble nitrogenous matter than over those, whether organic or
inorganic, which yield no such matter. After a period varying from one
to seven days, the tentacles and blade re-expand, and are then ready to
act again. I have seen the same leaf inflected three successive times
over insects placed on the disc; and it would probably have acted a
greater number of times.

The secretion from the glands is extremely viscid, so that it can be
drawn out into long threads. It appears colourless, but stains little
balls of paper pale pink. An object of any kind placed on a gland
always causes it, as I believe, to secrete more freely; but the mere
presence of the object renders this difficult to ascertain. In some
cases, however, the effect was strongly marked, as when particles of
sugar were added; but the result in this case is probably due merely to
exosmose. Particles of carbonate and phosphate of ammonia and of some
other salts, for instance sulphate of zinc, likewise increase the
secretion. Immersion in a solution of one part of chloride of gold, or
of some other salts, to 437 of water, excites the glands to largely
increased secretion; on the other hand, tartrate of antimony produces
no such effect. Immersion in many acids (of the strength of one part to
437 of water) likewise causes a wonderful amount of [page 14]
secretion, so that when the leaves are lifted out, long ropes of
extremely viscid fluid hang from them. Some acids, on the other hand,
do not act in this manner. Increased secretion is not necessarily
dependent on the inflection of the tentacle, for particles of sugar and
of sulphate of zinc cause no movement.

It is a much more remarkable fact that when an object, such as a bit of
meat or an insect, is placed on the disc of a leaf, as soon as the
surrounding tentacles become considerably inflected, their glands pour
forth an increased amount of secretion. I ascertained this by selecting
leaves with equal-sized drops on the two sides, and by placing bits of
meat on one side of the disc; and as soon as the tentacles on this side
became much inflected, but before the glands touched the meat, the
drops of secretion became larger. This was repeatedly observed, but a
record was kept of only thirteen cases, in nine of which increased
secretion was plainly observed; the four failures being due either to
the leaves being rather torpid, or to the bits of meat being too small
to cause much inflection. We must therefore conclude that the central
glands, when strongly excited, transmit some influence to the glands of
the circumferential tentacles, causing them to secrete more copiously.

It is a still more important fact (as we shall see more fully when we
treat of the digestive power of the secretion) that when the tentacles
become inflected, owing to the central glands having been stimulated
mechanically, or by contact with animal matter, the secretion not only
increases in quantity, but changes its nature and becomes acid; and
this occurs before the glands have touched the object on the centre of
the leaf. This acid is of a different nature from that contained in the
tissue of the leaves. As long as the [page 15] tentacles remain closely
inflected, the glands continue to secrete, and the secretion is acid;
so that, if neutralised by carbonate of soda, it again becomes acid
after a few hours. I have observed the same leaf with the tentacles
closely inflected over rather indigestible substances, such as
chemically prepared casein, pouring forth acid secretion for eight
successive days, and over bits of bone for ten successive days.

The secretion seems to possess, like the gastric juice of the higher
animals, some antiseptic power. During very warm weather I placed close
together two equal-sized bits of raw meat, one on a leaf of the
Drosera, and the other surrounded by wet moss. They were thus left for
48 hrs., and then examined. The bit on the moss swarmed with infusoria,
and was so much decayed that the transverse striae on the muscular
fibres could no longer be clearly distinguished; whilst the bit on the
leaf, which was bathed by the secretion, was free from infusoria, and
its striae were perfectly distinct in the central and undissolved
portion. In like manner small cubes of albumen and cheese placed on wet
moss became threaded with filaments of mould, and had their surfaces
slightly discoloured and disintegrated; whilst those on the leaves of
Drosera remained clean, the albumen being changed into transparent
fluid.

As soon as tentacles, which have remained closely inflected during
several days over an object, begin to re-expand, their glands secrete
less freely, or cease to secrete, and are left dry. In this state they
are covered with a film of whitish, semi-fibrous matter, which was held
in solution by the secretion. The drying of the glands during the act
of re-expansion is of some little service to the plant; for I have
often observed that objects adhering to the leaves [page 16] could then
be blown away by a breath of air; the leaves being thus left
unencumbered and free for future action. Nevertheless, it often happens
that all the glands do not become completely dry; and in this case
delicate objects, such as fragile insects, are sometimes torn by the
re-expansion of the tentacles into fragments, which remain scattered
all over the leaf. After the re-expansion is complete, the glands
quickly begin to re-secrete, and as soon as full-sized drops are
formed, the tentacles are ready to clasp a new object.

When an insect alights on the central disc, it is instantly entangled
by the viscid secretion, and the surrounding tentacles after a time
begin to bend, and ultimately clasp it on all sides. Insects are
generally killed, according to Dr. Nitschke, in about a quarter of an
hour, owing to their tracheae being closed by the secretion. If an
insect adheres to only a few of the glands of the exterior tentacles,
these soon become inflected and carry their prey to the tentacles next
succeeding them inwards; these then bend inwards, and so onwards; until
the insect is ultimately carried by a curious sort of rolling movement
to the centre of the leaf. Then, after an interval, the tentacles on
all sides become inflected and bathe their prey with their secretion,
in the same manner as if the insect had first alighted on the central
disc. It is surprising how minute an insect suffices to cause this
action: for instance, I have seen one of the smallest species of gnats
(Culex), which had just settled with its excessively delicate feet on
the glands of the outermost tentacles, and these were already beginning
to curve inwards, though not a single gland had as yet touched the body
of the insect. Had I not interfered, this minute gnat would [page 17]
assuredly have been carried to the centre of the leaf and been securely
clasped on all sides. We shall hereafter see what excessively small
doses of certain organic fluids and saline solutions cause strongly
marked inflection.

Whether insects alight on the leaves by mere chance, as a resting
place, or are attracted by the odour of the secretion, I know not. I
suspect from the number of insects caught by the English species of
Drosera, and from what I have observed with some exotic species kept in
my greenhouse, that the odour is attractive. In this latter case the
leaves may be compared with a baited trap; in the former case with a
trap laid in a run frequented by game, but without any bait.

That the glands possess the power of absorption, is shown by their
almost instantaneously becoming dark-coloured when given a minute
quantity of carbonate of ammonia; the change of colour being chiefly or
exclusively due to the rapid aggregation of their contents. When
certain other fluids are added, they become pale-coloured. Their power
of absorption is, however, best shown by the widely different results
which follow, from placing drops of various nitrogenous and
non-nitrogenous fluids of the same density on the glands of the disc,
or on a single marginal gland; and likewise by the very different
lengths of time during which the tentacles remain inflected over
objects, which yield or do not yield soluble nitrogenous matter. This
same conclusion might indeed have been inferred from the structure and
movements of the leaves, which are so admirably adapted for capturing
insects.

The absorption of animal matter from captured insects explains how
Drosera can flourish in extremely poor peaty soil,—in some cases where
nothing but [page 18] sphagnum moss grows, and mosses depend altogether
on the atmosphere for their nourishment. Although the leaves at a hasty
glance do not appear green, owing to the purple colour of the
tentacles, yet the upper and lower surfaces of the blade, the pedicels
of the central tentacles, and the petioles contain chlorophyll, so
that, no doubt, the plant obtains and assimilates carbonic acid from
the air. Nevertheless, considering the nature of the soil where it
grows, the supply of nitrogen would be extremely limited, or quite
deficient, unless the plant had the power of obtaining this important
element from captured insects. We can thus understand how it is that
the roots are so poorly developed. These usually consist of only two or
three slightly divided branches, from half to one inch in length,
furnished with absorbent hairs. It appears, therefore, that the roots
serve only to imbibe water; though, no doubt, they would absorb
nutritious matter if present in the soil; for as we shall hereafter
see, they absorb a weak solution of carbonate of ammonia. A plant of
Drosera, with the edges of its leaves curled inwards, so as to form a
temporary stomach, with the glands of the closely inflected tentacles
pouring forth their acid secretion, which dissolves animal matter,
afterwards to be absorbed, may be said to feed like an animal. But,
differently from an animal, it drinks by means of its roots; and it
must drink largely, so as to retain many drops of viscid fluid round
the glands, sometimes as many as 260, exposed during the whole day to a
glaring sun. [page 19]




CHAPTER II.
THE MOVEMENTS OF THE TENTACLES FROM THE CONTACT OF SOLID BODIES.


Inflection of the exterior tentacles owing to the glands of the disc
being excited by repeated touches, or by objects left in contact with
them—Difference in the action of bodies yielding and not yielding
soluble nitrogenous matter—Inflection of the exterior tentacles
directly caused by objects left in contact with their glands—Periods of
commencing inflection and of subsequent re-expansion—Extreme minuteness
of the particles causing inflection—Action under water—Inflection of
the exterior tentacles when their glands are excited by repeated
touches—Falling drops of water do not cause inflection.


I will give in this and the following chapters some of the many
experiments made, which best illustrate the manner and rate of movement
of the tentacles, when excited in various ways. The glands alone in all
ordinary cases are susceptible to excitement. When excited, they do not
themselves move or change form, but transmit a motor impulse to the
bending part of their own and adjoining tentacles, and are thus carried
towards the centre of the leaf. Strictly speaking, the glands ought to
be called irritable, as the term sensitive generally implies
consciousness; but no one supposes that the Sensitive-plant is
conscious, and as I have found the term convenient, I shall use it
without scruple. I will commence with the movements of the exterior
tentacles, when indirectly excited by stimulants applied to the glands
of the short tentacles on the disc. The exterior tentacles may be said
in this case to be indirectly excited, because their own glands are not
directly acted on. The stimulus proceeding from the glands of the disc
acts on the bending part of the [page 20] exterior tentacles, near
their bases, and does not (as will hereafter be proved) first travel up
the pedicels to the glands, to be then reflected back to the bending
place. Nevertheless, some influence does travel up to the glands,
causing them to secrete more copiously, and the secretion to become
acid. This latter fact is, I believe, quite new in the physiology of
plants; it has indeed only recently been established that in the animal
kingdom an influence can be transmitted along the nerves to glands,
modifying their power of secretion, independently of the state of the
blood-vessels.

The Inflection of the Exterior Tentacles from the Glands of the Disc
being excited by Repeated Touches, or by Objects left in Contact with
them.

The central glands of a leaf were irritated with a small stiff
camel-hair brush, and in 70 m. (minutes) several of the outer tentacles
were inflected; in 5 hrs. (hours) all the sub-marginal tentacles were
inflected; next morning after an interval of about 22 hrs. they were
fully re-expanded. In all the following cases the period is reckoned
from the time of first irritation. Another leaf treated in the same
manner had a few tentacles inflected in 20 m.; in 4 hrs. all the
submarginal and some of the extreme marginal tentacles, as well as the
edge of the leaf itself, were inflected; in 17 hrs. they had recovered
their proper, expanded position. I then put a dead fly in the centre of
the last-mentioned leaf, and next morning it was closely clasped; five
days afterwards the leaf re-expanded, and the tentacles, with their
glands surrounded by secretion, were ready to act again.

Particles of meat, dead flies, bits of paper, wood, dried moss, sponge,
cinders, glass, &c., were repeatedly [page 21] placed on leaves, and
these objects were well embraced in various periods from one hr. to as
long as 24 hrs., and set free again, with the leaf fully re-expanded,
in from one or two, to seven or even ten days, according to the nature
of the object. On a leaf which had naturally caught two flies, and
therefore had already closed and reopened either once or more probably
twice, I put a fresh fly: in 7 hrs. it was moderately, and in 21 hrs.
thoroughly well, clasped, with the edges of the leaf inflected. In two
days and a half the leaf had nearly re-expanded; as the exciting object
was an insect, this unusually short period of inflection was, no doubt,
due to the leaf having recently been in action. Allowing this same leaf
to rest for only a single day, I put on another fly, and it again
closed, but now very slowly; nevertheless, in less than two days it
succeeded in thoroughly clasping the fly.

When a small object is placed on the glands of the disc, on one side of
a leaf, as near as possible to its circumference, the tentacles on this
side are first affected, those on the opposite side much later, or, as
often occurred, not at all. This was repeatedly proved by trials with
bits of meat; but I will here give only the case of a minute fly,
naturally caught and still alive, which I found adhering by its
delicate feet to the glands on the extreme left side of the central
disc. The marginal tentacles on this side closed inwards and killed the
fly, and after a time the edge of the leaf on this side also became
inflected, and thus remained for several days, whilst neither the
tentacles nor the edge on the opposite side were in the least affected.

If young and active leaves are selected, inorganic particles not larger
than the head of a small pin, placed on the central glands, sometimes
cause the [page 22] outer tentacles to bend inwards. But this follows
much more surely and quickly, if the object contains nitrogenous matter
which can be dissolved by the secretion. On one occasion I observed the
following unusual circumstance. Small bits of raw meat (which acts more
energetically than any other substance), of paper, dried moss, and of
the quill of a pen were placed on several leaves, and they were all
embraced equally well in about 2 hrs. On other occasions the
above-named substances, or more commonly particles of glass,
coal-cinder (taken from the fire), stone, gold-leaf, dried grass, cork,
blotting-paper, cotton-wool, and hair rolled up into little balls, were
used, and these substances, though they were sometimes well embraced,
often caused no movement whatever in the outer tentacles, or an
extremely slight and slow movement. Yet these same leaves were proved
to be in an active condition, as they were excited to move by
substances yielding soluble nitrogenous matter, such as bits of raw or
roast meat, the yolk or white of boiled eggs, fragments of insects of
all orders, spiders, &c. I will give only two instances. Minute flies
were placed on the discs of several leaves, and on others balls of
paper, bits of moss and quill of about the same size as the flies, and
the latter were well embraced in a few hours; whereas after 25 hrs.
only a very few tentacles were inflected over the other objects. The
bits of paper, moss, and quill were then removed from these leaves, and
bits of raw meat placed on them; and now all the tentacles were soon
energetically inflected.

Again, particles of coal-cinder (weighing rather more than the flies
used in the last experiment) were placed on the centres of three
leaves: after an interval of 19 hrs. one of the particles was tolerably
well embraced; [page 23] a second by a very few tentacles; and a third
by none. I then removed the particles from the two latter leaves, and
put on them recently killed flies. These were fairly well embraced in 7
1/2 hrs. and thoroughly after 20 1/2 hrs.; the tentacles remaining
inflected for many subsequent days. On the other hand, the one leaf
which had in the course of 19 hrs. embraced the bit of cinder
moderately well, and to which no fly was given, after an additional 33
hrs. (i.e. in 52 hrs. from the time when the cinder was put on) was
completely re-expanded and ready to act again.

From these and numerous other experiments not worth giving, it is
certain that inorganic substances, or such organic substances as are
not attacked by the secretion, act much less quickly and efficiently
than organic substances yielding soluble matter which is absorbed.
Moreover, I have met with very few exceptions to the rule, and these
exceptions apparently depended on the leaf having been too recently in
action, that the tentacles remain clasped for a much longer time over
organic bodies of the nature just specified than over those which are
not acted on by the secretion, or over inorganic objects.*

* Owing to the extraordinary belief held by M. Ziegler (‘Comptes
rendus,’ May 1872, p. 122), that albuminous substances, if held for a
moment between the fingers, acquire the property of making the
tentacles of Drosera contract, whereas, if not thus held, they have no
such power, I tried some experiments with great care, but the results
did not confirm this belief. Red-hot cinders were taken out of the
fire, and bits of glass, cotton-thread, blotting paper and thin slices
of cork were immersed in boiling water; and particles were then placed
(every instrument with which they were touched having been previously
immersed in boiling water) on the glands of several leaves, and they
acted in exactly the same manner as other particles, which had been
purposely handled for some time. Bits of a boiled egg, cut with a knife
which had been washed in boiling water, also acted like any other
animal substance. I breathed on some leaves for above a minute, and
repeated the act two or three times, with my mouth close to [[page 24]]
them, but this produced no effect. I may here add, as showing that the
leaves are not acted on by the odour of nitrogenous substances, that
pieces of raw meat stuck on needles were fixed as close as possible,
without actual contact, to several leaves, but produced no effect
whatever. On the other hand, as we shall hereafter see, the vapours of
certain volatile substances and fluids, such as of carbonate of
ammonia, chloroform, certain essential oils, &c., cause inflection. M.
Ziegler makes still more extraordinary statements with respect to the
power of animal substances, which have been left close to, but not in
contact with, sulphate of quinine. The action of salts of quinine will
be described in a future chapter. Since the appearance of the paper
above referred to, M. Ziegler has published a book on the same subject,
entitled ‘Atonicit et Zoicit,’ 1874.) [page 24]


The Inflection of the Exterior Tentacles as directly caused by Objects
left in Contact with their Glands.

I made a vast number of trials by placing, by means of a fine needle
moistened with distilled water, and with the aid of a lens, particles
of various substances on the viscid secretion surrounding the glands of
the outer tentacles. I experimented on both the oval and long-headed
glands. When a particle is thus placed on a single gland, the movement
of the tentacle is particularly well seen in contrast with the
stationary condition of the surrounding tentacles. (See previous fig.
6.) In four cases small particles of raw meat caused the tentacles to
be greatly inflected in between 5 and 6 m. Another tentacle similarly
treated, and observed with special care, distinctly, though slightly,
changed its position in 10 s. (seconds); and this is the quickest
movement seen by me. In 2 m. 30 s. it had moved through an angle of
about 45o. The movement as seen through a lens resembled that of the
hand of a large clock. In 5 m. it had moved through 90o, and when I
looked again after 10 m., the particle had reached the centre of the
leaf; so that the whole movement was completed in less [page 25] than
17 m. 30 s. In the course of some hours this minute bit of meat, from
having been brought into contact with some of the glands of the central
disc, acted centrifugally on the outer tentacles, which all became
closely inflected. Fragments of flies were placed on the glands of four
of the outer tentacles, extended in the same plane with that of the
blade, and three of these fragments were carried in 35 m. through an
angle of 180o to the centre. The fragment on the fourth tentacle was
very minute, and it was not carried to the centre until 3 hrs. had
elapsed. In three other cases minute flies or portions of larger ones
were carried to the centre in 1 hr. 30 s. In these seven cases, the
fragments or small flies, which had been carried by a single tentacle
to the central glands, were well embraced by the other tentacles after
an interval of from 4 to 10 hrs.

I also placed in the manner just described six small balls of
writing-paper (rolled up by the aid of pincers, so that they were not
touched by my fingers) on the glands of six exterior tentacles on
distinct leaves; three of these were carried to the centre in about 1
hr., and the other three in rather more than 4 hrs.; but after 24 hrs.
only two of the six balls were well embraced by the other tentacles. It
is possible that the secretion may have dissolved a trace of glue or
animalised matter from the balls of paper. Four particles of
coal-cinder were then placed on the glands of four exterior tentacles;
one of these reached the centre in 3 hrs. 40 m.; the second in 9 hrs.;
the third within 24 hrs., but had moved only part of the way in 9 hrs.;
whilst the fourth moved only a very short distance in 24 hrs., and
never moved any farther. Of the above three bits of cinder which were
ultimately carried to the centre, one alone was well embraced by [page
26] many of the other tentacles. We here see clearly that such bodies
as particles of cinder or little balls of paper, after being carried by
the tentacles to the central glands, act very differently from
fragments of flies, in causing the movement of the surrounding
tentacles.

I made, without carefully recording the times of movement, many similar
trials with other substances, such as splinters of white and blue
glass, particles of cork, minute bits of gold-leaf, &c. and the
proportional number of cases varied much in which the tentacles reached
the centre, or moved only slightly, or not at all. One evening,
particles of glass and cork, rather larger than those usually employed,
were placed on about a dozen glands, and next morning, after 13 hrs.,
every single tentacle had carried its little load to the centre; but
the unusually large size of the particles will account for this result.
In another case 6/7 of the particles of cinder, glass, and thread,
placed on separate glands, were carried towards, or actually to, the
centre; in another case 7/9, in another 7/12, and in the last case only
7/26 were thus carried inwards, the small proportion being here due, at
least in part, to the leaves being rather old and inactive.
Occasionally a gland, with its light load, could be seen through a
strong lens to move an extremely short distance and then stop; this was
especially apt to occur when excessively minute particles, much less
than those of which the measurements will be immediately given, were
placed on glands; so that we here have nearly the limit of any action.

I was so much surprised at the smallness of the particles which caused
the tentacles to become greatly inflected that it seemed worth while
carefully to ascertain how minute a particle would plainly act. [page
27] Accordingly measured lengths of a narrow strip of blotting paper,
of fine cotton-thread, and of a woman’s hair, were carefully weighed
for me by Mr. Trenham Reeks, in an excellent balance, in the laboratory
in Jermyn Street. Short bits of the paper, thread, and hair were then
cut off and measured by a micrometer, so that their weights could be
easily calculated. The bits were placed on the viscid secretion
surrounding the glands of the exterior tentacles, with the precautions
already stated, and I am certain that the gland itself was never
touched; nor indeed would a single touch have produced any effect. A
bit of the blotting-paper, weighing 1/465 of a grain, was placed so as
to rest on three glands together, and all three tentacles slowly curved
inwards; each gland, therefore, supposing the weight to be distributed
equally, could have been pressed on by only 1/1395 of a grain, or .0464
of a milligramme. Five nearly equal bits of cotton-thread were tried,
and all acted. The shortest of these was 1/50 of an inch in length, and
weighed 1/8197 of a grain. The tentacle in this case was considerably
inflected in 1 hr. 30 m., and the bit of thread was carried to the
centre of the leaf in 1 hr. 40 m. Again, two particles of the thinner
end of a woman’s hair, one of these being 18/1000 of an inch in length,
and weighing 1/35714 of a grain, the other 19/1000 of an inch in
length, and weighing of course a little more, were placed on two glands
on opposite sides of the same leaf, and these two tentacles were
inflected halfway towards the centre in 1 hr. 10 m.; all the many other
tentacles round the same leaf remaining motionless. The appearance of
this one leaf showed in an unequivocal manner that these minute
particles sufficed to cause the tentacles to bend. Altogether, ten such
particles of hair were placed on ten glands on several leaves, and
seven of them caused [page 28] the tentacles to move in a conspicuous
manner. The smallest particle which was tried, and which acted plainly,
was only 8/1000 of an inch (.203 millimetre) in length, and weighed the
1/78740 of a grain, or .000822 milligramme. In these several cases, not
only was the inflection of the tentacles conspicuous, but the purple
fluid within their cells became aggregated into little masses of
protoplasm, in the manner to be described in the next chapter; and the
aggregation was so plain that I could, by this clue alone, have readily
picked out under the microscope all the tentacles which had carried
their light loads towards the centre, from the hundreds of other
tentacles on the same leaves which had not thus acted.

My surprise was greatly excited, not only by the minuteness of the
particles which caused movement, but how they could possibly act on the
glands; for it must be remembered that they were laid with the greatest
care on the convex surface of the secretion. At first I thought—but, as
I now know, erroneously—that particles of such low specific gravity as
those of cork, thread, and paper, would never come into contact with
the surfaces of the glands. The particles cannot act simply by their
weight being added to that of the secretion, for small drops of water,
many times heavier than the particles, were repeatedly added, and never
produced any effect. Nor does the disturbance of the secretion produce
any effect, for long threads were drawn out by a needle, and affixed to
some adjoining object, and thus left for hours; but the tentacles
remained motionless.

I also carefully removed the secretion from four glands with a sharply
pointed piece of blotting-paper, so that they were exposed for a time
naked to the air, but this caused no movement; yet these glands were
[page 29] in an efficient state, for after 24 hrs. had elapsed, they
were tried with bits of meat, and all became quickly inflected. It then
occurred to me that particles floating on the secretion would cast
shadows on the glands, which might be sensitive to the interception of
the light. Although this seemed highly improbable, as minute and thin
splinters of colourless glass acted powerfully, nevertheless, after it
was dark, I put on, by the aid of a single tallow candle, as quickly as
possible, particles of cork and glass on the glands of a dozen
tentacles, as well as some of meat on other glands, and covered them up
so that not a ray of light could enter; but by the next morning, after
an interval of 13 hrs., all the particles were carried to the centres
of the leaves.

These negative results led me to try many more experiments, by placing
particles on the surface of the drops of secretion, observing, as
carefully as I could, whether they penetrated it and touched the
surface of the glands. The secretion, from its weight, generally forms
a thicker layer on the under than on the upper sides of the glands,
whatever may be the position of the tentacles. Minute bits of dry cork,
thread, blotting paper, and coal cinders were tried, such as those
previously employed; and I now observed that they absorbed much more of
the secretion, in the course of a few minutes, than I should have
thought possible; and as they had been laid on the upper surface of the
secretion, where it is thinnest, they were often drawn down, after a
time, into contact with at least some one point of the gland. With
respect to the minute splinters of glass and particles of hair, I
observed that the secretion slowly spread itself a little over their
surfaces, by which means they were likewise drawn downwards or
sideways, and thus one end, or some minute [page 30] prominence, often
came to touch, sooner or later, the gland.

In the foregoing and following cases, it is probable that the
vibrations, to which the furniture in every room is continually liable,
aids in bringing the particles into contact with the glands. But as it
was sometimes difficult, owing to the refraction of the secretion, to
feel sure whether the particles were in contact, I tried the following
experiment. Unusually minute particles of glass, hair, and cork, were
gently placed on the drops round several glands, and very few of the
tentacles moved. Those which were not affected were left for about half
an hour, and the particles were then disturbed or tilted up several
times with a fine needle under the microscope, the glands not being
touched. And now in the course of a few minutes almost all the hitherto
motionless tentacles began to move; and this, no doubt, was caused by
one end or some prominence of the particles having come into contact
with the surface of the glands. But as the particles were unusually
minute, the movement was small.

Lastly, some dark blue glass pounded into fine splinters was used, in
order that the points of the particles might be better distinguished
when immersed in the secretion; and thirteen such particles were placed
in contact with the depending and therefore thicker part of the drops
round so many glands. Five of the tentacles began moving after an
interval of a few minutes, and in these cases I clearly saw that the
particles touched the lower surface of the gland. A sixth tentacle
moved after 1 hr. 45 m., and the particle was now in contact with the
gland, which was not the case at first. So it was with the seventh
tentacle, but its movement did not begin until 3 hrs. 45 m. had [page
31] elapsed. The remaining six tentacles never moved as long as they
were observed; and the particles apparently never came into contact
with the surfaces of the glands.

From these experiments we learn that particles not containing soluble
matter, when placed on glands, often cause the tentacles to begin
bending in the course of from one to five minutes; and that in such
cases the particles have been from the first in contact with the
surfaces of the glands. When the tentacles do not begin moving for a
much longer time, namely, from half an hour to three or four hours, the
particles have been slowly brought into contact with the glands, either
by the secretion being absorbed by the particles or by its gradual
spreading over them, together with its consequent quicker evaporation.
When the tentacles do not move at all, the particles have never come
into contact with the glands, or in some cases the tentacles may not
have been in an active condition. In order to excite movement, it is
indispensable that the particles should actually rest on the glands;
for a touch once, twice, or even thrice repeated by any hard body is
not sufficient to excite movement.

Another experiment, showing that extremely minute particles act on the
glands when immersed in water, may here be given. A grain of sulphate
of quinine was added to an ounce of water, which was not afterwards
filtered; and on placing three leaves in ninety minims of this fluid, I
was much surprised to find that all three leaves were greatly inflected
in 15 m.; for I knew from previous trials that the solution does not
act so quickly as this. It immediately occurred to me that the
particles of the undissolved salt, which were so light as to float
about, might have come [page 32] into contact with the glands, and
caused this rapid movement. Accordingly I added to some distilled water
a pinch of a quite innocent substance, namely, precipitated carbonate
of lime, which consists of an impalpable powder; I shook the mixture,
and thus got a fluid like thin milk. Two leaves were immersed in it,
and in 6 m. almost every tentacle was much inflected. I placed one of
these leaves under the microscope, and saw innumerable atoms of lime
adhering to the external surface of the secretion. Some, however, had
penetrated it, and were lying on the surfaces of the glands; and no
doubt it was these particles which caused the tentacles to bend. When a
leaf is immersed in water, the secretion instantly swells much; and I
presume that it is ruptured here and there, so that little eddies of
water rush in. If so, we can understand how the atoms of chalk, which
rested on the surfaces of the glands, had penetrated the secretion.
Anyone who has rubbed precipitated chalk between his fingers will have
perceived how excessively fine the powder is. No doubt there must be a
limit, beyond which a particle would be too small to act on a gland;
but what this limit is, I know not. I have often seen fibres and dust,
which had fallen from the air, on the glands of plants kept in my room,
and these never induced any movement; but then such particles lay on
the surface of the secretion and never reached the gland itself.

Finally, it is an extraordinary fact that a little bit of soft thread,
1/50 of an inch in length and weighing 1/8197 of a grain, or of a human
hair, 8/1000 of an inch in length and weighing only 1/78740 of a grain
(.000822 milligramme), or particles of precipitated chalk, after
resting for a short time on a gland, should induce some change in its
cells, exciting them [page 33] to transmit a motor impulse throughout
the whole length of the pedicel, consisting of about twenty cells, to
near its base, causing this part to bend, and the tentacle to sweep
through an angle of above 180o. That the contents of the cells of the
glands, and afterwards those of the pedicels, are affected in a plainly
visible manner by the pressure of minute particles, we shall have
abundant evidence when we treat of the aggregation of protoplasm. But
the case is much more remarkable than as yet stated; for the particles
are supported by the viscid and dense secretion; nevertheless, even
smaller ones than those of which the measurements have been given, when
brought by an insensibly slow movement, through the means above
specified, into contact with the surface of a gland, act on it, and the
tentacle bends. The pressure exerted by the particle of hair, weighing
only 1/78740 of a grain and supported by a dense fluid, must have been
inconceivably slight. We may conjecture that it could hardly have
equalled the millionth of a grain; and we shall hereafter see that far
less than the millionth of a grain of phosphate of ammonia in solution,
when absorbed by a gland, acts on it and induces movement. A bit of
hair, 1/50 of an inch in length, and therefore much larger than those
used in the above experiments, was not perceived when placed on my
tongue; and it is extremely doubtful whether any nerve in the human
body, even if in an inflamed condition, would be in any way affected by
such a particle supported in a dense fluid, and slowly brought into
contact with the nerve. Yet the cells of the glands of Drosera are thus
excited to transmit a motor impulse to a distant point, inducing
movement. It appears to me that hardly any more remarkable fact than
this has been observed in the vegetable kingdom. [page 34]

The Inflection of the Exterior Tentacles, when their Glands are excited
by Repeated Touches.

We have already seen that, if the central glands are excited by being
gently brushed, they transmit a motor impulse to the exterior
tentacles, causing them to bend; and we have now to consider the
effects which follow from the glands of the exterior tentacles being
themselves touched. On several occasions, a large number of glands were
touched only once with a needle or fine brush, hard enough to bend the
whole flexible tentacle; and though this must have caused a
thousand-fold greater pressure than the weight of the above described
particles, not a tentacle moved. On another occasion forty-five glands
on eleven leaves were touched once, twice, or even thrice, with a
needle or stiff bristle. This was done as quickly as possible, but with
force sufficient to bend the tentacles; yet only six of them became
inflected,—three plainly, and three in a slight degree. In order to
ascertain whether these tentacles which were not affected were in an
efficient state, bits of meat were placed on ten of them, and they all
soon became greatly incurved. On the other hand, when a large number of
glands were struck four, five, or six times with the same force as
before, a needle or sharp splinter of glass being used, a much larger
proportion of tentacles became inflected; but the result was so
uncertain as to seem capricious. For instance, I struck in the above
manner three glands, which happened to be extremely sensitive, and all
three were inflected almost as quickly, as if bits of meat had been
placed on them. On another occasion I gave a single for- [page 35]
cible touch to a considerable number of glands, and not one moved; but
these same glands, after an interval of some hours, being touched four
or five times with a needle, several of the tentacles soon became
inflected.

The fact of a single touch or even of two or three touches not causing
inflection must be of some service to the plant; as during stormy
weather, the glands cannot fail to be occasionally touched by the tall
blades of grass, or by other plants growing near; and it would be a
great evil if the tentacles were thus brought into action, for the act
of re-expansion takes a considerable time, and until the tentacles are
re-expanded they cannot catch prey. On the other hand, extreme
sensitiveness to slight pressure is of the highest service to the
plant; for, as we have seen, if the delicate feet of a minute
struggling insect press ever so lightly on the surfaces of two or three
glands, the tentacles bearing these glands soon curl inwards and carry
the insect with them to the centre, causing, after a time, all the
circumferential tentacles to embrace it. Nevertheless, the movements of
the plant are not perfectly adapted to its requirements; for if a bit
of dry moss, peat, or other rubbish, is blown on to the disc, as often
happens, the tentacles clasp it in a useless manner. They soon,
however, discover their mistake and release such innutritious objects.

It is also a remarkable fact, that drops of water falling from a
height, whether under the form of natural or artificial rain, do not
cause the tentacles to move; yet the drops must strike the glands with
considerable force, more especially after the secretion has been all
washed away by heavy rain; and this often occurs, [page 36] though the
secretion is so viscid that it can be removed with difficulty merely by
waving the leaves in water. If the falling drops of water are small,
they adhere to the secretion, the weight of which must be increased in
a much greater degree, as before remarked, than by the addition of
minute particles of solid matter; yet the drops never cause the
tentacles to become inflected. It would obviously have been a great
evil to the plant (as in the case of occasional touches) if the
tentacles were excited to bend by every shower of rain; but this evil
has been avoided by the glands either having become through habit
insensible to the blows and prolonged pressure of drops of water, or to
their having been originally rendered sensitive solely to the contact
of solid bodies. We shall hereafter see that the filaments on the
leaves of Dionaea are likewise insensible to the impact of fluids,
though exquisitely sensitive to momentary touches from any solid body.

When the pedicel of a tentacle is cut off by a sharp pair of scissors
quite close beneath the gland, the tentacle generally becomes
inflected. I tried this experiment repeatedly, as I was much surprised
at the fact, for all other parts of the pedicels are insensible to any
stimulus. These headless tentacles after a time re-expand; but I shall
return to this subject. On the other hand, I occasionally succeeded in
crushing a gland between a pair of pincers, but this caused no
inflection. In this latter case the tentacles seem paralysed, as
likewise follows from the action of too strong solutions of certain
salts, and by too great heat, whilst weaker solutions of the same salts
and a more gentle heat cause movement. We shall also see in future
chapters that various other fluids, some [page 37] vapours, and oxygen
(after the plant has been for some time excluded from its action), all
induce inflection, and this likewise results from an induced galvanic
current.*

* My son Francis, guided by the observations of Dr. Burdon Sanderson on
Dionaea, finds that if two needles are inserted into the blade of a
leaf of Drosera, the tentacles do not move; but that if similar needles
in connection with the secondary coil of a Du Bois inductive apparatus
are inserted, the tentacles curve inwards in the course of a few
minutes. My son hopes soon to publish an account of his observations.
[page 38]




CHAPTER III.
AGGREGATION OF THE PROTOPLASM WITHIN THE CELLS OF THE TENTACLES.


Nature of the contents of the cells before aggregation—Various causes
which excite aggregation—The process commences within the glands and
travels down the tentacles— Description of the aggregated masses and of
their spontaneous movements—Currents of protoplasm along the walls of
the cells—Action of carbonate of ammonia—The granules in the protoplasm
which flows along the walls coalesce with the central masses—Minuteness
of the quantity of carbonate of ammonia causing aggregation—Action of
other salts of ammonia—Of other substances, organic fluids, &c.—Of
water—Of heat—Redissolution of the aggregated masses—Proximate causes
of the aggregation of the protoplasm—Summary and concluding
remarks—Supplementary observations on aggregation in the roots of
plants.


I will here interrupt my account of the movements of the leaves, and
describe the phenomenon of aggregation, to which subject I have already
alluded. If the tentacles of a young, yet fully matured leaf, that has
never been excited or become inflected, be examined, the cells forming
the pedicels are seen to be filled with homogeneous, purple fluid. The
walls are lined by a layer of colourless, circulating protoplasm; but
this can be seen with much greater distinctness after the process of
aggregation has been partly effected than before. The purple fluid
which exudes from a crushed tentacle is somewhat coherent, and does not
mingle with the surrounding water; it contains much flocculent or
granular matter. But this matter may have been generated by the cells
having been crushed; some degree of aggregation having been thus almost
instantly caused. [page 39]

If a tentacle is examined some hours after the gland has been excited
by repeated touches, or by an inorganic or organic particle placed on
it, or by the absorption of certain fluids, it presents a wholly
changed appearance. The cells, instead of being filled with homogeneous
purple fluid, now contain variously shaped masses of purple matter,
suspended in a colourless or almost colourless fluid. The change is so
conspicuous that it is visible through a weak lens, and even sometimes
by the naked eye; the tentacles now have a mottled appearance, so that
one thus affected can be picked out with ease from all the others. The
same result follows if the glands on the disc are irritated in any
manner, so that the exterior tentacles become inflected; for their
contents will then be found in an aggregated condition, although their
glands have not as yet touched any object. But aggregation may occur
independently of inflection, as we shall presently see. By whatever
cause the process may have been excited, it commences within the
glands, and then travels down the tentacles. It can be observed much
more distinctly in the upper cells of the pedicels than within the
glands, as these are somewhat opaque. Shortly after the tentacles have
re-expanded, the little masses of protoplasm are all redissolved, and
the purple fluid within the cells becomes as homogeneous and
transparent as it was at first. The process of redissolution travels
upwards from the bases of the tentacles to the glands, and therefore in
a reversed direction to that of aggregation. Tentacles in an aggregated
condition were shown to Prof. Huxley, Dr. Hooker, and Dr. Burdon
Sanderson, who observed the changes under the microscope, and were much
struck with the whole phenomenon. [page 40]

The little masses of aggregated matter are of the most diversified
shapes, often spherical or oval, sometimes much elongated, or quite
irregular with thread- or necklace-like or club-formed projections.
They consist of thick, apparently viscid matter, which in the exterior
tentacles is of a purplish, and in the short distal tentacles of a
greenish, colour. These little masses incessantly change their forms
and positions, being never at rest. A single mass will often separate
into two, which afterwards reunite. Their movements are rather slow,
and resemble those of Amoebae or of the white corpuscles of the blood.
We

FIG. 7. (Drosera rotundifolia.) Diagram of the same cell of a tentacle,
showing the various forms successively assumed by the aggregated masses
of protoplasm.

may, therefore, conclude that they consist of protoplasm. If their
shapes are sketched at intervals of a few minutes, they are invariably
seen to have undergone great changes of form; and the same cell has
been observed for several hours. Eight rude, though accurate sketches
of the same cell, made at intervals of between 2 m. or 3 m., are here
given (fig. 7), and illustrate some of the simpler and commonest
changes. The cell A, when first sketched, included two oval masses of
purple protoplasm touching each other. These became separate, as shown
at B, and then reunited, as at C. After the next interval a very common
appearance was presented— [page 41] D, namely, the formation of an
extremely minute sphere at one end of an elongated mass. This rapidly
increased in size, as shown in E, and was then re-absorbed, as at F, by
which time another sphere had been formed at the opposite end.

The cell above figured was from a tentacle of a dark red leaf, which
had caught a small moth, and was examined under water. As I at first
thought that the movements of the masses might be due to the absorption
of water, I placed a fly on a leaf, and when after 18 hrs. all the
tentacles were well inflected, these were examined without being
immersed in water. The cell

FIG. 8. (Drosera rotundifolia.) Diagram of the same cell of a tentacle,
showing the various forms successively assumed by the aggregated masses
of protoplasm.

here represented (fig. 8) was from this leaf, being sketched eight
times in the course of 15 m. These sketches exhibit some of the more
remarkable changes which the protoplasm undergoes. At first, there was
at the base of the cell 1, a little mass on a short footstalk, and a
larger mass near the upper end, and these seemed quite separate.
Nevertheless, they may have been connected by a fine and invisible
thread of protoplasm, for on two other occasions, whilst one mass was
rapidly increasing, and another in the same cell rapidly decreasing, I
was able by varying the light and using a high power, to detect a
connecting thread of extreme tenuity, which evidently served as [page
42] the channel of communication between the two. On the other hand,
such connecting threads are sometimes seen to break, and their
extremities then quickly become club-headed. The other sketches in fig.
8 show the forms successively assumed.

Shortly after the purple fluid within the cells has become aggregated,
the little masses float about in a colourless or almost colourless
fluid; and the layer of white granular protoplasm which flows along the
walls can now be seen much more distinctly. The stream flows at an
irregular rate, up one wall and down the opposite one, generally at a
slower rate across the narrow ends of the elongated cells, and so round
and round. But the current sometimes ceases. The movement is often in
waves, and their crests sometimes stretch almost across the whole width
of the cell, and then sink down again. Small spheres of protoplasm,
apparently quite free, are often driven by the current round the cells;
and filaments attached to the central masses are swayed to and fro, as
if struggling to escape. Altogether, one of these cells with the ever
changing central masses, and with the layer of protoplasm flowing round
the walls, presents a wonderful scene of vital activity.

[Many observations were made on the contents of the cells whilst
undergoing the process of aggregation, but I shall detail only a few
cases under different heads. A small portion of a leaf was cut off,
placed under a high power, and the glands very gently pressed under a
compressor. In 15 m. I distinctly saw extremely minute spheres of
protoplasm aggregating themselves in the purple fluid; these rapidly
increased in size, both within the cells of the glands and of the upper
ends of the pedicels. Particles of glass, cork, and cinders were also
placed on the glands of many tentacles; in 1 hr. several of them were
inflected, but after 1 hr. 35 m. there was no aggregation. Other
tentacles with these particles were examined after 8 hrs., and [page
43] now all their cells had undergone aggregation; so had the cells of
the exterior tentacles which had become inflected through the
irritation transmitted from the glands of the disc, on which the
transported particles rested. This was likewise the case with the short
tentacles round the margins of the disc, which had not as yet become
inflected. This latter fact shows that the process of aggregation is
independent of the inflection of the tentacles, of which indeed we have
other and abundant evidence. Again, the exterior tentacles on three
leaves were carefully examined, and found to contain only homogeneous
purple fluid; little bits of thread were then placed on the glands of
three of them, and after 22 hrs. the purple fluid in their cells almost
down to their bases was aggregated into innumerable, spherical,
elongated, or filamentous masses of protoplasm. The bits of thread had
been carried some time previously to the central disc, and this had
caused all the other tentacles to become somewhat inflected; and their
cells had likewise undergone aggregation, which however, it should be
observed, had not as yet extended down to their bases, but was confined
to the cells close beneath the glands.

Not only do repeated touches on the glands* and the contact of minute
particles cause aggregation, but if glands, without being themselves
injured, are cut off from the summits of the pedicels, this induces a
moderate amount of aggregation in the headless tentacles, after they
have become inflected. On the other hand, if glands are suddenly
crushed between pincers, as was tried in six cases, the tentacles seem
paralysed by so great a shock, for they neither become inflected nor
exhibit any signs of aggregation.

Carbonate of Ammonia.—Of all the causes inducing aggregation, that
which, as far as I have seen, acts the quickest, and is the most
powerful, is a solution of carbonate of ammonia. Whatever its strength
may be, the glands are always affected first, and soon become quite
opaque, so as to appear black. For instance, I placed a leaf in a few
drops of a strong solution, namely, of one part to 146 of water (or 3
grs. to 1 oz.), and observed it under a high power. All the glands
began to

* Judging from an account of M. Heckel’s observations, which I have
only just seen quoted in the ‘Gardeners’ Chronicle’ (Oct. 10, 1874), he
appears to have observed a similar phenomenon in the stamens of
Berberis, after they have been excited by a touch and have moved; for
he says, “the contents of each individual cell are collected together
in the centre of the cavity.” [page 44]


darken in 10 s. (seconds); and in 13 s. were conspicuously darker. In 1
m. extremely small spherical masses of protoplasm could be seen arising
in the cells of the pedicels close beneath the glands, as well as in
the cushions on which the long-headed marginal glands rest. In several
cases the process travelled down the pedicels for a length twice or
thrice as great as that of the glands, in about 10 m. It was
interesting to observe the process momentarily arrested at each
transverse partition between two cells, and then to see the transparent
contents of the cell next below almost flashing into a cloudy mass. In
the lower part of the pedicels, the action proceeded slower, so that it
took about 20 m. before the cells halfway down the long marginal and
submarginal tentacles became aggregated.

We may infer that the carbonate of ammonia is absorbed by the glands,
not only from its action being so rapid, but from its effect being
somewhat different from that of other salts. As the glands, when
excited, secrete an acid belonging to the acetic series, the carbonate
is probably at once converted into a salt of this series; and we shall
presently see that the acetate of ammonia causes aggregation almost or
quite as energetically as does the carbonate. If a few drops of a
solution of one part of the carbonate to 437 of water (or 1 gr. to 1
oz.) be added to the purple fluid which exudes from crushed tentacles,
or to paper stained by being rubbed with them, the fluid and the paper
are changed into a pale dirty green. Nevertheless, some purple colour
could still be detected after 1 hr. 30 m. within the glands of a leaf
left in a solution of twice the above strength (viz. 2 grs. to 1 oz.);
and after 24 hrs. the cells of the pedicels close beneath the glands
still contained spheres of protoplasm of a fine purple tint. These
facts show that the ammonia had not entered as a carbonate, for
otherwise the colour would have been discharged. I have, however,
sometimes observed, especially with the long-headed tentacles on the
margins of very pale leaves immersed in a solution, that the glands as
well as the upper cells of the pedicels were discoloured; and in these
cases I presume that the unchanged carbonate had been absorbed. The
appearance above described, of the aggregating process being arrested
for a short time at each transverse partition, impresses the mind with
the idea of matter passing downwards from cell to cell. But as the
cells one beneath the other undergo aggregation when inorganic and
insoluble particles are placed on the glands, the process must be, at
least in these cases, one of molecular change, transmitted from the
glands, [page 45] independently of the absorption of any matter. So it
may possibly be in the case of the carbonate of ammonia. As, however,
the aggregation caused by this salt travels down the tentacles at a
quicker rate than when insoluble particles are placed on the glands, it
is probable that ammonia in some form is absorbed not only by the
glands, but passes down the tentacles.

Having examined a leaf in water, and found the contents of the cells
homogeneous, I placed it in a few drops of a solution of one part of
the carbonate to 437 of water, and attended to the cells immediately
beneath the glands, but did not use a very high power. No aggregation
was visible in 3 m.; but after 15 m. small spheres of protoplasm were
formed, more especially beneath the long-headed marginal glands; the
process, however, in this case took place with unusual slowness. In 25
m. conspicuous spherical masses were present in the cells of the
pedicels for a length about equal to that of the glands; and in 3 hrs.
to that of a third or half of the whole tentacle.

If tentacles with cells containing only very pale pink fluid, and
apparently but little protoplasm, are placed in a few drops of a weak
solution of one part of the carbonate to 4375 of water (1 gr. to 10
oz.), and the highly transparent cells beneath the glands are carefully
observed under a high power, these may be seen first to become slightly
cloudy from the formation of numberless, only just perceptible,
granules, which rapidly grow larger either from coalescence or from
attracting more protoplasm from the surrounding fluid. On one occasion
I chose a singularly pale leaf, and gave it, whilst under the
microscope, a single drop of a stronger solution of one part to 437 of
water; in this case the contents of the cells did not become cloudy,
but after 10 m. minute irregular granules of protoplasm could be
detected, which soon increased into irregular masses and globules of a
greenish or very pale purple tint; but these never formed perfect
spheres, though incessantly changing their shapes and positions.

With moderately red leaves the first effect of a solution of the
carbonate generally is the formation of two or three, or of several,
extremely minute purple spheres which rapidly increase in size. To give
an idea of the rate at which such spheres increase in size, I may
mention that a rather pale purple leaf placed under a slip of glass was
given a drop of a solution of one part to 292 of water, and in 13 m. a
few minute spheres of protoplasm were formed; one of these, after 2
hrs. 30 m., was about two-thirds of the diameter of the cell. After 4
hrs. 25 m. [page 46] it nearly equalled the cell in diameter; and a
second sphere about half as large as the first, together with a few
other minute ones, were formed. After 6 hrs. the fluid in which these
spheres floated was almost colourless. After 8 hrs. 35 m. (always
reckoning from the time when the solution was first added) four new
minute spheres had appeared. Next morning, after 22 hrs., there were,
besides the two large spheres, seven smaller ones, floating in
absolutely colourless fluid, in which some flocculent greenish matter
was suspended.

At the commencement of the process of aggregation, more especially in
dark red leaves, the contents of the cells often present a different
appearance, as if the layer of protoplasm (primordial utricle) which
lines the cells had separated itself and shrunk from the walls; an
irregularly shaped purple bag being thus formed. Other fluids, besides
a solution of the carbonate, for instance an infusion of raw meat,
produce this same effect. But the appearance of the primordial utricle
shrinking from the walls is certainly false;* for before giving the
solution, I saw on several occasions that the walls were lined with
colourless flowing protoplasm, and after the bag-like masses were
formed, the protoplasm was still flowing along the walls in a
conspicuous manner, even more so than before. It appeared indeed as if
the stream of protoplasm was strengthened by the action of the
carbonate, but it was impossible to ascertain whether this was really
the case. The bag-like masses, when once formed, soon begin to glide
slowly round the cells, sometimes sending out projections which
separate into little spheres; other spheres appear in the fluid
surrounding the bags, and these travel much more quickly. That the
small spheres are separate is often shown by sometimes one and then
another travelling in advance, and sometimes they revolve round each
other. I have occasionally seen spheres of this kind proceeding up and
down the same side of a cell, instead of round it. The bag-like masses
after a time generally divide into two rounded or oval masses, and
these undergo the changes shown in figs. 7 and 8. At other times
spheres appear within the bags; and these coalesce and separate in an
endless cycle of change.

After leaves have been left for several hours in a solution of the
carbonate, and complete aggregation has been effected, the

* With other plants I have often seen what appears to be a true
shrinking of the primordial utricle from the walls of the cells, caused
by a solution of carbonate of ammonia, as likewise follows from
mechanical injuries. [page 47]


stream of protoplasm on the walls of the cells ceases to be visible; I
observed this fact repeatedly, but will give only one instance. A pale
purple leaf was placed in a few drops of a solution of one part to 292
of water, and in 2 hrs. some fine purple spheres were formed in the
upper cells of the pedicels, the stream of protoplasm round their walls
being still quite distinct; but after an additional 4 hrs., during
which time many more spheres were formed, the stream was no longer
distinguishable on the most careful examination; and this no doubt was
due to the contained granules having become united with the spheres, so
that nothing was left by which the movement of the limpid protoplasm
could be perceived. But minute free spheres still travelled up and down
the cells, showing that there was still a current. So it was next
morning, after 22 hrs., by which time some new minute spheres had been
formed; these oscillated from side to side and changed their positions,
proving that the current had not ceased, though no stream of protoplasm
was visible. On another occasion, however, a stream was seen flowing
round the cell-walls of a vigorous, dark-coloured leaf, after it had
been left for 24 hrs. in a rather stronger solution, namely, of one
part of the carbonate to 218 of water. This leaf, therefore, was not
much or at all injured by an immersion for this length of time in the
above solution of two grains to the ounce; and on being afterwards left
for 24 hrs. in water, the aggregated masses in many of the cells were
re-dissolved, in the same manner as occurs with leaves in a state of
nature when they re-expand after having caught insects.

In a leaf which had been left for 22 hrs. in a solution of one part of
the carbonate to 292 of water, some spheres of protoplasm (formed by
the self-division of a bag-like mass) were gently pressed beneath a
covering glass, and then examined under a high power. They were now
distinctly divided by well-defined radiating fissures, or were broken
up into separate fragments with sharp edges; and they were solid to the
centre. In the larger broken spheres the central part was more opaque,
darker-coloured, and less brittle than the exterior; the latter alone
being in some cases penetrated by the fissures. In many of the spheres
the line of separation between the outer and inner parts was tolerably
well defined. The outer parts were of exactly the same very pale purple
tint, as that of the last formed smaller spheres; and these latter did
not include any darker central core.

From these several facts we may conclude that when vigorous
dark-coloured leaves are subjected to the action of carbonate of [page
48] ammonia, the fluid within the cells of the tentacles often
aggregates exteriorly into coherent viscid matter, forming a kind of
bag. Small spheres sometimes appear within this bag, and the whole
generally soon divides into two or more spheres, which repeatedly
coalesce and redivide. After a longer or shorter time the granules in
the colourless layer of protoplasm, which flows round the walls, are
drawn to and unite with the larger spheres, or form small independent
spheres; these latter being of a much paler colour, and more brittle
than the first aggregated masses. After the granules of protoplasm have
been thus attracted, the layer of flowing protoplasm can no longer be
distinguished, though a current of limpid fluid still flows round the
walls.

If a leaf is immersed in a very strong, almost concentrated, solution
of carbonate of ammonia, the glands are instantly blackened, and they
secrete copiously; but no movement of the tentacles ensues. Two leaves
thus treated became after 1 hr. flaccid, and seemed killed; all the
cells in their tentacles contained spheres of protoplasm, but these
were small and discoloured. Two other leaves were placed in a solution
not quite so strong, and there was well-marked aggregation in 30 m.
After 24 hrs. the spherical or more commonly oblong masses of
protoplasm became opaque and granular, instead of being as usual
translucent; and in the lower cells there were only innumerable minute
spherical granules. It was evident that the strength of the solution
had interfered with the completion of the process, as we shall see
likewise follows from too great heat.

All the foregoing observations relate to the exterior tentacles, which
are of a purple colour; but the green pedicels of the short central
tentacles are acted on by the carbonate, and by an infusion of raw
meat, in exactly the same manner, with the sole difference that the
aggregated masses are of a greenish colour; so that the process is in
no way dependent on the colour of the fluid within the cells.

Finally, the most remarkable fact with respect to this salt is the
extraordinary small amount which suffices to cause aggregation. Full
details will be given in the seventh chapter, and here it will be
enough to say that with a sensitive leaf the absorption by a gland of
1/134400 of a grain (.000482 mgr.) is enough to cause in the course of
one hour well-marked aggregation in the cells immediately beneath the
gland.

The Effects of certain other Salts and Fluids.—Two leaves were placed
in a solution of one part of acetate of ammonia to about [page 49] 146
of water, and were acted on quite as energetically, but perhaps not
quite so quickly, as by the carbonate. After 10 m. the glands were
black, and in the cells beneath them there were traces of aggregation,
which after 15 m. was well marked, extending down the tentacles for a
length equal to that of the glands. After 2 hrs. the contents of almost
all the cells in all the tentacles were broken up into masses of
protoplasm. A leaf was immersed in a solution of one part of oxalate of
ammonia to 146 of water; and after 24 m. some, but not a conspicuous,
change could be seen within the cells beneath the glands. After 47 m.
plenty of spherical masses of protoplasm were formed, and these
extended down the tentacles for about the length of the glands. This
salt, therefore, does not act so quickly as the carbonate. With respect
to the citrate of ammonia, a leaf was placed in a little solution of
the above strength, and there was not even a trace of aggregation in
the cells beneath the glands, until 56 m. had elapsed; but it was well
marked after 2 hrs. 20 m. On another occasion a leaf was placed in a
stronger solution, of one part of the citrate to 109 of water (4 grs.
to 1 oz.), and at the same time another leaf in a solution of the
carbonate of the same strength. The glands of the latter were blackened
in less than 2 m., and after 1 hr. 45 m. the aggregated masses, which
were spherical and very dark-coloured, extended down all the tentacles,
for between half and two-thirds of their lengths; whereas in the leaf
immersed in the citrate the glands, after 30 m., were of a dark red,
and the aggregated masses in the cells beneath them pink and elongated.
After 1 hr. 45 m. these masses extended down for only about one-fifth
or one-fourth of the length of the tentacles.

Two leaves were placed, each in ten minims of a solution of one part of
nitrate of ammonia to 5250 of water (1 gr. to 12 oz.), so that each
leaf received 1/576 of a grain (.1124 mgr.). This quantity caused all
the tentacles to be inflected, but after 24 hrs. there was only a trace
of aggregation. One of these same leaves was then placed in a weak
solution of the carbonate, and after 1 hr. 45 m. the tentacles for half
their lengths showed an astonishing degree of aggregation. Two other
leaves were then placed in a much stronger solution of one part of the
nitrate to 146 of water (3 grs. to 1 oz.); in one of these there was no
marked change after 3 hrs.; but in the other there was a trace of
aggregation after 52 m., and this was plainly marked after 1 hr. 22 m.,
but even after 2 hrs. 12 m. there was certainly not more aggregation
than would have fol- [page 50] lowed from an immersion of from 5 m. to
10 m. in an equally strong solution of the carbonate.

Lastly, a leaf was placed in thirty minims of a solution of one part of
phosphate of ammonia to 43,750 of water (1 gr. to 100 oz.), so that it
received 1/1600 of a grain (.04079 mgr.); this soon caused the
tentacles to be strongly inflected; and after 24 hrs. the contents of
the cells were aggregated into oval and irregularly globular masses,
with a conspicuous current of protoplasm flowing round the walls. But
after so long an interval aggregation would have ensued, whatever had
caused inflection.

Only a few other salts, besides those of ammonia, were tried in
relation to the process of aggregation. A leaf was placed in a solution
of one part of chloride of sodium to 218 of water, and after 1 hr. the
contents of the cells were aggregated into small, irregularly globular,
brownish masses; these after 2 hrs. were almost disintegrated and
pulpy. It was evident that the protoplasm had been injuriously
affected; and soon afterwards some of the cells appeared quite empty.
These effects differ altogether from those produced by the several
salts of ammonia, as well as by various organic fluids, and by
inorganic particles placed on the glands. A solution of the same
strength of carbonate of soda and carbonate of potash acted in nearly
the same manner as the chloride; and here again, after 2 hrs. 30 m.,
the outer cells of some of the glands had emptied themselves of their
brown pulpy contents. We shall see in the eighth chapter that solutions
of several salts of soda of half the above strength cause inflection,
but do not injure the leaves. Weak solutions of sulphate of quinine, of
nicotine, camphor, poison of the cobra, &c., soon induce well-marked
aggregation; whereas certain other substances (for instance, a solution
of curare) have no such tendency.

Many acids, though much diluted, are poisonous; and though, as will be
shown in the eighth chapter, they cause the tentacles to bend, they do
not excite true aggregation. Thus leaves were placed in a solution of
one part of benzoic acid to 437 of water; and in 15 m. the purple fluid
within the cells had shrunk a little from the walls, yet when carefully
examined after 1 hr. 20 m., there was no true aggregation; and after 24
hrs. the leaf was evidently dead. Other leaves in iodic acid, diluted
to the same degree, showed after 2 hrs. 15 m. the same shrunken
appearance of the purple fluid within the cells; and these, after 6
hrs. 15 m., were seen under a high power to be filled with excessively
minute spheres of dull reddish protoplasm, [page 51] which by the next
morning, after 24 hrs., had almost disappeared, the leaf being
evidently dead. Nor was there any true aggregation in leaves immersed
in propionic acid of the same strength; but in this case the protoplasm
was collected in irregular masses towards the bases of the lower cells
of the tentacles.

A filtered infusion of raw meat induces strong aggregation, but not
very quickly. In one leaf thus immersed there was a little aggregation
after 1 hr. 20 m., and in another after 1 hr. 50 m. With other leaves a
considerably longer time was required: for instance, one immersed for 5
hrs. showed no aggregation, but was plainly acted on in 5 m.; when
placed in a few drops of a solution of one part of carbonate of ammonia
to 146 of water. Some leaves were left in the infusion for 24 hrs., and
these became aggregated to a wonderful degree, so that the inflected
tentacles presented to the naked eye a plainly mottled appearance. The
little masses of purple protoplasm were generally oval or beaded, and
not nearly so often spherical as in the case of leaves subjected to
carbonate of ammonia. They underwent incessant changes of form; and the
current of colourless protoplasm round the walls was conspicuously
plain after an immersion of 25 hrs. Raw meat is too powerful a
stimulant, and even small bits generally injure, and sometimes kill,
the leaves to which they are given: the aggregated masses of protoplasm
become dingy or almost colourless, and present an unusual granular
appearance, as is likewise the case with leaves which have been
immersed in a very strong solution of carbonate of ammonia. A leaf
placed in milk had the contents of its cells somewhat aggregated in 1
hr. Two other leaves, one immersed in human saliva for 2 hrs. 30 m.,
and another in unboiled white of egg for 1 hr. 30 m., were not action
on in this manner; though they undoubtedly would have been so, had more
time been allowed. These same two leaves, on being afterwards placed in
a solution of carbonate of ammonia (3 grs. to 1 oz.), had their cells
aggregated, the one in 10 m. and the other in 5 m.

Several leaves were left for 4 hrs. 30 m. in a solution of one part of
white sugar to 146 of water, and no aggregation ensued; on being placed
in a solution of this same strength of carbonate of ammonia, they were
acted on in 5 m.; as was likewise a leaf which had been left for 1 hr.
45 m. in a moderately thick solution of gum arabic. Several other
leaves were immersed for some hours in denser solutions of sugar, gum,
and starch, and they had the contents of their cells greatly
aggregated. This [page 52] effect may be attributed to exosmose; for
the leaves in the syrup became quite flaccid, and those in the gum and
starch somewhat flaccid, with their tentacles twisted about in the most
irregular manner, the longer ones like corkscrews. We shall hereafter
see that solutions of these substances, when placed on the discs of
leaves, do not incite inflection. Particles of soft sugar were added to
the secretion round several glands and were soon dissolved, causing a
great increase of the secretion, no doubt by exosmose; and after 24
hrs. the cells showed a certain amount of aggregation, though the
tentacles were not inflected. Glycerine causes in a few minutes
well-pronounced aggregation, commencing as usual within the glands and
then travelling down the tentacles; and this I presume may be
attributed to the strong attraction of this substance for water.
Immersion for several hours in water causes some degree of aggregation.
Twenty leaves were first carefully examined, and re-examined after
having been left immersed in distilled water for various periods, with
the following results. It is rare to find even a trace of aggregation
until 4 or 5 and generally not until several more hours have elapsed.
When however a leaf becomes quickly inflected in water, as sometimes
happens, especially during very warm weather, aggregation may occur in
little over 1 hr. In all cases leaves left in water for more than 24
hrs. have their glands blackened, which shows that their contents are
aggregated; and in the specimens which were carefully examined, there
was fairly well-marked aggregation in the upper cells of the pedicels.
These trials were made with cut off-leaves, and it occurred to me that
this circumstance might influence the result, as the footstalks would
not perhaps absorb water quickly enough to supply the glands as they
continued to secrete. But this view was proved erroneous, for a plant
with uninjured roots, bearing four leaves, was submerged in distilled
water for 47 hrs., and the glands were blackened, though the tentacles
were very little inflected. In one of these leaves there was only a
slight degree of aggregation in the tentacles; in the second rather
more, the purple contents of the cells being a little separated from
the walls; in the third and fourth, which were pale leaves, the
aggregation in the upper parts of the pedicels was well marked. In
these leaves the little masses of protoplasm, many of which were oval,
slowly changed their forms and positions; so that a submergence for 47
hrs. had not killed the protoplasm. In a previous trial with a
submerged plant, the tentacles were not in the least inflected. [page
53]

Heat induces aggregation. A leaf, with the cells of the tentacles
containing only homogeneous fluid, was waved about for 1 m. in water at
130° Fahr. (54°.4 Cent.) and was then examined under the microscope as
quickly as possible, that is in 2 m. or 3 m.; and by this time the
contents of the cells had undergone some degree of aggregation. A
second leaf was waved for 2 m. in water at 125° (51°.6 Cent.) and
quickly examined as before; the tentacles were well inflected; the
purple fluid in all the cells had shrunk a little from the walls, and
contained many oval and elongated masses of protoplasm, with a few
minute spheres. A third leaf was left in water at 125°, until it
cooled, and when examined after 1 hr. 45 m., the inflected tentacles
showed some aggregation, which became after 3 hrs. more strongly
marked, but did not subsequently increase. Lastly, a leaf was waved for
1 m. in water at 120° (48°.8 Cent.) and then left for 1 hr. 26 m. in
cold water; the tentacles were but little inflected, and there was only
here and there a trace of aggregation. In all these and other trials
with warm water the protoplasm showed much less tendency to aggregate
into spherical masses than when excited by carbonate of ammonia.

Redissolution of the Aggregated Masses of Protoplasm.—As soon as
tentacles which have clasped an insect or any inorganic object, or have
been in any way excited, have fully re-expanded, the aggregated masses
of protoplasm are redissolved and disappear; the cells being now
refilled with homogeneous purple fluid as they were before the
tentacles were inflected. The process of redissolution in all cases
commences at the bases of the tentacles, and proceeds up them towards
the glands. In old leaves, however, especially in those which have been
several times in action, the protoplasm in the uppermost cells of the
pedicels remains in a permanently more or less aggregated condition. In
order to observe the process of redissolution, the following
observations were made: a leaf was left for 24 hrs. in a little
solution of one part of carbonate of ammonia to 218 of water, and the
protoplasm was as usual aggregated into numberless purple spheres,
which were incessantly changing their forms. The leaf was then washed
and placed in distilled water, and after 3 hrs. 15 m. some few of the
spheres began to show by their less clearly defined edges signs of
redissolution. After 9 hrs. many of them had become elongated, and the
surrounding fluid in the cells was slightly more coloured, showing
plainly that redissolution had commenced. After 24 hrs., though many
cells still contained spheres, here and there one [page 54] could be
seen filled with purple fluid, without a vestige of aggregated
protoplasm; the whole having been redissolved. A leaf with aggregated
masses, caused by its having been waved for 2 m. in water at the
temperature of 125° Fahr., was left in cold water, and after 11 hrs.
the protoplasm showed traces of incipient redissolution. When again
examined three days after its immersion in the warm water, there was a
conspicuous difference, though the protoplasm was still somewhat
aggregated. Another leaf, with the contents of all the cells strongly
aggregated from the action of a weak solution of phosphate of ammonia,
was left for between three and four days in a mixture (known to be
innocuous) of one drachm of alcohol to eight drachms of water, and when
re-examined every trace of aggregation had disappeared, the cells being
now filled with homogeneous fluid.

We have seen that leaves immersed for some hours in dense solutions of
sugar, gum, and starch, have the contents of their cells greatly
aggregated, and are rendered more or less flaccid, with the tentacles
irregularly contorted. These leaves, after being left for four days in
distilled water, became less flaccid, with their tentacles partially
re-expanded, and the aggregated masses of protoplasm were partially
redissolved. A leaf with its tentacles closely clasped over a fly, and
with the contents of the cells strongly aggregated, was placed in a
little sherry wine; after 2 hrs. several of the tentacles had
re-expanded, and the others could by a mere touch be pushed back into
their properly expanded positions, and now all traces of aggregation
had disappeared, the cells being filled with perfectly homogeneous pink
fluid. The redissolution in these cases may, I presume, be attributed
to endosmose.]

_On the Proximate Causes of the Process of Aggregation._


As most of the stimulants which cause the inflection of the tentacles
likewise induce aggregation in the contents of their cells, this latter
process might be thought to be the direct result of inflection; but
this is not the case. If leaves are placed in rather strong solutions
of carbonate of ammonia, for instance of three or four, and even
sometimes of only two grains to the ounce of water (i.e. one part to
109, or 146, or [page 55] 218, of water), the tentacles are paralysed,
and do not become inflected, yet they soon exhibit strongly marked
aggregation. Moreover, the short central tentacles of a leaf which has
been immersed in a weak solution of any salt of ammonia, or in any
nitrogenous organic fluid, do not become in the least inflected;
nevertheless they exhibit all the phenomena of aggregation. On the
other hand, several acids cause strongly pronounced inflection, but no
aggregation.

It is an important fact that when an organic or inorganic object is
placed on the glands of the disc, and the exterior tentacles are thus
caused to bend inwards, not only is the secretion from the glands of
the latter increased in quantity and rendered acid, but the contents of
the cells of their pedicels become aggregated. The process always
commences in the glands, although these have not as yet touched any
object. Some force or influence must, therefore, be transmitted from
the central glands to the exterior tentacles, first to near their bases
causing this part to bend, and next to the glands causing them to
secrete more copiously. After a short time the glands, thus indirectly
excited, transmit or reflect some influence down their own pedicels,
inducing aggregation in cell beneath cell to their bases.

It seems at first sight a probable view that aggregation is due to the
glands being excited to secrete more copiously, so that sufficient
fluid is not left in their cells, and in the cells of the pedicels, to
hold the protoplasm in solution. In favour of this view is the fact
that aggregation follows the inflection of the tentacles, and during
the movement the glands generally, or, as I believe, always, secrete
more copiously than they did before. Again, during the re-expansion
[page 56] of the tentacles, the glands secrete less freely, or quite
cease to secrete, and the aggregated masses of protoplasm are then
redissolved. Moreover, when leaves are immersed in dense vegetable
solutions, or in glycerine, the fluid within the gland-cells passes
outwards, and there is aggregation; and when the leaves are afterwards
immersed in water, or in an innocuous fluid of less specific gravity
than water, the protoplasm is redissolved, and this, no doubt, is due
to endosmose.

Opposed to this view, that aggregation is caused by the outward passage
of fluid from the cells, are the following facts. There seems no close
relation between the degree of increased secretion and that of
aggregation. Thus a particle of sugar added to the secretion round a
gland causes a much greater increase of secretion, and much less
aggregation, than does a particle of carbonate of ammonia given in the
same manner. It does not appear probable that pure water would cause
much exosmose, and yet aggregation often follows from an immersion in
water of between 16 hrs. and 24 hrs., and always after from 24 hrs. to
48 hrs. Still less probable is it that water at a temperature of from
125° to 130° Fahr. (51°.6 to 54°.4 Cent.) should cause fluid to pass,
not only from the glands, but from all the cells of the tentacles down
to their bases, so quickly that aggregation is induced within 2 m. or 3
m. Another strong argument against this view is, that, after complete
aggregation, the spheres and oval masses of protoplasm float about in
an abundant supply of thin colourless fluid; so that at least the
latter stages of the process cannot be due to the want of fluid to hold
the protoplasm in solution. There is still stronger evidence that
aggregation is independent of secretion; for the papillae, described in
the first chapter, with which the [page 57] leaves are studded are not
glandular, and do not secrete, yet they rapidly absorb carbonate of
ammonia or an infusion of raw meat, and their contents then quickly
undergo aggregation, which afterwards spreads into the cells of the
surrounding tissues. We shall hereafter see that the purple fluid
within the sensitive filaments of Dionaea, which do not secrete,
likewise undergoes aggregation from the action of a weak solution of
carbonate of ammonia.

The process of aggregation is a vital one; by which I mean that the
contents of the cells must be alive and uninjured to be thus affected,
and they must be in an oxygenated condition for the transmission of the
process at the proper rate. Some tentacles in a drop of water were
strongly pressed beneath a slip of glass; many of the cells were
ruptured, and pulpy matter of a purple colour, with granules of all
sizes and shapes, exuded, but hardly any of the cells were completely
emptied. I then added a minute drop of a solution of one part of
carbonate of ammonia to 109 of water, and after 1 hr. examined the
specimens. Here and there a few cells, both in the glands and in the
pedicels, had escaped being ruptured, and their contents were well
aggregated into spheres which were constantly changing their forms and
positions, and a current could still be seen flowing along the walls;
so that the protoplasm was alive. On the other hand, the exuded matter,
which was now almost colourless instead of being purple, did not
exhibit a trace of aggregation. Nor was there a trace in the many cells
which were ruptured, but which had not been completely emptied of their
contents. Though I looked carefully, no signs of a current could be
seen within these ruptured cells. They had evidently been killed by the
pressure; and the matter which they [page 58] still contained did not
undergo aggregation any more than that which had exuded. In these
specimens, as I may add, the individuality of the life of each cell was
well illustrated.

A full account will be given in the next chapter of the effects of heat
on the leaves, and I need here only state that leaves immersed for a
short time in water at a temperature of 120° Fahr. (48°.8 Cent.),
which, as we have seen, does not immediately induce aggregation, were
then placed in a few drops of a strong solution of one part of
carbonate of ammonia to 109 of water, and became finely aggregated. On
the other hand, leaves, after an immersion in water at 150° (65°.5
Cent.), on being placed in the same strong solution, did not undergo
aggregation, the cells becoming filled with brownish, pulpy, or muddy
matter. With leaves subjected to temperatures between these two
extremes of 120° and 150° Fahr. (48°.8 and 65°.5 Cent.), there were
gradations in the completeness of the process; the former temperature
not preventing aggregation from the subsequent action of carbonate of
ammonia, the latter quite stopping it. Thus, leaves immersed in water,
heated to 130° (54°.4 Cent.), and then in the solution, formed
perfectly defined spheres, but these were decidedly smaller than in
ordinary cases. With other leaves heated to 140° (60° Cent.), the
spheres were extremely small, yet well defined, but many of the cells
contained, in addition, some brownish pulpy matter. In two cases of
leaves heated to 145° (62°.7 Cent.), a few tentacles could be found
with some of their cells containing a few minute spheres; whilst the
other cells and other whole tentacles included only the brownish,
disintegrated or pulpy matter.

The fluid within the cells of the tentacles must be in an oxygenated
condition, in order that the force or [page 59] influence which induces
aggregation should be transmitted at the proper rate from cell to cell.
A plant, with its roots in water, was left for 45 m. in a vessel
containing 122 oz. of carbonic acid. A leaf from this plant, and, for
comparison, one from a fresh plant, were both immersed for 1 hr. in a
rather strong solution of carbonate of ammonia. They were then
compared, and certainly there was much less aggregation in the leaf
which had been subjected to the carbonic acid than in the other.
Another plant was exposed in the same vessel for 2 hrs. to carbonic
acid, and one of its leaves was then placed in a solution of one part
of the carbonate to 437 of water; the glands were instantly blackened,
showing that they had absorbed, and that their contents were
aggregated; but in the cells close beneath the glands there was no
aggregation even after an interval of 3 hrs. After 4 hrs. 15 m. a few
minute spheres of protoplasm were formed in these cells, but even after
5 hrs. 30 m. the aggregation did not extend down the pedicels for a
length equal to that of the glands. After numberless trials with fresh
leaves immersed in a solution of this strength, I have never seen the
aggregating action transmitted at nearly so slow a rate. Another plant
was left for 2 hrs. in carbonic acid, but was then exposed for 20 m. to
the open air, during which time the leaves, being of a red colour,
would have absorbed some oxygen. One of them, as well as a fresh leaf
for comparison, were now immersed in the same solution as before. The
former were looked at repeatedly, and after an interval of 65 m. a few
spheres of protoplasm were first observed in the cells close beneath
the glands, but only in two or three of the longer tentacles. After 3
hrs. the aggregation had travelled down the pedicels of a few of the
tentacles [page 60] for a length equal to that of the glands. On the
other hand, in the fresh leaf similarly treated, aggregation was plain
in many of the tentacles after 15 m.; after 65 m. it had extended down
the pedicels for four, five, or more times the lengths of the glands;
and after 3 hrs. the cells of all the tentacles were affected for
one-third or one-half of their entire lengths. Hence there can be no
doubt that the exposure of leaves to carbonic acid either stops for a
time the process of aggregation, or checks the transmission of the
proper influence when the glands are subsequently excited by carbonate
of ammonia; and this substance acts more promptly and energetically
than any other. It is known that the protoplasm of plants exhibits its
spontaneous movements only as long as it is in an oxygenated condition;
and so it is with the white corpuscles of the blood, only as long as
they receive oxygen from the red corpuscles;* but the cases above given
are somewhat different, as they relate to the delay in the generation
or aggregation of the masses of protoplasm by the exclusion of oxygen.

A Summary and Concluding Remarks.—The process of aggregation is
independent of the inflection of the tentacles and of increased
secretion from the glands. It commences within the glands, whether
these have been directly excited, or indirectly by a stimulus received
from other glands. In both cases the process is transmitted from cell
to cell down the whole length of the tentacles, being arrested for a
short time at each transverse partition. With pale-coloured leaves the
first change which is perceptible, but only

* With respect to plants, Sachs, ‘Traité de Bot.’ 3rd edit., 1874, p.
864. On blood corpuscles, see ‘Quarterly Journal of Microscopical
Science,’ April 1874, p. 185.’ [page 61]


under a high power, is the appearance of the finest granules in the
fluid within the cells, making it slightly cloudy. These granules soon
aggregate into small globular masses. I have seen a cloud of this kind
appear in 10 s. after a drop of a solution of carbonate of ammonia had
been given to a gland. With dark red leaves the first visible change
often is the conversion of the outer layer of the fluid within the
cells into bag-like masses. The aggregated masses, however they may
have been developed, incessantly change their forms and positions. They
are not filled with fluid, but are solid to their centres. Ultimately
the colourless granules in the protoplasm which flows round the walls
coalesce with the central spheres or masses; but there is still a
current of limpid fluid flowing within the cells. As soon as the
tentacles fully re-expand, the aggregated masses are redissolved, and
the cells become filled with homogeneous purple fluid, as they were at
first. The process of redissolution commences at the bases of the
tentacles, thence proceeding upwards to the glands; and, therefore, in
a reversed direction to that of aggregation.

Aggregation is excited by the most diversified causes,—by the glands
being several times touched,—by the pressure of particles of any kind,
and as these are supported by the dense secretion, they can hardly
press on the glands with the weight of a millionth of a grain,*—by the
tentacles being cut off close beneath

* According to Hofmeister (as quoted by Sachs, ‘Traité de Bot.’ 1874,
p. 958), very slight pressure on the cell-membrane arrests immediately
the movements of the protoplasm, and even determines its separation
from the walls. But the process of aggregation is a different
phenomenon, as it relates to the contents of the cells, and only
secondarily to the layer of protoplasm which flows along the walls;
though no doubt the effects of pressure or of a touch on the outside
must be transmitted through this layer. [page 62]


the glands,—by the glands absorbing various fluids or matter dissolved
out of certain bodies,—by exosmose,—and by a certain degree of heat. On
the other hand, a temperature of about 150° Fahr. (65°.5 Cent.) does
not excite aggregation; nor does the sudden crushing of a gland. If a
cell is ruptured, neither the exuded matter nor that which still
remains within the cell undergoes aggregation when carbonate of ammonia
is added. A very strong solution of this salt and rather large bits of
raw meat prevent the aggregated masses being well developed. From these
facts we may conclude that the protoplasmic fluid within a cell does
not become aggregated unless it be in a living state, and only
imperfectly if the cell has been injured. We have also seen that the
fluid must be in an oxygenated state, in order that the process of
aggregation should travel from cell to cell at the proper rate.

Various nitrogenous organic fluids and salts of ammonia induce
aggregation, but in different degrees and at very different rates.
Carbonate of ammonia is the most powerful of all known substances; the
absorption of 1/134400 of a grain (.000482 mg.) by a gland suffices to
cause all the cells of the same tentacle to become aggregated. The
first effect of the carbonate and of certain other salts of ammonia, as
well as of some other fluids, is the darkening or blackening of the
glands. This follows even from long immersion in cold distilled water.
It apparently depends in chief part on the strong aggregation of their
cell-contents, which thus become opaque, and do not reflect light. Some
other fluids render the glands of a brighter red; whilst certain acids,
though much diluted, the poison of the cobra-snake, &c., make the
glands perfectly white and opaque; and this seems to depend on the
coagulation of their contents without [page 63] any aggregation.
Nevertheless, before being thus affected, they are able, at least in
some cases, to excite aggregation in their own tentacles.

That the central glands, if irritated, send centrifugally some
influence to the exterior glands, causing them to send back a
centripetal influence inducing aggregation, is perhaps the most
interesting fact given in this chapter. But the whole process of
aggregation is in itself a striking phenomenon. Whenever the peripheral
extremity of a nerve is touched or pressed, and a sensation is felt, it
is believed that an invisible molecular change is sent from one end of
the nerve to the other; but when a gland of Drosera is repeatedly
touched or gently pressed, we can actually see a molecular change
proceeding from the gland down the tentacle; though this change is
probably of a very different nature from that in a nerve. Finally, as
so many and such widely different causes excite aggregation, it would
appear that the living matter within the gland-cells is in so unstable
a condition that almost any disturbance suffices to change its
molecular nature, as in the case of certain chemical compounds. And
this change in the glands, whether excited directly, or indirectly by a
stimulus received from other glands, is transmitted from cell to cell,
causing granules of protoplasm either to be actually generated in the
previously limpid fluid or to coalesce and thus to become visible.

Supplementary Observations on the Process of Aggregation in the Roots
of Plants.

It will hereafter be seen that a weak solution of the carbonate of
ammonia induces aggregation in the cells of the roots of Drosera; and
this led me to make a few trials on the roots of other plants. I dug up
in the latter part of October the first weed which I met with, viz.
Euphorbia peplus, being care- [page 64] ful not to injure the roots;
these were washed and placed in a little solution of one part of
carbonate of ammonia to 146 of water. In less than one minute I saw a
cloud travelling from cell to cell up the roots, with wonderful
rapidity. After from 8 m. to 9 m. the fine granules, which caused this
cloudy appearance, became aggregated towards the extremities of the
roots into quadrangular masses of brown matter; and some of these soon
changed their forms and became spherical. Some of the cells, however,
remained unaffected. I repeated the experiment with another plant of
the same species, but before I could get the specimen into focus under
the microscope, clouds of granules and quadrangular masses of reddish
and brown matter were formed, and had run far up all the roots. A fresh
root was now left for 18 hrs. in a drachm of a solution of one part of
the carbonate to 437 of water, so that it received 1/8 of a grain, or
2.024 mg. When examined, the cells of all the roots throughout their
whole length contained aggregated masses of reddish and brown matter.
Before making these experiments, several roots were closely examined,
and not a trace of the cloudy appearance or of the granular masses
could be seen in any of them. Roots were also immersed for 35 m. in a
solution of one part of carbonate of potash to 218 of water; but this
salt produced no effect.

I may here add that thin slices of the stem of the Euphorbia were
placed in the same solution, and the cells which were green instantly
became cloudy, whilst others which were before colourless were clouded
with brown, owing to the formation of numerous granules of this tint. I
have also seen with various kinds of leaves, left for some time in a
solution of carbonate of ammonia, that the grains of chlorophyll ran
together and partially coalesced; and this seems to be a form of
aggregation.

Plants of duck-weed (Lemna) were left for between 30 m. and 45 m. in a
solution of one part of this same salt to 146 of water, and three of
their roots were then examined. In two of them, all the cells which had
previously contained only limpid fluid now included little green
spheres. After from 1 1/2 hr. to 2 hrs. similar spheres appeared in the
cells on the borders of the leaves; but whether the ammonia had
travelled up the roots or had been directly absorbed by the leaves, I
cannot say. As one species, Lemna arrhiza, produces no roots, the
latter alternative is perhaps the most probable. After about 2 1/2 hrs.
some of the little green spheres in the roots were broken up into small
granules which exhibited Brownian movements. Some duck-weed was also
left for 1 hr. 30 m. in a solution of one part of [page 65] carbonate
of potash to 218 of water, and no decided change could be perceived in
the cells of the roots; but when these same roots were placed for 25 m.
in a solution of carbonate of ammonia of the same strength, little
green spheres were formed.

A green marine alga was left for some time in this same solution, but
was very doubtfully affected. On the other hand, a red marine alga,
with finely pinnated fronds, was strongly affected. The contents of the
cells aggregated themselves into broken rings, still of a red colour,
which very slowly and slightly changed their shapes, and the central
spaces within these rings became cloudy with red granular matter. The
facts here given (whether they are new, I know not) indicate that
interesting results would perhaps be gained by observing the action of
various saline solutions and other fluids on the roots of plants. [page
66]




CHAPTER IV.
THE EFFECTS OF HEAT ON THE LEAVES.


Nature of the experiments—Effects of boiling water—Warm water causes
rapid inflection—Water at a higher temperature does not cause immediate
inflection, but does not kill the leaves, as shown by their subsequent
re-expansion and by the aggregation of the protoplasm—A still higher
temperature kills the leaves and coagulates the albuminous contents of
the glands.


In my observations on Drosera rotundifolia, the leaves seemed to be
more quickly inflected over animal substances, and to remain inflected
for a longer period during very warm than during cold weather. I
wished, therefore, to ascertain whether heat alone would induce
inflection, and what temperature was the most efficient. Another
interesting point presented itself, namely, at what degree life was
extinguished; for Drosera offers unusual facilities in this respect,
not in the loss of the power of inflection, but in that of subsequent
re-expansion, and more especially in the failure of the protoplasm to
become aggregated, when the leaves after being heated are immersed in a
solution of carbonate of ammonia.*

* When my experiments on the effects of heat were made, I was not aware
that the subject had been carefully investigated by several observers.
For instance, Sachs is convinced (‘Traité de Botanique,’ 1874, pp. 772,
854) that the most different kinds of plants all perish if kept for 10
m. in water at 45° to 46° Cent., or 113° to 115° Fahr.; and he
concludes that the protoplasm within their cells always coagulates, if
in a damp condition, at a temperature of between 50° and 60° Cent., or
122° to 140° Fahr. Max Schultze and Kühne (as quoted by Dr. Bastian in
‘Contemp. Review,’ 1874, p. 528) “found that the protoplasm of
plant-cells, with which they experimented, was always killed and [[page
67]] altered by a very brief exposure to a temperature of 118 1/2°
Fahr. as a maximum.” As my results are deduced from special phenomena,
namely, the subsequent aggregation of the protoplasm and the
re-expansion of the tentacles, they seem to me worth giving. We shall
find that Drosera resists heat somewhat better than most other plants.
That there should be considerable differences in this respect is not
surprising, considering that some low vegetable organisms grow in hot
springs—cases of which have been collected by Prof. Wyman (‘American
Journal of Science,’ vol. xliv. 1867). Thus, Dr. Hooker found Confervae
in water at 168° Fahr.; Humboldt, at 185° Fahr.; and Descloizeaux, at
208° Fahr.) [page 67]


[My experiments were tried in the following manner. Leaves were cut
off, and this does not in the least interfere with their powers; for
instance, three cut off leaves, with bits of meat placed on them, were
kept in a damp atmosphere, and after 23 hrs. closely embraced the meat
both with their tentacles and blades; and the protoplasm within their
cells was well aggregated. Three ounces of doubly distilled water was
heated in a porcelain vessel, with a delicate thermometer having a long
bulb obliquely suspended in it. The water was gradually raised to the
required temperature by a spirit-lamp moved about under the vessel; and
in all cases the leaves were continually waved for some minutes close
to the bulb. They were then placed in cold water, or in a solution of
carbonate of ammonia. In other cases they were left in the water, which
had been raised to a certain temperature, until it cooled. Again in
other cases the leaves were suddenly plunged into water of a certain
temperature, and kept there for a specified time. Considering that the
tentacles are extremely delicate, and that their coats are very thin,
it seems scarcely possible that the fluid contents of their cells
should not have been heated to within a degree or two of the
temperature of the surrounding water. Any further precautions would, I
think, have been superfluous, as the leaves from age or constitutional
causes differ slightly in their sensitiveness to heat.

It will be convenient first briefly to describe the effects of
immersion for thirty seconds in boiling water. The leaves are rendered
flaccid, with their tentacles bowed backwards, which, as we shall see
in a future chapter, is probably due to their outer surfaces retaining
their elasticity for a longer period than their inner surfaces retain
the power of contraction. The purple fluid within the cells of the
pedicels is rendered finely granular, but there is no true aggregation;
nor does this follow [page 68] when the leaves are subsequently placed
in a solution of carbonate of ammonia. But the most remarkable change
is that the glands become opaque and uniformly white; and this may be
attributed to the coagulation of their albuminous contents.

My first and preliminary experiment consisted in putting seven leaves
in the same vessel of water, and warming it slowly up to the
temperature of 110° Fahr. (43°.3 Cent.); a leaf being taken out as soon
as the temperature rose to 80° (26°.6 Cent.), another at 85°, another
at 90°, and so on. Each leaf, when taken out, was placed in water at
the temperature of my room, and the tentacles of all soon became
slightly, though irregularly, inflected. They were now removed from the
cold water and kept in damp air, with bits of meat placed on their
discs. The leaf which had been exposed to the temperature of 110o
became in 15 m. greatly inflected; and in 2 hrs. every single tentacle
closely embraced the meat. So it was, but after rather longer
intervals, with the six other leaves. It appears, therefore, that the
warm bath had increased their sensitiveness when excited by meat.

I next observed the degree of inflection which leaves underwent within
stated periods, whilst still immersed in warm water, kept as nearly as
possible at the same temperature; but I will here and elsewhere give
only a few of the many trials made. A leaf was left for 10 m. in water
at 100° (37°.7 Cent.), but no inflection occurred. A second leaf,
however, treated in the same manner, had a few of its exterior
tentacles very slightly inflected in 6 m., and several irregularly but
not closely inflected in 10 m. A third leaf, kept in water at 105° to
106° (40°.5 to 41°.1 Cent.), was very moderately inflected in 6 m. A
fourth leaf, in water at 110° (43°.3 Cent.), was somewhat inflected in
4 m., and considerably so in from 6 to 7 m.

Three leaves were placed in water which was heated rather quickly, and
by the time the temperature rose to 115°-116° (46°.1 to 46°.06 Cent.),
all three were inflected. I then removed the lamp, and in a few minutes
every single tentacle was closely inflected. The protoplasm within the
cells was not killed, for it was seen to be in distinct movement; and
the leaves, having been left in cold water for 20 hrs., re-expanded.
Another leaf was immersed in water at 100o (37.7° Cent.), which was
raised to 120° (48°.8 Cent.); and all the tentacles, except the extreme
marginal ones, soon became closely inflected. The leaf was now placed
in cold water, and in 7 hrs. 30 m. it had partly, and in 10 hrs. fully,
re-expanded. On the following morning it was immersed in a weak
solution of carbonate of [page 69] ammonia, and the glands quickly
became black, with strongly marked aggregation in the tentacles,
showing that the protoplasm was alive, and that the glands had not lost
their power of absorption. Another leaf was placed in water at 110o
(43°.3 Cent.) which was raised to 120° (48°.8 Cent.); and every
tentacle, excepting one, was quickly and closely inflected. This leaf
was now immersed in a few drops of a strong solution of carbonate of
ammonia (one part to 109 of water); in 10 m. all the glands became
intensely black, and in 2 hrs. the protoplasm in the cells of the
pedicels was well aggregated. Another leaf was suddenly plunged, and as
usual waved about, in water at 120°, and the tentacles became inflected
in from 2 m. to 3 m., but only so as to stand at right angles to the
disc. The leaf was now placed in the same solution (viz. one part of
carbonate of ammonia to 109 of water, or 4 grs. to 1 oz., which I will
for the future designate as the strong solution), and when I looked at
it again after the interval of an hour, the glands were blackened, and
there was well-marked aggregation. After an additional interval of 4
hrs. the tentacles had become much more inflected. It deserves notice
that a solution as strong as this never causes inflection in ordinary
cases. Lastly a leaf was suddenly placed in water at 125° (51°.6
Cent.), and was left in it until the water cooled; the tentacles were
rendered of a bright red and soon became inflected. The contents of the
cells underwent some degree of aggregation, which in the course of
three hours increased; but the masses of protoplasm did not become
spherical, as almost always occurs with leaves immersed in a solution
of carbonate of ammonia.]

We learn from these cases that a temperature of from 120° to 125°
(48°.8 to 51°.6 Cent.) excites the tentacles into quick movement, but
does not kill the leaves, as shown either by their subsequent
re-expansion or by the aggregation of the protoplasm. We shall now see
that a temperature of 130° (54°.4 Cent.) is too high to cause immediate
inflection, yet does not kill the leaves.

[Experiment 1.—A leaf was plunged, and as in all cases waved about for
a few minutes, in water at 130° (54°.4 Cent.), but there was no trace
of inflection; it was then placed in cold water, and after an interval
of 15 m. very slow movement was [page 70] distinctly seen in a small
mass of protoplasm in one of the cells of a tentacle.* After a few
hours all the tentacles and the blade became inflected.

Experiment 2.—Another leaf was plunged into water at 130o to 131o, and
as before there was no inflection. After being kept in cold water for
an hour, it was placed in the strong solution of ammonia, and in the
course of 55 m. the tentacles were considerably inflected. The glands,
which before had been rendered of a brighter red, were now blackened.
The protoplasm in the cells of the tentacles was distinctly aggregated;
but the spheres were much smaller than those generated in unheated
leaves when subjected to carbonate of ammonia. After an additional 2
hrs. all the tentacles, excepting six or seven, were closely inflected.

Experiment 3.—A similar experiment to the last, with exactly the same
results.

Experiment 4.—A fine leaf was placed in water at 100° (37°.7 Cent.),
which was then raised to 145° (62°.7 Cent.). Soon after immersion,
there was, as might have been expected, strong inflection. The leaf was
now removed and left in cold water; but from having been exposed to so
high a temperature, it never re-expanded.

Experiment 5.—Leaf immersed at 130° (54°.4 Cent.), and the water raised
to 145° (62°.7 Cent.), there was no immediate inflection; it was then
placed in cold water, and after 1 hr. 20 m. some of the tentacles on
one side became inflected. This leaf was now placed in the strong
solution, and in 40 m. all the submarginal tentacles were well
inflected, and the glands blackened. After an additional interval of 2
hrs. 45 m. all the tentacles, except eight or ten, were closely
inflected, with their cells exhibiting a slight degree of aggregation;
but the spheres of protoplasm were very small, and the cells of the
exterior tentacles contained some pulpy or disintegrated brownish
matter.

Experiments 6 and 7.—Two leaves were plunged in water at 135° (57°.2
Cent.) which was raised to 145° (62°.7 Cent.); neither became
inflected. One of these, however, after having been left for 31 m. in
cold water, exhibited some slight inflection, which increased after an
additional interval of 1 hr. 45 m., until

* Sachs states (‘Traité de Botanique,’ 1874, p. 855) that the movements
of the protoplasm in the hairs of a Cucurbita ceased after they were
exposed for 1 m. in water to a temperature of 47° to 48° Cent., or 117°
to 119° Fahr. [page 71]


all the tentacles, except sixteen or seventeen, were more or less
inflected; but the leaf was so much injured that it never re-expanded.
The other leaf, after having been left for half an hour in cold water,
was put into the strong solution, but no inflection ensued; the glands,
however, were blackened, and in some cells there was a little
aggregation, the spheres of protoplasm being extremely small; in other
cells, especially in the exterior tentacles, there was much
greenish-brown pulpy matter.

Experiment 8.—A leaf was plunged and waved about for a few minutes in
water at 140° (60° Cent.), and was then left for half an hour in cold
water, but there was no inflection. It was now placed in the strong
solution, and after 2 hrs. 30 m. the inner submarginal tentacles were
well inflected, with their glands blackened, and some imperfect
aggregation in the cells of the pedicels. Three or four of the glands
were spotted with the white porcelain-like structure, like that
produced by boiling water. I have seen this result in no other instance
after an immersion of only a few minutes in water at so low a
temperature as 140°, and in only one leaf out of four, after a similar
immersion at a temperature of 145° Fahr. On the other hand, with two
leaves, one placed in water at 145° (62°.7 Cent.), and the other in
water at 140° (60° Cent.), both being left therein until the water
cooled, the glands of both became white and porcelain-like. So that the
duration of the immersion is an important element in the result.

Experiment 9.—A leaf was placed in water at 140° (60° Cent.), which was
raised to 150° (65°.5 Cent.); there was no inflection; on the contrary,
the outer tentacles were somewhat bowed backwards. The glands became
like porcelain, but some of them were a little mottled with purple. The
bases of the glands were often more affected than their summits. This
leaf having been left in the strong solution did not undergo any
inflection or aggregation.

Experiment 10.—A leaf was plunged in water at 150° to 150 1/2° (65°.5
Cent.); it became somewhat flaccid, with the outer tentacles slightly
reflexed, and the inner ones a little bent inwards, but only towards
their tips; and this latter fact shows that the movement was not one of
true inflection, as the basal part alone normally bends. The tentacles
were as usual rendered of a very bright red, with the glands almost
white like porcelain, yet tinged with pink. The leaf having been placed
in the strong solution, the cell-contents of the tentacles became of a
muddy-brown, with no trace of aggregation. [page 72]

Experiment 11.—A leaf was immersed in water at 145° (62°.7 Cent.),
which was raised to 156° (68°.8 Cent.). The tentacles became bright red
and somewhat reflexed, with almost all the glands like porcelain; those
on the disc being still pinkish, those near the margin quite white. The
leaf being placed as usual first in cold water and then in the strong
solution, the cells in the tentacles became of a muddy greenish brown,
with the protoplasm not aggregated. Nevertheless, four of the glands
escaped being rendered like porcelain, and the pedicels of these glands
were spirally curled, like a French horn, towards their upper ends; but
this can by no means be considered as a case of true inflection. The
protoplasm within the cells of the twisted portions was aggregated into
distinct though excessively minute purple spheres. This case shows
clearly that the protoplasm, after having been exposed to a high
temperature for a few minutes, is capable of aggregation when
afterwards subjected to the action of carbonate of ammonia, unless the
heat has been sufficient to cause coagulation.]

Concluding Remarks.—As the hair-like tentacles are extremely thin and
have delicate walls, and as the leaves were waved about for some
minutes close to the bulb of the thermometer, it seems scarcely
possible that they should not have been raised very nearly to the
temperature which the instrument indicated. From the eleven last
observations we see that a temperature of 130° (54°.4 Cent.) never
causes the immediate inflection of the tentacles, though a temperature
from 120° to 125° (48°.8 to 51°.6 Cent.) quickly produces this effect.
But the leaves are paralysed only for a time by a temperature of 130°,
as afterwards, whether left in simple water or in a solution of
carbonate of ammonia, they become inflected and their protoplasm
undergoes aggregation. This great difference in the effects of a higher
and lower temperature may be compared with that from immersion in
strong and weak solutions of the salts of ammonia; for the former do
not excite movement, whereas the latter act energetically. A temporary
suspension of the [page 73] power of movement due to heat is called by
Sachs* heat-rigidity; and this in the case of the sensitive-plant
(Mimosa) is induced by its exposure for a few minutes to humid air,
raised to 120°-122° Fahr., or 49° to 50° Cent. It deserves notice that
the leaves of Drosera, after being immersed in water at 130° Fahr., are
excited into movement by a solution of the carbonate so strong that it
would paralyse ordinary leaves and cause no inflection.

The exposure of the leaves for a few minutes even to a temperature of
145° Fahr. (62°.7 Cent.) does not always kill them; as when afterwards
left in cold water, or in a strong solution of carbonate of ammonia,
they generally, though not always, become inflected; and the protoplasm
within their cells undergoes aggregation, though the spheres thus
formed are extremely small, with many of the cells partly filled with
brownish muddy matter. In two instances, when leaves were immersed in
water, at a lower temperature than 130° (54°.4 Cent.), which was then
raised to 145° (62°.7 Cent.), they became during the earlier period of
immersion inflected, but on being afterwards left in cold water were
incapable of re-expansion. Exposure for a few minutes to a temperature
of 145o sometimes causes some few of the more sensitive glands to be
speckled with the porcelain-like appearance; and on one occasion this
occurred at a temperature of 140° (60° Cent.). On another occasion,
when a leaf was placed in water at this temperature of only 140o, and
left therein till the water cooled, every gland became like porcelain.
Exposure for a few minutes to a temperature of 150° (65°.5 Cent.)
generally produces this effect, yet many glands retain a

* ‘Traité de Bot.’ 1874, p. 1034. [page 74]


pinkish colour, and many present a speckled appearance. This high
temperature never causes true inflection; on the contrary, the
tentacles commonly become reflexed, though to a less degree than when
immersed in boiling water; and this apparently is due to their passive
power of elasticity. After exposure to a temperature of 150° Fahr., the
protoplasm, if subsequently subjected to carbonate of ammonia, instead
of undergoing aggregation, is converted into disintegrated or pulpy
discoloured matter. In short, the leaves are generally killed by this
degree of heat; but owing to differences of age or constitution, they
vary somewhat in this respect. In one anomalous case, four out of the
many glands on a leaf, which had been immersed in water raised to 156°
(68°.8 Cent.), escaped being rendered porcellanous;* and the protoplasm
in the cells close beneath these glands underwent some slight, though
imperfect, degree of aggregation.

Finally, it is a remarkable fact that the leaves of Drosera
rotundifolia, which flourishes on bleak upland moors throughout Great
Britain, and exists (Hooker) within the Arctic Circle, should be able
to withstand for even a short time immersion in water heated to a
temperature of 145°.**

It may be worth adding that immersion in cold

* As the opacity and porcelain-like appearance of the glands is
probably due to the coagulation of the albumen, I may add, on the
authority of Dr. Burdon Sanderson, that albumen coagulates at about
155o, but, in presence of acids, the temperature of coagulation is
lower. The leaves of Drosera contain an acid, and perhaps a difference
in the amount contained may account for the slight differences in the
results above recorded.


** It appears that cold-blooded animals are, as might have been
expected, far more sensitive to an increase of temperature than is
Drosera. Thus, as I hear from Dr. Burdon Sanderson, a frog begins to be
distressed in water at a temperature of only 85° Fahr. At 95° the
muscles become rigid, and the animal dies in a stiffened condition.
[page 75]


water does not cause any inflection: I suddenly placed four leaves,
taken from plants which had been kept for several days at a high
temperature, generally about 75° Fahr. (23°.8 Cent.), in water at 45°
(7°.2 Cent.), but they were hardly at all affected; not so much as some
other leaves from the same plants, which were at the same time immersed
in water at 75°; for these became in a slight degree inflected. [page
76]




CHAPTER V.
THE EFFECTS OF NON-NITROGENOUS AND NITROGENOUS ORGANIC FLUIDS ON THE
LEAVES.


Non-nitrogenous fluids—Solutions of gum arabic—Sugar—Starch—Diluted
alcohol—Olive oil— Infusion and decoction of tea—Nitrogenous
fluids—Milk—Urine—Liquid albumen—Infusion of raw meat—Impure
mucus—Saliva—Solution of isinglass—Difference in the action of these
two sets of fluids—Decoction of green peas—Decoction and infusion of
cabbage—Decoction of grass leaves.


When, in 1860, I first observed Drosera, and was led to believe that
the leaves absorbed nutritious matter from the insects which they
captured, it seemed to me a good plan to make some preliminary trials
with a few common fluids, containing and not containing nitrogenous
matter; and the results are worth giving.

In all the following cases a drop was allowed to fall from the same
pointed instrument on the centre of the leaf; and by repeated trials
one of these drops was ascertained to be on an average very nearly half
a minim, or 1/960 of a fluid ounce, or .0295 ml. But these measurements
obviously do not pretend to any strict accuracy; moreover, the drops of
the viscid fluids were plainly larger than those of water. Only one
leaf on the same plant was tried, and the plants were collected from
two distant localities. The experiments were made during August and
September. In judging of the effects, one caution is necessary: if a
drop of any adhesive fluid is placed on an old or feeble leaf, the
glands of which have ceased to secrete copiously, the drop sometimes
dries up, especially if the plant [page 77] is kept in a room, and some
of the central and submarginal tentacles are thus drawn together,
giving to them the false appearance of having become inflected. This
sometimes occurs with water, as it is rendered adhesive by mingling
with the viscid secretion. Hence the only safe criterion, and to this
alone I have trusted, is the bending inwards of the exterior tentacles,
which have not been touched by the fluid, or at most only at their
bases. In this case the movement is wholly due to the central glands
having been stimulated by the fluid, and transmitting a motor impulse
to the exterior tentacles. The blade of the leaf likewise often curves
inwards, in the same manner as when an insect or bit of meat is placed
on the disc. This latter movement is never caused, as far as I have
seen, by the mere drying up of an adhesive fluid and the consequent
drawing together of the tentacles.

First for the non-nitrogenous fluids. As a preliminary trial, drops of
distilled water were placed on between thirty and forty leaves, and no
effect whatever was produced; nevertheless, in some other and rare
cases, a few tentacles became for a short time inflected; but this may
have been caused by the glands having been accidentally touched in
getting the leaves into a proper position. That water should produce no
effect might have been anticipated, as otherwise the leaves would have
been excited into movement by every shower of rain.

[Gum arabic.—Solutions of four degrees of strength were made; one of
six grains to the ounce of water (one part to 73); a second rather
stronger, yet very thin; a third moderately thick, and a fourth so
thick that it would only just drop from a pointed instrument. These
were tried on fourteen leaves; the drops being left on the discs from
24 hrs. to 44 hrs.; generally about [page 78] 30 hrs. Inflection was
never thus caused. It is necessary to try pure gum arabic, for a friend
tried a solution bought ready prepared, and this caused the tentacles
to bend; but he afterwards ascertained that it contained much animal
matter, probably glue.

Sugar.—Drops of a solution of white sugar of three strengths (the
weakest containing one part of sugar to 73 of water) were left on
fourteen leaves from 32 hrs. to 48 hrs.; but no effect was produced.

Starch.—A mixture about as thick as cream was dropped on six leaves and
left on them for 30 hrs., no effect being produced. I am surprised at
this fact, as I believe that the starch of commerce generally contains
a trace of gluten, and this nitrogenous substance causes inflection, as
we shall see in the next chapter.

Alcohol, Diluted.—One part of alcohol was added to seven of water, and
the usual drops were placed on the discs of three leaves. No inflection
ensued in the course of 48 hrs. To ascertain whether these leaves had
been at all injured, bits of meat were placed on them, and after 24
hrs. they were closely inflected. I also put drops of sherry-wine on
three other leaves; no inflection was caused, though two of them seemed
somewhat injured. We shall hereafter see that cut off leaves immersed
in diluted alcohol of the above strength do not become inflected.

Olive Oil.—drops were placed on the discs of eleven leaves, and no
effect was produced in from 24 hrs. to 48 hrs. Four of these leaves
were then tested by bits of meat on their discs, and three of them were
found after 24 hrs. with all their tentacles and blades closely
inflected, whilst the fourth had only a few tentacles inflected. It
will, however, be shown in a future place, that cut off leaves immersed
in olive oil are powerfully affected.

Infusion and Decoction of Tea.—Drops of a strong infusion and
decoction, as well as of a rather weak decoction, of tea were placed on
ten leaves, none of which became inflected. I afterwards tested three
of them by adding bits of meat to the drops which still remained on
their discs, and when I examined them after 24 hrs. they were closely
inflected. The chemical principle of tea, namely theine, was
subsequently tried and produced no effect. The albuminous matter which
the leaves must originally have contained, no doubt, had been rendered
insoluble by their having been completely dried.]

We thus see that, excluding the experiments with water, sixty-one
leaves were tried with drops of the [page 79] above-named
non-nitrogenous fluids; and the tentacles were not in a single case
inflected.

[With respect to nitrogenous fluids, the first which came to hand were
tried. The experiments were made at the same time and in exactly the
same manner as the foregoing. As it was immediately evident that these
fluids produced a great effect, I neglected in most cases to record how
soon the tentacles became inflected. But this always occurred in less
than 24 hrs.; whilst the drops of non-nitrogenous fluids which produced
no effect were observed in every case during a considerably longer
period.

Milk.—Drops were placed on sixteen leaves, and the tentacles of all, as
well as the blades of several, soon became greatly inflected. The
periods were recorded in only three cases, namely, with leaves on which
unusually small drops had been placed. Their tentacles were somewhat
inflected in 45 m.; and after 7 hrs. 45 m. the blades of two were so
much curved inwards that they formed little cups enclosing the drops.
These leaves re-expanded on the third day. On another occasion the
blade of a leaf was much inflected in 5 hrs. after a drop of milk had
been placed on it.

Human Urine.—Drops were placed on twelve leaves, and the tentacles of
all, with a single exception, became greatly inflected. Owing, I
presume, to differences in the chemical nature of the urine on
different occasions, the time required for the movements of the
tentacles varied much, but was always effected in under 24 hrs. In two
instances I recorded that all the exterior tentacles were completely
inflected in 17 hrs., but not the blade of the leaf. In another case
the edges of a leaf, after 25 hrs. 30 m., became so strongly inflected
that it was converted into a cup. The power of urine does not lie in
the urea, which, as we shall hereafter see, is inoperative.

Albumen (fresh from a hen’s egg), placed on seven leaves, caused the
tentacles of six of them to be well inflected. In one case the edge of
the leaf itself became much curled in after 20 hrs. The one leaf which
was unaffected remained so for 26 hrs., and was then treated with a
drop of milk, and this caused the tentacles to bend inwards in 12 hrs.

Cold Filtered Infusion of Raw Meat.—This was tried only on a single
leaf, which had most of its outer tentacles and the blade inflected in
19 hrs. During subsequent years, I repeatedly used this infusion to
test leaves which had been experimented [page 80] on with other
substances, and it was found to act most energetically, but as no exact
account of these trials was kept, they are not here introduced.

Mucus.—Thick and thin mucus from the bronchial tubes, placed on three
leaves, caused inflection. A leaf with thin mucus had its marginal
tentacles and blade somewhat curved inward in 5 hrs. 30 m., and greatly
so in 20 hrs. The action of this fluid no doubt is due either to the
saliva or to some albuminous matter* mingled with it, and not, as we
shall see in the next chapter, to mucin or the chemical principle of
mucus.

Saliva.—Human saliva, when evaporated, yields** from 1.14 to 1.19 per
cent. of residue; and this yields 0.25 per cent. of ashes, so that the
proportion of nitrogenous matter which saliva contains must be small.
Nevertheless, drops placed on the discs of eight leaves acted on them
all. In one case all the exterior tentacles, excepting nine, were
inflected in 19 hrs. 30 m.; in another case a few became so in 2 hrs.,
and after 7 hrs. 30 m. all those situated near where the drop lay, as
well as the blade, were acted on. Since making these trials, I have
many scores of times just touched glands with the handle of my scalpel
wetted with saliva, to ascertain whether a leaf was in an active
condition; for this was shown in the course of a few minutes by the
bending inwards of the tentacles. The edible nest of the Chinese
swallow is formed of matter secreted by the salivary glands; two grains
were added to one ounce of distilled water (one part to 218), which was
boiled for several minutes, but did not dissolve the whole. The
usual-sized drops were placed on three leaves, and these in 1 hr. 30 m.
were well, and in 2 hrs. 15 m. closely, inflected.

Isinglass.—Drops of a solution about as thick as milk, and of a still
thicker solution, were placed on eight leaves, and the tentacles of all
became inflected. In one case the exterior tentacles were well curved
in after 6 hrs. 30 m., and the blade of the leaf to a partial extent
after 24 hrs. As saliva acted so efficiently, and yet contains so small
a proportion of nitrogenous matter, I tried how small a quantity of
isinglass would act. One part was dissolved in 218 parts of distilled
water, and drops were placed on four leaves. After 5 hrs. two of these
were considerably and two moderately inflected; after 22 hrs. the
former were greatly and the latter much more inflected. In the course
of 48 hrs.

* Mucus from the air-passages is said in Marshall, ‘Outlines of
Physiology,’ vol. ii. 1867, p. 364, to contain some albumen.


** Müller’s ‘Elements of Physiology,’ Eng. Trans. vol. i., p. 514.
[page 81]


from the time when the drops were placed on the leaves, all four had
almost re-expanded. They were then given little bits of meat, and these
acted more powerfully than the solution. One part of isinglass was next
dissolved in 437 of water; the fluid thus formed was so thin that it
could not be distinguished from pure water. The usual-sized drops were
placed on seven leaves, each of which thus received 1/960 of a grain
(.0295 mg.). Three of them were observed for 41 hrs., but were in no
way affected; the fourth and fifth had two or three of their exterior
tentacles inflected after 18 hrs.; the sixth had a few more; and the
seventh had in addition the edge of the leaf just perceptibly curved
inwards. The tentacles of the four latter leaves began to re-expand
after an additional interval of only 8 hrs. Hence the 1/960 of a grain
of isinglass is sufficient to affect very slightly the more sensitive
or active leaves. On one of the leaves, which had not been acted on by
the weak solution, and on another, which had only two of its tentacles
inflected, drops of the solution as thick as milk were placed; and next
morning, after an interval of 16 hrs., both were found with all their
tentacles strongly inflected.]

Altogether I experimented on sixty-four leaves with the above
nitrogenous fluids, the five leaves tried only with the extremely weak
solution of isinglass not being included, nor the numerous trials
subsequently made, of which no exact account was kept. Of these
sixty-four leaves, sixty-three had their tentacles and often their
blades well inflected. The one which failed was probably too old and
torpid. But to obtain so large a proportion of successful cases, care
must be taken to select young and active leaves. Leaves in this
condition were chosen with equal care for the sixty-one trials with
non-nitrogenous fluids (water not included); and we have seen that not
one of these was in the least affected. We may therefore safely
conclude that in the sixty-four experiments with nitrogenous fluids the
inflection of the exterior tentacles was due to the absorption of [page
82] nitrogenous matter by the glands of the tentacles on the disc.

Some of the leaves which were not affected by the non-nitrogenous
fluids were, as above stated, immediately afterwards tested with bits
of meat, and were thus proved to be in an active condition. But in
addition to these trials, twenty-three of the leaves, with drops of
gum, syrup, or starch, still lying on their discs, which had produced
no effect in the course of between 24 hrs. and 48 hrs., were then
tested with drops of milk, urine, or albumen. Of the twenty-three
leaves thus treated, seventeen had their tentacles, and in some cases
their blades, well inflected; but their powers were somewhat impaired,
for the rate of movement was decidedly slower than when fresh leaves
were treated with these same nitrogenous fluids. This impairment, as
well as the insensibility of six of the leaves, may be attributed to
injury from exosmose, caused by the density of the fluids placed on
their discs.

[The results of a few other experiments with nitrogenous fluids may be
here conveniently given. Decoctions of some vegetables, known to be
rich in nitrogen, were made, and these acted like animal fluids. Thus,
a few green peas were boiled for some time in distilled water, and the
moderately thick decoction thus made was allowed to settle. Drops of
the superincumbent fluid were placed on four leaves, and when these
were looked at after 16 hrs., the tentacles and blades of all were
found strongly inflected. I infer from a remark by Gerhardt* that
legumin is present in peas “in combination with an alkali, forming an
incoagulable solution,” and this would mingle with boiling water. I may
mention, in relation to the above and following experiments, that
according to Schiff** certain forms of albumen

* Watts’ ‘Dictionary of Chemistry,’ vol. iii., p. 568.


** ‘Leçons sur la Phys. de la Digestion,’ tom. i, p. 379; tom. ii. pp.
154, 166, on legumin. [page 83]


exist which are not coagulated by boiling water, but are converted into
soluble peptones.

On three occasions chopped cabbage-leaves* were boiled in distilled
water for 1 hr. or for 1 1/4 hr.; and by decanting the decoction after
it had been allowed to rest, a pale dirty green fluid was obtained. The
usual-sized drops were placed on thirteen leaves. Their tentacles and
blades were inflected after 4 hrs. to a quite extraordinary degree.
Next day the protoplasm within the cells of the tentacles was found
aggregated in the most strongly marked manner. I also touched the
viscid secretion round the glands of several tentacles with minute
drops of the decoction on the head of a small pin, and they became well
inflected in a few minutes. The fluid proving so powerful, one part was
diluted with three of water, and drops were placed on the discs of five
leaves; and these next morning were so much acted on that their blades
were completely doubled over. We thus see that a decoction of
cabbage-leaves is nearly or quite as potent as an infusion of raw meat.

About the same quantity of chopped cabbage-leaves and of distilled
water, as in the last experiment, were kept in a vessel for 20 hrs. in
a hot closet, but not heated to near the boiling-point. Drops of this
infusion were placed on four leaves. One of these, after 23 hrs., was
much inflected; a second slightly; a third had only the submarginal
tentacles inflected; and the fourth was not at all affected. The power
of this infusion is therefore very much less than that of the
decoction; and it is clear that the immersion of cabbage-leaves for an
hour in water at the boiling temperature is much more efficient in
extracting matter which excites Drosera than immersion during many
hours in warm water. Perhaps the contents of the cells are protected
(as Schiff remarks with respect to legumin) by the walls being formed
of cellulose, and that until these are ruptured by boiling-water, but
little of the contained albuminous matter is dissolved. We know from
the strong odour of cooked cabbage-leaves that boiling water produces
some chemical change in them, and that they are thus rendered far more
digestible and nutritious to man. It is therefore an interesting

* The leaves of young plants, before the heart is formed, such as were
used by me, contain 2.1 per cent. of albuminous matter, and the outer
leaves of mature plants 1.6 per cent. Watts’ ‘Dictionary of Chemistry,’
vol. i. p. 653. [page 84]


fact that water at this temperature extracts matter from them which
excites Drosera to an extraordinary degree.

Grasses contain far less nitrogenous matter than do peas or cabbages.
The leaves and stalks of three common kinds were chopped and boiled for
some time in distilled water. Drops of this decoction (after having
stood for 24 hrs.) were placed on six leaves, and acted in a rather
peculiar manner, of which other instances will be given in the seventh
chapter on the salts of ammonia. After 2 hrs. 30 m. four of the leaves
had their blades greatly inflected, but not their exterior tentacles;
and so it was with all six leaves after 24 hrs. Two days afterwards the
blades, as well as the few submarginal tentacles which had been
inflected, all re-expanded; and much of the fluid on their discs was by
this time absorbed. It appears that the decoction strongly excites the
glands on the disc, causing the blade to be quickly and greatly
inflected; but that the stimulus, differently from what occurs in
ordinary cases, does not spread, or only in a feeble degree, to the
exterior tentacles.

I may here add that one part of the extract of belladonna (procured
from a druggist) was dissolved in 437 of water, and drops were placed
on six leaves. Next day all six were somewhat inflected, and after 48
hrs. were completely re-expanded. It was not the included atropine
which produced this effect, for I subsequently ascertained that it is
quite powerless. I also procured some extract of hyoscyamus from three
shops, and made infusions of the same strength as before. Of these
three infusions, only one acted on some of the leaves, which were
tried. Though druggists believe that all the albumen is precipitated in
the preparation of these drugs, I cannot doubt that some is
occasionally retained; and a trace would be sufficient to excite the
more sensitive leaves of Drosera. [page 85]




CHAPTER VI.
THE DIGESTIVE POWER OF THE SECRETION OF DROSERA.


The secretion rendered acid by the direct and indirect excitement of
the glands—Nature of the acid—Digestible substances—Albumen, its
digestion arrested by alkalies, recommences by the addition of an
acid—Meat—Fibrin—Syntonin—Areolar tissue—Cartilage—Fibro-cartilage—
Bone—Enamel and dentine—Phosphate of lime—Fibrous basis of
bone—Gelatine—Chondrin— Milk, casein and
cheese—Gluten—Legumin—Pollen—Globulin—Haematin—Indigestible
substances—Epidermic productions—Fibro-elastic
tissue—Mucin—Pepsin—Urea—Chitine— Cellulose—Gun-cotton—Chlorophyll—Fat
and oil—Starch—Action of the secretion on living seeds—Summary and
concluding remarks.


As we have seen that nitrogenous fluids act very differently on the
leaves of Drosera from non-nitrogenous fluids, and as the leaves remain
clasped for a much longer time over various organic bodies than over
inorganic bodies, such as bits of glass, cinder, wood, &c., it becomes
an interesting inquiry, whether they can only absorb matter already in
solution, or render it soluble,—that is, have the power of digestion.
We shall immediately see that they certainly have this power, and that
they act on albuminous compounds in exactly the same manner as does the
gastric juice of mammals; the digested matter being afterwards
absorbed. This fact, which will be clearly proved, is a wonderful one
in the physiology of plants. I must here state that I have been aided
throughout all my later experiments by many valuable suggestions and
assistance given me with the greatest kindness by Dr. Burdon Sanderson.
[page 86]

It may be well to premise for the sake of any reader who knows nothing
about the digestion of albuminous compounds by animals that this is
effected by means of a ferment, pepsin, together with weak hydrochloric
acid, though almost any acid will serve. Yet neither pepsin nor an acid
by itself has any such power.* We have seen that when the glands of the
disc are excited by the contact of any object, especially of one
containing nitrogenous matter, the outer tentacles and often the blade
become inflected; the leaf being thus converted into a temporary cup or
stomach. At the same time the discal glands secrete more copiously, and
the secretion becomes acid. Moreover, they transmit some influence to
the glands of the exterior tentacles, causing them to pour forth a more
copious secretion, which also becomes acid or more acid than it was
before.

As this result is an important one, I will give the evidence. The
secretion of many glands on thirty leaves, which had not been in any
way excited, was tested with litmus paper; and the secretion of
twenty-two of these leaves did not in the least affect the colour,
whereas that of eight caused an exceedingly feeble and sometimes
doubtful tinge of red. Two other old leaves, however, which appeared to
have been inflected several times, acted much more decidedly on the
paper. Particles of clean glass were then placed on five of the leaves,
cubes of albumen on six, and bits of raw meat on three, on none of
which was the secretion at this time in the least acid. After an
interval of 24 hrs., when almost all the tentacles on

* It appears, however, according to Schiff, and contrary to the opinion
of some physiologists, that weak hydrochloric dissolves, though slowly,
a very minute quantity of coagulated albumen. Schiff, ‘Phys. de la
Digestion,’ tom. ii. 1867, p. 25. [page 87]


these fourteen leaves had become more or less inflected, I again tested
the secretion, selecting glands which had not as yet reached the centre
or touched any object, and it was now plainly acid. The degree of
acidity of the secretion varied somewhat on the glands of the same
leaf. On some leaves, a few tentacles did not, from some unknown cause,
become inflected, as often happens; and in five instances their
secretion was found not to be in the least acid; whilst the secretion
of the adjoining and inflected tentacles on the same leaf was decidedly
acid. With leaves excited by particles of glass placed on the central
glands, the secretion which collects on the disc beneath them was much
more strongly acid than that poured forth from the exterior tentacles,
which were as yet only moderately inflected. When bits of albumen (and
this is naturally alkaline), or bits of meat were placed on the disc,
the secretion collected beneath them was likewise strongly acid. As raw
meat moistened with water is slightly acid, I compared its action on
litmus paper before it was placed on the leaves, and afterwards when
bathed in the secretion; and there could not be the least doubt that
the latter was very much more acid. I have indeed tried hundreds of
times the state of the secretion on the discs of leaves which were
inflected over various objects, and never failed to find it acid. We
may, therefore, conclude that the secretion from unexcited leaves,
though extremely viscid, is not acid or only slightly so, but that it
becomes acid, or much more strongly so, after the tentacles have begun
to bend over any inorganic or organic object; and still more strongly
acid after the tentacles have remained for some time closely clasped
over any object.

I may here remind the reader that the secretion [page 88] appears to be
to a certain extent antiseptic, as it checks the appearance of mould
and infusoria, thus preventing for a time the discoloration and decay
of such substances as the white of an egg, cheese, &c. It therefore
acts like the gastric juice of the higher animals, which is known to
arrest putrefaction by destroying the microzymes.

[As I was anxious to learn what acid the secretion contained, 445
leaves were washed in distilled water, given me by Prof. Frankland; but
the secretion is so viscid that it is scarcely possible to scrape or
wash off the whole. The conditions were also unfavourable, as it was
late in the year and the leaves were small. Prof. Frankland with great
kindness undertook to test the fluid thus collected. The leaves were
excited by clean particles of glass placed on them 24 hrs. previously.
No doubt much more acid would have been secreted had the leaves been
excited by animal matter, but this would have rendered the analysis
more difficult. Prof. Frankland informs me that the fluid contained no
trace of hydrochloric, sulphuric, tartaric, oxalic, or formic acids.
This having been ascertained, the remainder of the fluid was evaporated
nearly to dryness, and acidified with sulphuric acid; it then evolved
volatile acid vapour, which was condensed and digested with carbonate
of silver. “The weight of the silver salt thus produced was only .37
gr., much too small a quantity for the accurate determination of the
molecular weight of the acid. The number obtained, however,
corresponded nearly with that of propionic acid; and I believe that
this, or a mixture of acetic and butyric acids, were present in the
liquid. The acid doubtless belongs to the acetic or fatty series.”

Prof. Frankland, as well as his assistant, observed (and this is an
important fact) that the fluid, “when acidified with sulphuric acid,
emitted a powerful odour like that of pepsin.” The leaves from which
the secretion had been washed were also sent to Prof. Frankland; they
were macerated for some hours, then acidified with sulphuric acid and
distilled, but no acid passed over. Therefore the acid which fresh
leaves contain, as shown by their discolouring litmus paper when
crushed, must be of a different nature from that present in the
secretion. Nor was any odour of pepsin emitted by them. [page 89]

Although it has long been known that pepsin with acetic acid has the
power of digesting albuminous compounds, it appeared advisable to
ascertain whether acetic acid could be replaced, without the loss of
digestive power, by the allied acids which are believed to occur in the
secretion of Drosera, namely, propionic, butyric, or valerianic. Dr.
Burdon Sanderson was so kind as to make for me the following
experiments, the results of which are valuable, independently of the
present inquiry. Prof. Frankland supplied the acids.

“1. The purpose of the following experiments was to determine the
digestive activity of liquids containing pepsin, when acidulated with
certain volatile acids belonging to the acetic series, in comparison
with liquids acidulated with hydrochloric acid, in proportion similar
to that in which it exists in gastric juice.

“2. It has been determined empirically that the best results are
obtained in artificial digestion when a liquid containing two per
thousand of hydrochloric acid gas by weight is used. This corresponds
to about 6.25 cubic centimetres per litre of ordinary strong
hydrochloric acid. The quantities of propionic, butyric, and valerianic
acids respectively which are required to neutralise as much base as
6.25 cubic centimetres of HCl, are in grammes 4.04 of propionic acid,
4.82 of butyric acid, and 5.68 of valerianic acid. It was therefore
judged expedient, in comparing the digestive powers of these acids with
that of hydrochloric acid, to use them in these proportions.

“3. Five hundred cub. cent. of a liquid containing about 8 cub. cent.
of a glycerine extract of the mucous membrane of the stomach of a dog
killed during digestion having been prepared, 10 cub. cent. of it were
evaporated and dried at 110o. This quantity yielded 0.0031 of residue.

“4. Of this liquid four quantities were taken which were severally
acidulated with hydrochloric, propionic, butyric, and valerianic acids,
in the proportions above indicated. Each liquid was then placed in a
tube, which was allowed to float in a water bath, containing a
thermometer which indicated a temperature of 38° to 40° Cent. Into
each, a quantity of unboiled fibrin was introduced, and the whole
allowed to stand for four hours, the temperature being maintained
during the whole time, and care being taken that each contained
throughout an excess of fibrin. At the end of the period each liquid
was filtered. Of the filtrate, which of course contained as much of the
fibrin as had been digested during the four hours, [page 90] 10 cub.
cent. were measured out and evaporated, and dried at 110° as before.
The residues were respectively—

“In the liquid containing hydrochloric acid 0.4079 ” ” propionic acid
0.0601 ” ” butyric acid 0.1468 ” ” valerianic acid 0.1254

“Hence, deducting from each of these the above-mentioned residue, left
when the digestive liquid itself was evaporated, viz. 0.0031, we have,

“For propionic acid 0.0570 ” butyric acid 0.1437 ” valerianic acid
0.1223

as compared with 0.4048 for hydrochloric acid; these several numbers
expressing the quantities of fibrin by weight digested in presence of
equivalent quantities of the respective acids under identical
conditions.

“The results of the experiment may be stated thus:—If 100 represent the
digestive power of a liquid containing pepsin with the usual proportion
of hydrochloric acid, 14.0, 35.4, and 30.2, will represent respectively
the digestive powers of the three acids under investigation.

“5. In a second experiment in which the procedure was in every respect
the same, excepting that all the tubes were plunged into the same
water-bath, and the residues dried at 115o C., the results were as
follows:—

“Quantity of fibrin dissolved in four hours by 10 cub. cent. of the
liquid:—

“Propionic acid 0.0563 Butyric acid 0.0835 Valerianic acid 0.0615

“The quantity digested by a similar liquid containing hydrochloric acid
was 0.3376. Hence, taking this as 100, the following numbers represent
the relative quantities digested by the other acids:—

“Propionic acid 16.5 Butyric acid 24.7 Valerianic acid 16.1

“6. A third experiment of the same kind gave: [page 91]

“Quantity of fibrin digested in four hours by 10 cub. cent. of the
liquid:—

“Hydrochloric acid 0.2915 Propionic acid 0.1490 Butyric acid 0.1044
Valerianic acid 0.0520

“Comparing, as before, the three last numbers with the first taken as
100, the digestive power of propionic acid is represented by 16.8; that
of butyric acid by 35.8; and that of valerianic by 17.8.

“The mean of these three sets of observations (hydrochloric acid being
taken as 100) gives for

“Propionic acid 15.8 Butyric acid 32.0 Valerianic acid 21.4

“7. A further experiment was made to ascertain whether the digestive
activity of butyric acid (which was selected as being apparently the
most efficacious) was relatively greater at ordinary temperatures than
at the temperature of the body. It was found that whereas 10 cub. cent.
of a liquid containing the ordinary proportion of hydrochloric acid
digested 0.1311 gramme, a similar liquid prepared with butyric acid
digested 0.0455 gramme of fibrin.

“Hence, taking the quantities digested with hydrochloric acid at the
temperature of the body as 100, we have the digestive power of
hydrochloric acid at the temperature of 16° to 18° Cent. represented by
44.9; that of butyric acid at the same temperature being 15.6.”

We here see that at the lower of these two temperatures, hydrochloric
acid with pepsin digests, within the same time, rather less than half
the quantity of fibrin compared with what it digests at the higher
temperature; and the power of butyric acid is reduced in the same
proportion under similar conditions and temperatures. We have also seen
that butyric acid, which is much more efficacious than propionic or
valerianic acids, digests with pepsin at the higher temperature less
than a third of the fibrin which is digested at the same temperature by
hydrochloric acid.] [page 92]

I will now give in detail my experiments on the digestive power of the
secretion of Drosera, dividing the substances tried into two series,
namely those which are digested more or less completely, and those
which are not digested. We shall presently see that all these
substances are acted on by the gastric juice of the higher animals in
the same manner. I beg leave to call attention to the experiments under
the head albumen, showing that the secretion loses its power when
neutralised by an alkali, and recovers it when an acid is added.

Substances which are completely or partially digested by the Secretion
of Drosera.

Albumen.—After having tried various substances, Dr. Burdon Sanderson
suggested to me the use of cubes of coagulated albumen or hard-boiled
egg. I may premise that five cubes of the same size as those used in
the following experiments were placed for the sake of comparison at the
same time on wet moss close to the plants of Drosera. The weather was
hot, and after four days some of the cubes were discoloured and mouldy,
with their angles a little rounded; but they were not surrounded by a
zone of transparent fluid as in the case of those undergoing digestion.
Other cubes retained their angles and white colour. After eight days
all were somewhat reduced in size, discoloured, with their angles much
rounded. Nevertheless in four out of the five specimens, the central
parts were still white and opaque. So that their state differed widely,
as we shall see, from that of the cubes subjected to the action of the
secretion.

[Experiment 1.

Rather large cubes of albumen were first tried; the tentacles were well
inflected in 24 hrs.; after an [page 93] additional day the angles of
the cubes were dissolved and rounded;* but the cubes were too large, so
that the leaves were injured, and after seven days one died and the
others were dying. Albumen which has been kept for four or five days,
and which, it may be presumed, has begun to decay slightly, seems to
act more quickly than freshly boiled eggs. As the latter were generally
used, I often moistened them with a little saliva, to make the
tentacles close more quickly.

Experiment 2.—A cube of 1/10 of an inch (i.e. with each side 1/10 of an
inch, or 2.54 mm. in length) was placed on a leaf, and after 50 hrs. it
was converted into a sphere about 3/40 of an inch (1.905 mm.) in
diameter, surrounded by perfectly transparent fluid. After ten days the
leaf re-expanded, but there was still left on the disc a minute bit of
albumen now rendered transparent. More albumen had been given to this
leaf than could be dissolved or digested.

Experiment 3.—Two cubes of albumen of 1/20 of an inch (1.27 mm.) were
placed on two leaves. After 46 hrs. every atom of one was dissolved,
and most of the liquefied matter was absorbed, the fluid which remained
being in this, as in all other cases, very acid and viscid. The other
cube was acted on at a rather slower rate.

Experiment 4.—Two cubes of albumen of the same size as the last were
placed on two leaves, and were converted in 50 hrs. into two large
drops of transparent fluid; but when these were removed from beneath
the inflected tentacles, and viewed by reflected light under the
microscope, fine streaks of white opaque matter could be seen in the
one, and traces of similar streaks in the other. The drops were
replaced on the leaves, which re-expanded after 10 days; and now
nothing was left except a very little transparent acid fluid.

Experiment 5.—This experiment was slightly varied, so that the albumen
might be more quickly exposed to the action of the secretion. Two
cubes, each of about 1/40 of an inch (.635 mm.), were placed on the
same leaf, and two similar cubes on another

* In all my numerous experiments on the digestion of cubes of albumen,
the angles and edges were invariably first rounded. Now, Schiff states
(‘Leçons phys. de la Digestion,’ vol. ii. 1867, page 149) that this is
characteristic of the digestion of albumen by the gastric juice of
animals. On the other hand, he remarks “les dissolutions, en chimie,
ont lieu sur toute la surface des corps en contact avec l’agent
dissolvant.” [page 94]


leaf. These were examined after 21 hrs. 30 m., and all four were found
rounded. After 46 hrs. the two cubes on the one leaf were completely
liquefied, the fluid being perfectly transparent; on the other leaf
some opaque white streaks could still be seen in the midst of the
fluid. After 72 hrs. these streaks disappeared, but there was still a
little viscid fluid left on the disc; whereas it was almost all
absorbed on the first leaf. Both leaves were now beginning to
re-expand.]

The best and almost sole test of the presence of some ferment analogous
to pepsin in the secretion appeared to be to neutralise the acid of the
secretion with an alkali, and to observe whether the process of
digestion ceased; and then to add a little acid and observe whether the
process recommenced. This was done, and, as we shall see, with success,
but it was necessary first to try two control experiments; namely,
whether the addition of minute drops of water of the same size as those
of the dissolved alkalies to be used would stop the process of
digestion; and, secondly, whether minute drops of weak hydrochloric
acid, of the same strength and size as those to be used, would injure
the leaves. The two following experiments were therefore tried:—

Experiment 6.—Small cubes of albumen were put on three leaves, and
minute drops of distilled water on the head of a pin were added two or
three times daily. These did not in the least delay the process; for,
after 48 hrs., the cubes were completely dissolved on all three leaves.
On the third day the leaves began to re-expand, and on the fourth day
all the fluid was absorbed.

Experiment 7.—Small cubes of albumen were put on two leaves, and minute
drops of hydrochloric acid, of the strength of one part to 437 of
water, were added two or three times. This did not in the least delay,
but seemed rather to hasten, the process of digestion; for every trace
of the albumen disappeared in 24 hrs. 30 m. After three days the leaves
partially re-expanded, and by this time almost all the viscid fluid on
their discs was absorbed. It is almost superfluous to state that [page
95] cubes of albumen of the same size as those above used, left for
seven days in a little hydrochloric acid of the above strength,
retained all their angles as perfect as ever.

Experiment 8.—Cubes of albumen (of 1/20 of an inch, or 2.54 mm.) were
placed on five leaves, and minute drops of a solution of one part of
carbonate of soda to 437 of water were added at intervals to three of
them, and drops of carbonate of potash of the same strength to the
other two. The drops were given on the head of a rather large pin, and
I ascertained that each was equal to about 1/10 of a minim (.0059 ml.),
so that each contained only 1/4800 of a grain (.0135 mg.) of the
alkali. This was not sufficient, for after 46 hrs. all five cubes were
dissolved.

Experiment 9.—The last experiment was repeated on four leaves, with
this difference, that drops of the same solution of carbonate of soda
were added rather oftener, as often as the secretion became acid, so
that it was much more effectually neutralised. And now after 24 hrs.
the angles of three of the cubes were not in the least rounded, those
of the fourth being so in a very slight degree. Drops of extremely weak
hydrochloric acid (viz. one part to 847 of water) were then added, just
enough to neutralise the alkali which was still present; and now
digestion immediately recommenced, so that after 23 hrs. 30 m. three of
the cubes were completely dissolved, whilst the fourth was converted
into a minute sphere, surrounded by transparent fluid; and this sphere
next day disappeared.

Experiment 10.—Stronger solutions of carbonate of soda and of potash
were next used, viz. one part to 109 of water; and as the same-sized
drops were given as before, each drop contained 1/1200 of a grain
(.0539 mg.) of either salt. Two cubes of albumen (each about 1/40 of an
inch, or .635 mm.) were placed on the same leaf, and two on another.
Each leaf received, as soon as the secretion became slightly acid (and
this occurred four times within 24 hrs.), drops either of the soda or
potash, and the acid was thus effectually neutralised. The experiment
now succeeded perfectly, for after 22 hrs. the angles of the cubes were
as sharp as they were at first, and we know from experiment 5 that such
small cubes would have been completely rounded within this time by the
secretion in its natural state. Some of the fluid was now removed with
blotting-paper from the discs of the leaves, and minute drops of
hydrochloric acid of the strength of the one part to 200 of water was
added. Acid of this greater strength was used as the solutions of the
alkalies were stronger. The [page 96] process of digestion now
commenced, so that within 48 hrs. from the time when the acid was given
the four cubes were not only completely dissolved, but much of the
liquefied albumen was absorbed.

Experiment 11.—Two cubes of albumen (1/40 of an inch, or .635 mm.) were
placed on two leaves, and were treated with alkalies as in the last
experiment, and with the same result; for after 22 hrs. they had their
angles perfectly sharp, showing that the digestive process had been
completely arrested. I then wished to ascertain what would be the
effect of using stronger hydrochloric acid; so I added minute drops of
the strength of 1 per cent. This proved rather too strong, for after 48
hrs. from the time when the acid was added one cube was still almost
perfect, and the other only very slightly rounded, and both were
stained slightly pink. This latter fact shows that the leaves were
injured,* for during the normal process of digestion the albumen is not
thus coloured, and we can thus understand why the cubes were not
dissolved.]

From these experiments we clearly see that the secretion has the power
of dissolving albumen, and we further see that if an alkali is added,
the process of digestion is stopped, but immediately recommences as
soon as the alkali is neutralised by weak hydrochloric acid. Even if I
had tried no other experiments than these, they would have almost
sufficed to prove that the glands of Drosera secrete some ferment
analogous to pepsin, which in presence of an acid gives to the
secretion its power of dissolving albuminous compounds.

Splinters of clean glass were scattered on a large number of leaves,
and these became moderately inflected. They were cut off and divided
into three lots; two of them, after being left for some time in a
little distilled water, were strained, and some dis-

* Sachs remarks (‘Traité de Bot.’ 1874, p. 774), that cells which are
killed by freezing, by too great heat, or by chemical agents, allow all
their colouring matter to escape into the surrounding water. [page 97]


coloured, viscid, slightly acid fluid was thus obtained. The third lot
was well soaked in a few drops of glycerine, which is well known to
dissolve pepsin. Cubes of albumen (1/20 of an inch) were now placed in
the three fluids in watch-glasses, some of which were kept for several
days at about 90° Fahr. (32°.2 Cent.), and others at the temperature of
my room; but none of the cubes were dissolved, the angles remaining as
sharp as ever. This fact probably indicates that the ferment is not
secreted until the glands are excited by the absorption of a minute
quantity of already soluble animal matter,—a conclusion which is
supported by what we shall hereafter see with respect to Dionaea. Dr.
Hooker likewise found that, although the fluid within the pitchers of
Nepenthes possesses extraordinary power of digestion, yet when removed
from the pitchers before they have been excited and placed in a vessel,
it has no such power, although it is already acid; and we can account
for this fact only on the supposition that the proper ferment is not
secreted until some exciting matter is absorbed.

On three other occasions eight leaves were strongly excited with
albumen moistened with saliva; they were then cut off, and allowed to
soak for several hours or for a whole day in a few drops of glycerine.
Some of this extract was added to a little hydrochloric acid of various
strengths (generally one to 400 of water), and minute cubes of albumen
were placed in the mixture.* In two of these trials the cubes were not
in the least acted on; but in the third

* As a control experiment bits of albumen were placed in the same
glycerine with hydrochloric acid of the same strength; and the albumen,
as might have been expected, was not in the least affected after two
days. [page 98]


the experiment was successful. For in a vessel containing two cubes,
both were reduced in size in 3 hrs.; and after 24 hrs. mere streaks of
undissolved albumen were left. In a second vessel, containing two
minute ragged bits of albumen, both were likewise reduced in size in 3
hrs., and after 24 hrs. completely disappeared. I then added a little
weak hydrochloric acid to both vessels, and placed fresh cubes of
albumen in them; but these were not acted on. This latter fact is
intelligible according to the high authority of Schiff,* who has
demonstrated, as he believes, in opposition to the view held by some
physiologists, that a certain small amount of pepsin is destroyed
during the act of digestion. So that if my solution contained, as is
probable, an extremely small amount of the ferment, this would have
been consumed by the dissolution of the cubes of albumen first given;
none being left when the hydrochloric acid was added. The destruction
of the ferment during the process of digestion, or its absorption after
the albumen had been converted into a peptone, will also account for
only one out of the three latter sets of experiments having been
successful.

Digestion of Roast Meat.—Cubes of about 1/20 of an inch (1.27 mm.) of
moderately roasted meat were placed on five leaves which became in 12
hrs. closely inflected. After 48 hrs. I gently opened one leaf, and the
meat now consisted of a minute central sphere, partially digested and
surrounded by a thick envelope of transparent viscid fluid. The whole,
without being much disturbed, was removed and placed under the
microscope. In the central part the transverse striae on the muscular
fibres were quite distinct; and it was

* ‘Leçons phys. de la Digestion,’ 1867, tom. ii. pp. 114-126. [page 99]


interesting to observe how gradually they disappeared, when the same
fibre was traced into the surrounding fluid. They disappeared by the
striae being replaced by transverse lines formed of excessively minute
dark points, which towards the exterior could be seen only under a very
high power; and ultimately these points were lost. When I made these
observations, I had not read Schiff’s account* of the digestion of meat
by gastric juice, and I did not understand the meaning of the dark
points. But this is explained in the following statement, and we
further see how closely similar is the process of digestion by gastric
juice and by the secretion of Drosera.

“On a dit le suc gastrique faisait perdre à la fibre musculaire ses
stries transversales. Ainsi énoncée, cette proposition pourrait donner
lieu à une équivoque, car ce qui se perd, ce n’est que _l’aspect_
extérieur de la striature et non les éléments anatomiques qui la
composent. On sait que les stries qui donnent un aspect si
caractéristique à la fibre musculaire, sont le résultat de la
juxtaposition et du parallélisme des corpuscules élémentaires, placés,
à distances égales, dans l’intérieur des fibrilles contiguës. Or, dès
que le tissu connectif qui relie entre elles les fibrilles élémentaires
vient à se gonfler et à se dissoudre, et que les fibrilles elles-mêmes
se dissocient, ce parallélisme est détruit et avec lui l’aspect, le
phénomène optique des stries. Si, après la désagrégation des fibres, on
examine au microscope les fibrilles élémentaires, on distingue encore
très-nettement à leur intérieur les corpuscules, et on continue à les
voir, de plus en plus pâles, jusqu’au moment où les fibrilles
elles-mêmes se liquéfient et disparaissent dans le suc gastrique. Ce
qui constitue la striature, à proprement parler, n’est donc pas
détruit, avant la liquéfaction de la fibre charnue elle-même.”

In the viscid fluid surrounding the central sphere of undigested meat
there were globules of fat and little bits of fibro-elastic tissue;
neither of which were in

* ‘Leçons phys. de la Digestion,’ tom. ii. p. 145. [page 100]


the least digested. There were also little free parallelograms of
yellowish, highly translucent matter. Schiff, in speaking of the
digestion of meat by gastric juice, alludes to such parallelograms, and
says:—

“Le gonflement par lequel commence la digestion de la viande, résulte
de l’action du suc gastrique acide sur le tissu connectif qui se
dissout d’abord, et qui, par sa liquéfaction, désagrége les fibrilles.
Celles-ci se dissolvent ensuite en grande partie, mais, avant de passer
à l’état liquide, elles tendent à se briser en petits fragments
transversaux. Les ‘_sarcous elements_’ de Bowman, qui ne sont autre
chose que les produits de cette division transversale des fibrilles
élémentaires, peuvent être préparés et isolés à l’aide du suc
gastrique, pourvu qu’on n’attend pas jusqu’à la liquéfaction complète
du muscle.”

After an interval of 72 hrs., from the time when the five cubes were
placed on the leaves, I opened the four remaining ones. On two nothing
could be seen but little masses of transparent viscid fluid; but when
these were examined under a high power, fat-globules, bits of
fibro-elastic tissue, and some few parallelograms of sarcous matter,
could be distinguished, but not a vestige of transverse striae. On the
other two leaves there were minute spheres of only partially digested
meat in the centre of much transparent fluid.

Fibrin.—Bits of fibrin were left in water during four days, whilst the
following experiments were tried, but they were not in the least acted
on. The fibrin which I first used was not pure, and included dark
particles: it had either not been well prepared or had subsequently
undergone some change. Thin portions, about 1/10 of an inch square,
were placed on several leaves, and though the fibrin was soon
liquefied, the whole was never dissolved. Smaller particles were then
placed on four leaves, and minute [page 101] drops of hydrochloric acid
(one part to 437 of water) were added; this seemed to hasten the
process of digestion, for on one leaf all was liquified and absorbed
after 20 hrs.; but on the three other leaves some undissolved residue
was left after 48 hrs. It is remarkable that in all the above and
following experiments, as well as when much larger bits of fibrin were
used, the leaves were very little excited; and it was sometimes
necessary to add a little saliva to induce complete inflection. The
leaves, moreover, began to re-expand after only 48 hrs., whereas they
would have remained inflected for a much longer time had insects, meat,
cartilage, albumen, &c., been placed on them.

I then tried some pure white fibrin, sent me by Dr. Burdon Sanderson.

[Experiment 1.—Two particles, barely 1/20 of an inch (1.27 mm.) square,
were placed on opposite sides of the same leaf. One of these did not
excite the surrounding tentacles, and the gland on which it rested soon
dried. The other particle caused a few of the short adjoining tentacles
to be inflected, the more distant ones not being affected. After 24
hrs. both were almost, and after 72 hrs. completely, dissolved.

Experiment 2.—The same experiment with the same result, only one of the
two bits of fibrin exciting the short surrounding tentacles. This bit
was so slowly acted on that after a day I pushed it on to some fresh
glands. In three days from the time when it was first placed on the
leaf it was completely dissolved.

Experiment 3.—Bits of fibrin of about the same size as before were
placed on the discs of two leaves; these caused very little inflection
in 23 hrs., but after 48 hrs. both were well clasped by the surrounding
short tentacles, and after an additional 24 hrs. were completely
dissolved. On the disc of one of these leaves much clear acid fluid was
left.

Experiment 4.—Similar bits of fibrin were placed on the discs of two
leaves; as after 2 hrs. the glands seemed rather dry, they were freely
moistened with saliva; this soon caused strong inflection both of the
tentacles and blades, with copious [page 102] secretion from the
glands. In 18 hrs. the fibrin was completely liquefied, but undigested
atoms still floated in the liquid; these, however, disappeared in under
two additional days.]

From these experiments it is clear that the secretion completely
dissolves pure fibrin. The rate of dissolution is rather slow; but this
depends merely on this substance not exciting the leaves sufficiently,
so that only the immediately adjoining tentacles are inflected, and the
supply of secretion is small.

Syntonin.—This substance, extracted from muscle, was kindly prepared
for me by Dr. Moore. Very differently from fibrin, it acts quickly and
energetically. Small portions placed on the discs of three leaves
caused their tentacles and blades to be strongly inflected within 8
hrs.; but no further observations were made. It is probably due to the
presence of this substance that raw meat is too powerful a stimulant,
often injuring or even killing the leaves.

Areolar Tissue.—Small portions of this tissue from a sheep were placed
on the discs of three leaves; these became moderately well inflected in
24 hrs., but began to re-expand after 48 hrs., and were fully
re-expanded in 72 hrs., always reckoning from the time when the bits
were first given. This substance, therefore, like fibrin, excites the
leaves for only a short time. The residue left on the leaves, after
they were fully re-expanded, was examined under a high power and found
much altered, but, owing to the presence of a quantity of elastic
tissue, which is never acted on, could hardly be said to be in a
liquefied condition.

Some areolar tissue free from elastic tissue was next procured from the
visceral cavity of a toad, and moderately sized, as well as very small,
bits were placed on five leaves. After 24 hrs. two of the bits [page
103] were completely liquefied; two others were rendered transparent,
but not quite liquefied; whilst the fifth was but little affected.
Several glands on the three latter leaves were now moistened with a
little saliva, which soon caused much inflection and secretion, with
the result that in the course of 12 additional hrs. one leaf alone
showed a remnant of undigested tissue. On the discs of the four other
leaves (to one of which a rather large bit had been given) nothing was
left except some transparent viscid fluid. I may add that some of this
tissue included points of black pigment, and these were not at all
affected. As a control experiment, small portions of this tissue were
left in water and on wet moss for the same length of time, and remained
white and opaque. From these facts it is clear that areolar tissue is
easily and quickly digested by the secretion; but that it does not
greatly excite the leaves.

Cartilage.—Three cubes (1/20 of an inch or 1.27 mm.) of white,
translucent, extremely tough cartilage were cut from the end of a
slightly roasted leg-bone of a sheep. These were placed on three
leaves, borne by poor, small plants in my greenhouse during November;
and it seemed in the highest degree improbable that so hard a substance
would be digested under such unfavourable circumstances. Nevertheless,
after 48 hrs., the cubes were largely dissolved and converted into
minute spheres, surrounded by transparent, very acid fluid. Two of
these spheres were completely softened to their centres; whilst the
third still contained a very small irregularly shaped core of solid
cartilage. Their surfaces were seen under the microscope to be
curiously marked by prominent ridges, showing that the cartilage had
been unequally corroded by the secretion. I need hardly [page 104] say
that cubes of the same cartilage, kept in water for the same length of
time, were not in the least affected.

During a more favourable season, moderately sized bits of the skinned
ear of a cat, which includes cartilage, areolar and elastic tissue,
were placed on three leaves. Some of the glands were touched with
saliva, which caused prompt inflection. Two of the leaves began to
re-expand after three days, and the third on the fifth day. The fluid
residue left on their discs was now examined, and consisted in one case
of perfectly transparent, viscid matter; in the other two cases, it
contained some elastic tissue and apparently remnants of half digested
areolar tissue.

Fibro-cartilage (from between the vertebrae of the tail of a sheep).
Moderately sized and small bits (the latter about 1/20 of an inch) were
placed on nine leaves. Some of these were well and some very little
inflected. In the latter case the bits were dragged over the discs, so
that they were well bedaubed with the secretion, and many glands thus
irritated. All the leaves re-expanded after only two days; so that they
were but little excited by this substance. The bits were not liquefied,
but were certainly in an altered condition, being swollen, much more
transparent, and so tender as to disintegrate very easily. My son
Francis prepared some artificial gastric juice, which was proved
efficient by quickly dissolving fibrin, and suspended portions of the
fibro-cartilage in it. These swelled and became hyaline, exactly like
those exposed to the secretion of Drosera, but were not dissolved. This
result surprised me much, as two physiologists were of opinion that
fibro-cartilage would be easily digested by gastric juice. I therefore
asked Dr. Klein to examine the specimens; and [page 105] he reports
that the two which had been subjected to artificial gastric juice were
“in that state of digestion in which we find connective tissue when
treated with an acid, viz. swollen, more or less hyaline, the fibrillar
bundles having become homogeneous and lost their fibrillar structure.”
In the specimens which had been left on the leaves of Drosera, until
they re-expanded, “parts were altered, though only slightly so, in the
same manner as those subjected to the gastric juice as they had become
more transparent, almost hyaline, with the fibrillation of the bundles
indistinct.” Fibro-cartilage is therefore acted on in nearly the same
manner by gastric juice and by the secretion of Drosera.

Bone.—Small smooth bits of the dried hyoidal bone of a fowl moistened
with saliva were placed on two leaves, and a similarly moistened
splinter of an extremely hard, broiled mutton-chop bone on a third
leaf. These leaves soon became strongly inflected, and remained so for
an unusual length of time; namely, one leaf for ten and the other two
for nine days. The bits of bone were surrounded all the time by acid
secretion. When examined under a weak power, they were found quite
softened, so that they were readily penetrated by a blunt needle, torn
into fibres, or compressed. Dr. Klein was so kind as to make sections
of both bones and examine them. He informs me that both presented the
normal appearance of decalcified bone, with traces of the earthy salts
occasionally left. The corpuscles with their processes were very
distinct in most parts; but in some parts, especially near the
periphery of the hyoidal bone, none could be seen. Other parts again
appeared amorphous, with even the longitudinal striation of bone not
distinguishable. This amorphous structure, [page 106] as Dr. Klein
thinks, may be the result either of the incipient digestion of the
fibrous basis or of all the animal matter having been removed, the
corpuscles being thus rendered invisible. A hard, brittle, yellowish
substance occupied the position of the medulla in the fragments of the
hyoidal bone.

As the angles and little projections of the fibrous basis were not in
the least rounded or corroded, two of the bits were placed on fresh
leaves. These by the next morning were closely inflected, and remained
so,—the one for six and the other for seven days,—therefore for not so
long a time as on the first occasion, but for a much longer time than
ever occurs with leaves inflected over inorganic or even over many
organic bodies. The secretion during the whole time coloured litmus
paper of a bright red; but this may have been due to the presence of
the acid super-phosphate of lime. When the leaves re-expanded, the
angles and projections of the fibrous basis were as sharp as ever. I
therefore concluded, falsely as we shall presently see, that the
secretion cannot touch the fibrous basis of bone. The more probable
explanation is that the acid was all consumed in decomposing the
phosphate of lime which still remained; so that none was left in a free
state to act in conjunction with the ferment on the fibrous basis.

Enamel and Dentine.—As the secretion decalcified ordinary bone, I
determined to try whether it would act on enamel and dentine, but did
not expect that it would succeed with so hard a substance as enamel.
Dr. Klein gave me some thin transverse slices of the canine tooth of a
dog; small angular fragments of which were placed on four leaves; and
these were examined each succeeding day at the same hour. The results
are, I think, worth giving in detail.] [page 107]

[Experiment 1.—May 1st, fragment placed on leaf; 3rd, tentacles but
little inflected, so a little saliva was added; 6th, as the tentacles
were not strongly inflected, the fragment was transferred to another
leaf, which acted at first slowly, but by the 9th closely embraced it.
On the 11th this second leaf began to re-expand; the fragment was
manifestly softened, and Dr. Klein reports, “a great deal of enamel and
the greater part of the dentine decalcified.”

Experiment 2.—May 1st, fragment placed on leaf; 2nd, tentacles fairly
well inflected, with much secretion on the disc, and remained so until
the 7th, when the leaf re-expanded. The fragment was now transferred to
a fresh leaf, which next day (8th) was inflected in the strongest
manner, and thus remained until the 11th, when it re-expanded. Dr.
Klein reports, “a great deal of enamel and the greater part of the
dentine decalcified.”

Experiment 3.—May 1st, fragment moistened with saliva and placed on a
leaf, which remained well inflected until 5th, when it re-expanded. The
enamel was not at all, and the dentine only slightly, softened. The
fragment was now transferred to a fresh leaf, which next morning (6th)
was strongly inflected, and remained so until the 11th. The enamel and
dentine both now somewhat softened; and Dr. Klein reports, “less than
half the enamel, but the greater part of the dentine decalcified.”

Experiment 4.—May 1st, a minute and thin bit of dentine, moistened with
saliva, was placed on a leaf, which was soon inflected, and re-expanded
on the 5th. The dentine had become as flexible as thin paper. It was
then transferred to a fresh leaf, which next morning (6th) was strongly
inflected, and reopened on the 10th. The decalcified dentine was now so
tender that it was torn into shreds merely by the force of the
re-expanding tentacles.]

From these experiments it appears that enamel is attacked by the
secretion with more difficulty than dentine, as might have been
expected from its extreme hardness; and both with more difficulty than
ordinary bone. After the process of dissolution has once commenced, it
is carried on with greater ease; this may be inferred from the leaves,
to which the fragments were transferred, becoming in all four cases
strongly inflected in the course of a single day; whereas the first set
of leaves acted much less quickly and [page 108] energetically. The
angles or projections of the fibrous basis of the enamel and dentine
(except, perhaps, in No. 4, which could not be well observed) were not
in the least rounded; and Dr. Klein remarks that their microscopical
structure was not altered. But this could not have been expected, as
the decalcification was not complete in the three specimens which were
carefully examined.

Fibrous Basis of Bone.—I at first concluded, as already stated, that
the secretion could not digest this substance. I therefore asked Dr.
Burdon Sanderson to try bone, enamel, and dentine, in artificial
gastric juice, and he found that they were after a considerable time
completely dissolved. Dr. Klein examined some of the small lamellae,
into which part of the skull of a cat became broken up after about a
week’s immersion in the fluid, and he found that towards the edges the
“matrix appeared rarefied, thus producing the appearance as if the
canaliculi of the bone-corpuscles had become larger. Otherwise the
corpuscles and their canaliculi were very distinct.” So that with bone
subjected to artificial gastric juice complete decalcification precedes
the dissolution of the fibrous basis. Dr. Burdon Sanderson suggested to
me that the failure of Drosera to digest the fibrous basis of bone,
enamel, and dentine, might be due to the acid being consumed in the
decomposition of the earthy salts, so that there was none left for the
work of digestion. Accordingly, my son thoroughly decalcified the bone
of a sheep with weak hydrochloric acid; and seven minute fragments of
the fibrous basis were placed on so many leaves, four of the fragments
being first damped with saliva to aid prompt inflection. All seven
leaves became inflected, but only very moderately, in the course of a
day. [page 109] They quickly began to re-expand; five of them on the
second day, and the other two on the third day. On all seven leaves the
fibrous tissue was converted into perfectly transparent, viscid, more
or less liquefied little masses. In the middle, however, of one, my son
saw under a high power a few corpuscles, with traces of fibrillation in
the surrounding transparent matter. From these facts it is clear that
the leaves are very little excited by the fibrous basis of bone, but
that the secretion easily and quickly liquefies it, if thoroughly
decalcified. The glands which had remained in contact for two or three
days with the viscid masses were not discoloured, and apparently had
absorbed little of the liquefied tissue, or had been little affected by
it.

Phosphate of Lime.—As we have seen that the tentacles of the first set
of leaves remained clasped for nine or ten days over minute fragments
of bone, and the tentacles of the second set for six or seven days over
the same fragments, I was led to suppose that it was the phosphate of
lime, and not any included animal matter, which caused such long
continued inflection. It is at least certain from what has just been
shown that this cannot have been due to the presence of the fibrous
basis. With enamel and dentine (the former of which contains only 4 per
cent. of organic matter) the tentacles of two successive sets of leaves
remained inflected altogether for eleven days. In order to test my
belief in the potency of phosphate of lime, I procured some from Prof.
Frankland absolutely free of animal matter and of any acid. A small
quantity moistened with water was placed on the discs of two leaves.
One of these was only slightly affected; the other remained closely
inflected for ten days, when a few of the tentacles began to [page 110]
re-expand, the rest being much injured or killed. I repeated the
experiment, but moistened the phosphate with saliva to insure prompt
inflection; one leaf remained inflected for six days (the little saliva
used would not have acted for nearly so long a time) and then died; the
other leaf tried to re-expand on the sixth day, but after nine days
failed to do so, and likewise died. Although the quantity of phosphate
given to the above four leaves was extremely small, much was left in
every case undissolved. A larger quantity wetted with water was next
placed on the discs of three leaves; and these became most strongly
inflected in the course of 24 hrs. They never re-expanded; on the
fourth day they looked sickly, and on the sixth were almost dead. Large
drops of not very viscid fluid hung from their edges during the six
days. This fluid was tested each day with litmus paper, but never
coloured it; and this circumstance I do not understand, as the
superphosphate of lime is acid. I suppose that some superphosphate must
have been formed by the acid of the secretion acting on the phosphate,
but that it was all absorbed and injured the leaves; the large drops
which hung from their edges being an abnormal and dropsical secretion.
Anyhow, it is manifest that the phosphate of lime is a most powerful
stimulant. Even small doses are more or less poisonous, probably on the
same principle that raw meat and other nutritious substances, given in
excess, kill the leaves. Hence the conclusion, that the long continued
inflection of the tentacles over fragments of bone, enamel, and
dentine, is caused by the presence of phosphate of lime, and not of any
included animal matter, is no doubt correct.

Gelatine.—I used pure gelatine in thin sheets given [page 111] me by
Prof. Hoffmann. For comparison, squares of the same size as those
placed on the leaves were left close by on wet moss. These soon
swelled, but retained their angles for three days; after five days they
formed rounded, softened masses, but even on the eighth day a trace of
gelatine could still be detected. Other squares were immersed in water,
and these, though much swollen, retained their angles for six days.
Squares of 1/10 of an inch (2.54 mm.), just moistened with water, were
placed on two leaves; and after two or three days nothing was left on
them but some acid viscid fluid, which in this and other cases never
showed any tendency to regelatinise; so that the secretion must act on
the gelatine differently to what water does, and apparently in the same
manner as gastric juice.* Four squares of the same size as before were
then soaked for three days in water, and placed on large leaves; the
gelatine was liquefied and rendered acid in two days, but did not
excite much inflection. The leaves began to re-expand after four or
five days, much viscid fluid being left on their discs, as if but
little had been absorbed. One of these leaves, as soon as it
re-expanded, caught a small fly, and after 24 hrs. was closely
inflected, showing how much more potent than gelatine is the animal
matter absorbed from an insect. Some larger pieces of gelatine, soaked
for five days in water, were next placed on three leaves, but these did
not become much inflected until the third day; nor was the gelatine
completely liquefied until the fourth day. On this day one leaf began
to re-expand; the second on the fifth; and third on the sixth. These
several facts

* Dr. Lauder Brunton, ‘Handbook for the Phys. Laboratory,’ 1873, pp.
477, 487; Schiff, ‘Leçons phys. de la Digestion,’ 1867, p. 249. [page
112]


prove that gelatine is far from acting energetically on Drosera.

In the last chapter it was shown that a solution of isinglass of
commerce, as thick as milk or cream, induces strong inflection. I
therefore wished to compare its action with that of pure gelatine.
Solutions of one part of both substances to 218 of water were made; and
half-minim drops (.0296 ml.) were placed on the discs of eight leaves,
so that each received 1/480 of a grain, or .135 mg. The four with the
isinglass were much more strongly inflected than the other four. I
conclude therefore that isinglass contains some, though perhaps very
little, soluble albuminous matter. As soon as these eight leaves
re-expanded, they were given bits of roast meat, and in some hours all
became greatly inflected; again showing how much more meat excites
Drosera than does gelatine or isinglass. This is an interesting fact,
as it is well known that gelatine by itself has little power of
nourishing animals.*

Chondrin.—This was sent me by Dr. Moore in a gelatinous state. Some was
slowly dried, and a small chip was placed on a leaf, and a much larger
chip on a second leaf. The first was liquefied in a day; the larger
piece was much swollen and softened, but was not completely liquefied
until the third day. The undried jelly was next tried, and as a control
experiment small cubes were left in water for four days and retained
their angles. Cubes of the same size were placed on two leaves, and
larger cubes on two other leaves. The tentacles and laminae of the
latter were closely inflected after 22 hrs., but those of the

* Dr. Lauder Brunton gives in the ‘Medical Record,’ January 1873, p.
36, an account of Voit’s view of the indirect part which gelatine plays
in nutrition. [page 113]


two leaves with the smaller cubes only to a moderate degree. The jelly
on all four was by this time liquefied, and rendered very acid. The
glands were blackened from the aggregation of their protoplasmic
contents. In 46 hrs. from the time when the jelly was given, the leaves
had almost re-expanded, and completely so after 70 hrs.; and now only a
little slightly adhesive fluid was left unabsorbed on their discs.

One part of chondrin jelly was dissolved in 218 parts of boiling water,
and half-minim drops were given to four leaves; so that each received
about 1/480 of a grain (.135 mg.) of the jelly; and, of course, much
less of dry chondrin. This acted most powerfully, for after only 3 hrs.
30 m. all four leaves were strongly inflected. Three of them began to
re-expand after 24 hrs., and in 48 hrs. were completely open; but the
fourth had only partially re-expanded. All the liquefied chondrin was
by this time absorbed. Hence a solution of chondrin seems to act far
more quickly and energetically than pure gelatine or isinglass; but I
am assured by good authorities that it is most difficult, or
impossible, to know whether chondrin is pure, and if it contained any
albuminous compound, this would have produced the above effects.
Nevertheless, I have thought these facts worth giving, as there is so
much doubt on the nutritious value of gelatine; and Dr. Lauder Brunton
does not know of any experiments with respect to animals on the
relative value of gelatine and chondrin.

Milk.—We have seen in the last chapter that milk acts most powerfully
on the leaves; but whether this is due to the contained casein or
albumen, I know not. Rather large drops of milk excite so much
secretion (which is very acid) that it sometimes trickles down [page
114] from the leaves, and this is likewise characteristic of chemically
prepared casein. Minute drops of milk, placed on leaves, were
coagulated in about ten minutes. Schiff denies* that the coagulation of
milk by gastric juice is exclusively due to the acid which is present,
but attributes it in part to the pepsin; and it seems doubtful whether
with Drosera the coagulation can be wholly due to the acid, as the
secretion does not commonly colour litmus paper until the tentacles
have become well inflected; whereas the coagulation commences, as we
have seen, in about ten minutes. Minute drops of skimmed milk were
placed on the discs of five leaves; and a large proportion of the
coagulated matter or curd was dissolved in 6 hrs. and still more
completely in 8 hrs. These leaves re-expanded after two days, and the
viscid fluid left on their discs was then carefully scraped off and
examined. It seemed at first sight as if all the casein had not been
dissolved, for a little matter was left which appeared of a whitish
colour by reflected light. But this matter, when examined under a high
power, and when compared with a minute drop of skimmed milk coagulated
by acetic acid, was seen to consist exclusively of oil-globules, more
or less aggregated together, with no trace of casein. As I was not
familiar with the microscopical appearance of milk, I asked Dr. Lauder
Brunton to examine the slides, and he tested the globules with ether,
and found that they were dissolved. We may, therefore, conclude that
the secretion quickly dissolves casein, in the state in which it exists
in milk.

Chemically Prepared Casein.—This substance, which

* ‘Leçons,’ &c. tom. ii. page 151. [page 115]


is insoluble in water, is supposed by many chemists to differ from the
casein of fresh milk. I procured some, consisting of hard globules,
from Messrs. Hopkins and Williams, and tried many experiments with it.
Small particles and the powder, both in a dry state and moistened with
water, caused the leaves on which they were placed to be inflected very
slowly, generally not until two days had elapsed. Other particles,
wetted with weak hydrochloric acid (one part to 437 of water) acted in
a single day, as did some casein freshly prepared for me by Dr. Moore.
The tentacles commonly remained inflected for from seven to nine days;
and during the whole of this time the secretion was strongly acid. Even
on the eleventh day some secretion left on the disc of a fully
re-expanded leaf was strongly acid. The acid seems to be secreted
quickly, for in one case the secretion from the discal glands, on which
a little powdered casein had been strewed, coloured litmus paper,
before any of the exterior tentacles were inflected.

Small cubes of hard casein, moistened with water, were placed on two
leaves; after three days one cube had its angles a little rounded, and
after seven days both consisted of rounded softened masses, in the
midst of much viscid and acid secretion; but it must not be inferred
from this fact that the angles were dissolved, for cubes immersed in
water were similarly acted on. After nine days these leaves began to
re-expand, but in this and other cases the casein did not appear, as
far as could be judged by the eye, much, if at all, reduced in bulk.
According to Hoppe-Seyler and Lubavin* casein consists of an
albuminous, with

* Dr. Lauder Brunton, ‘Handbook for Phys. Lab.’ p. 529. [page 116]


a non-albuminous, substance; and the absorption of a very small
quantity of the former would excite the leaves, and yet not decrease
the casein to a perceptible degree. Schiff asserts*—and this is an
important fact for us—that “la casine purifie des chemistes est un
corps presque compltement inattaquable par le suc gastrique.” So that
here we have another point of accordance between the secretion of
Drosera and gastric juice, as both act so differently on the fresh
casein of milk, and on that prepared by chemists.

A few trials were made with cheese; cubes of 1/20 of an inch (1.27 mm.)
were placed on four leaves, and these after one or two days became well
inflected, their glands pouring forth much acid secretion. After five
days they began to re-expand, but one died, and some of the glands on
the other leaves were injured. Judging by the eye, the softened and
subsided masses of cheese, left on the discs, were very little or not
at all reduced in bulk. We may, however, infer from the time during
which the tentacles remained inflected,—from the changed colour of some
of the glands,—and from the injury done to others, that matter had been
absorbed from the cheese.

Legumin.—I did not procure this substance in a separate state; but
there can hardly be a doubt that it would be easily digested, judging
from the powerful effect produced by drops of a decoction of green
peas, as described in the last chapter. Thin slices of a dried pea,
after being soaked in water, were placed on two leaves; these became
somewhat inflected in the course of a single hour, and most strongly so
in 21 hrs. They re-expanded after three or four days.

* ‘Leçons’ &c. tom. ii. page 153. [page 117]


The slices were not liquefied, for the walls of the cells, composed of
cellulose, are not in the least acted on by the secretion.

Pollen.—A little fresh pollen from the common pea was placed on the
discs of five leaves, which soon became closely inflected, and remained
so for two or three days.

The grains being then removed, and examined under the microscope, were
found discoloured, with the oil-globules remarkably aggregated. Many
had their contents much shrunk, and some were almost empty. In only a
few cases were the pollen-tubes emitted. There could be no doubt that
the secretion had penetrated the outer coats of the grains, and had
partially digested their contents. So it must be with the gastric juice
of the insects which feed on pollen, without masticating it.* Drosera
in a state of nature cannot fail to profit to a certain extent by this
power of digesting pollen, as innumerable grains from the carices,
grasses, rumices, fir-trees, and other wind-fertilised plants, which
commonly grow in the same neighbourhood, will be inevitably caught by
the viscid secretion surrounding the many glands.

Gluten.—This substance is composed of two albuminoids, one soluble, the
other insoluble in alcohol.** Some was prepared by merely washing
wheaten flour in water. A provisional trial was made with rather large
pieces placed on two leaves; these, after 21 hrs., were closely
inflected, and remained so for four days, when one was killed and the
other had its glands extremely blackened, but was not afterwards
observed.

* Mr. A.W. Bennett found the undigested coats of the grains in the
intestinal canal of pollen-eating Diptera; see ‘Journal of Hort. Soc.
of London,’ vol. iv. 1874, p. 158.


** Watts’ ‘Dict. of Chemistry,’ vol. ii. 1872, p. 873. [page 118]


Smaller bits were placed on two leaves; these were only slightly
inflected in two days, but afterwards became much more so. Their
secretion was not so strongly acid as that of leaves excited by casein.
The bits of gluten, after lying for three days on the leaves, were more
transparent than other bits left for the same time in water. After
seven days both leaves re-expanded, but the gluten seemed hardly at all
reduced in bulk. The glands which had been in contact with it were
extremely black. Still smaller bits of half putrid gluten were now
tried on two leaves; these were well inflected in 24 hrs., and
thoroughly in four days, the glands in contact being much blackened.
After five days one leaf began to re-expand, and after eight days both
were fully re-expanded, some gluten being still left on their discs.
Four little chips of dried gluten, just dipped in water, were next
tried, and these acted rather differently from fresh gluten. One leaf
was almost fully re-expanded in three days, and the other three leaves
in four days. The chips were greatly softened, almost liquefied, but
not nearly all dissolved. The glands which had been in contact with
them, instead of being much blackened, were of a very pale colour, and
many of them were evidently killed.

In not one of these ten cases was the whole of the gluten dissolved,
even when very small bits were given. I therefore asked Dr. Burdon
Sanderson to try gluten in artificial digestive fluid of pepsin with
hydrochloric acid; and this dissolved the whole. The gluten, however,
was acted on much more slowly than fibrin; the proportion dissolved
within four hours being as 40.8 of gluten to 100 of fibrin. Gluten was
also tried in two other digestive fluids, in which hydrochloric acid
was replaced by propionic [page 119] and butyric acids, and it was
completely dissolved by these fluids at the ordinary temperature of a
room. Here, then, at last, we have a case in which it appears that
there exists an essential difference in digestive power between the
secretion of Drosera and gastric juice; the difference being confined
to the ferment, for, as we have just seen, pepsin in combination with
acids of the acetic series acts perfectly on gluten. I believe that the
explanation lies simply in the fact that gluten is too powerful a
stimulant (like raw meat, or phosphate of lime, or even too large a
piece of albumen), and that it injures or kills the glands before they
have had time to pour forth a sufficient supply of the proper
secretion. That some matter is absorbed from the gluten, we have clear
evidence in the length of time during which the tentacles remain
inflected, and in the greatly changed colour of the glands.

At the suggestion of Dr. Sanderson, some gluten was left for 15 hrs. in
weak hydrochloric acid (.02 per cent.), in order to remove the starch.
It became colourless, more transparent, and swollen. Small portions
were washed and placed on five leaves, which were soon closely
inflected, but to my surprise re-expanded completely in 48 hrs. A mere
vestige of gluten was left on two of the leaves, and not a vestige on
the other three. The viscid and acid secretion, which remained on the
discs of the three latter leaves, was scraped off and examined by my
son under a high power; but nothing could be seen except a little dirt,
and a good many starch grains which had not been dissolved by the
hydrochloric acid. Some of the glands were rather pale. We thus learn
that gluten, treated with weak hydrochloric acid, is not so powerful or
so enduring a [page 120] stimulant as fresh gluten, and does not much
injure the glands; and we further learn that it can be digested quickly
and completely by the secretion.

[Globulin or Crystallin.—This substance was kindly prepared for me from
the lens of the eye by Dr. Moore, and consisted of hard, colourless,
transparent fragments. It is said* that globulin ought to “swell up in
water and dissolve, for the most part forming a gummy liquid;” but this
did not occur with the above fragments, though kept in water for four
days. Particles, some moistened with water, others with weak
hydrochloric acid, others soaked in water for one or two days, were
placed on nineteen leaves. Most of these leaves, especially those with
the long soaked particles, became strongly inflected in a few hours.
The greater number re-expanded after three or four days; but three of
the leaves remained inflected during one, two, or three additional
days. Hence some exciting matter must have been absorbed; but the
fragments, though perhaps softened in a greater degree than those kept
for the same time in water, retained all their angles as sharp as ever.
As globulin is an albuminous substance, I was astonished at this
result; and my object being to compare the action of the secretion with
that of gastric juice, I asked Dr. Burdon Sanderson to try some of the
globulin used by me. He reports that “it was subjected to a liquid
containing 0.2 per cent. of hydrochloric acid, and about 1 per cent. of
glycerine extract of the stomach of a dog. It was then ascertained that
this liquid was capable of digesting 1.31 of its weight of unboiled
fibrin in 1 hr.; whereas, during the hour, only 0.141 of the above
globulin was dissolved. In both cases an excess of the substance to be
digested was subjected to the liquid.”** We thus see that within the
same time less than one-ninth by weight of globulin than of fibrin was
dissolved; and bearing in mind that pepsin with acids of the acetic
series has only about one-third of the digestive power of pepsin with
hydrochloric acid, it is not surprising that the fragments of

* Watts’ ‘Dictionary of Chemistry,’ vol. ii. page 874.


** I may add that Dr. Sanderson prepared some fresh globulin by
Schmidt’s method, and of this 0.865 was dissolved within the same time,
namely, one hour; so that it was far more soluble than that which I
used, though less soluble than fibrin, of which, as we have seen, 1.31
was dissolved. I wish that I had tried on Drosera globulin prepared by
this method. [page 121]


globulin were not corroded or rounded by the secretion of Drosera,
though some soluble matter was certainly extracted from them and
absorbed by the glands.

Haematin.—Some dark red granules, prepared from bullock’s blood, were
given me; these were found by Dr. Sanderson to be insoluble in water,
acids, and alcohol, so that they were probably haematin, together with
other bodies derived from the blood. Particles with little drops of
water were placed on four leaves, three of which were pretty closely
inflected in two days; the fourth only moderately so. On the third day
the glands in contact with the haematin were blackened, and some of the
tentacles seemed injured. After five days two leaves died, and the
third was dying; the fourth was beginning to re-expand, but many of its
glands were blackened and injured. It is therefore clear that matter
had been absorbed which was either actually poisonous or of too
stimulating a nature. The particles were much more softened than those
kept for the same time in water, but, judging by the eye, very little
reduced in bulk. Dr. Sanderson tried this substance with artificial
digestive fluid, in the manner described under globulin, and found that
whilst 1.31 of fibrin, only 0.456 of the haematin was dissolved in an
hour; but the dissolution by the secretion of even a less amount would
account for its action on Drosera. The residue left by the artificial
digestive fluid at first yielded nothing more to it during several
succeeding days.]

_Substances which are not Digested by the Secretion._


All the substances hitherto mentioned cause prolonged inflection of the
tentacles, and are either completely or at least partially dissolved by
the secretion. But there are many other substances, some of them
containing nitrogen, which are not in the least acted on by the
secretion, and do not induce inflection for a longer time than do
inorganic and insoluble objects. These unexciting and indigestible
substances are, as far as I have observed, epidermic productions (such
as bits of human nails, balls of hair, the quills of feathers),
fibro-elastic tissue, mucin, pepsin, urea, chitine, chlorophyll,
cellulose, gun-cotton, fat, oil, and starch. [page 122]

To these may be added dissolved sugar and gum, diluted alcohol, and
vegetable infusions not containing albumen, for none of these, as shown
in the last chapter, excite inflection. Now, it is a remarkable fact,
which affords additional and important evidence, that the ferment of
Drosera is closely similar to or identical with pepsin, that none of
these same substances are, as far as it is known, digested by the
gastric juice of animals, though some of them are acted on by the other
secretions of the alimentary canal. Nothing more need be said about
some of the above enumerated substances, excepting that they were
repeatedly tried on the leaves of Drosera, and were not in the least
affected by the secretion. About the others it will be advisable to
give my experiments.

[Fibro-elastic Tissue.—We have already seen that when little cubes of
meat, &c., were placed on leaves, the muscles, areolar tissue, and
cartilage were completely dissolved, but the fibro-elastic tissue, even
the most delicate threads, were left without the least signs of having
been attacked. And it is well known that this tissue cannot be digested
by the gastric juice of animals.*

Mucin.—As this substance contains about 7 per cent. of nitrogen, I
expected that it would have excited the leaves greatly and been
digested by the secretion, but in this I was mistaken. From what is
stated in chemical works, it appears extremely doubtful whether mucin
can be prepared as a pure principle. That which I used (prepared by Dr.
Moore) was dry and hard. Particles moistened with water were placed on
four leaves, but after two days there was only a trace of inflection in
the immediately adjoining tentacles. These leaves were then tried with
bits of meat, and all four soon became strongly inflected. Some of the
dried mucin was then soaked in water for two days, and little cubes of
the proper size were placed on three leaves. After four days the
tentacles

* See, for instance, Schiff, ‘Phys. de la Digestion,’ 1867, tom. ii.,
p. 38. [page 123]


round the margins of the discs were a little inflected, and the
secretion collected on the disc was acid, but the exterior tentacles
were not affected. One leaf began to re-expand on the fourth day, and
all were fully re-expanded on the sixth. The glands which had been in
contact with the mucin were a little darkened. We may therefore
conclude that a small amount of some impurity of a moderately exciting
nature had been absorbed. That the mucin employed by me did contain
some soluble matter was proved by Dr. Sanderson, who on subjecting it
to artificial gastric juice found that in 1 hr. some was dissolved, but
only in the proportion of 23 to 100 of fibrin during the same time. The
cubes, though perhaps rather softer than those left in water for the
same time, retained their angles as sharp as ever. We may therefore
infer that the mucin itself was not dissolved or digested. Nor is it
digested by the gastric juice of living animals, and according to
Schiff* it is a layer of this substance which protects the coats of the
stomach from being corroded during digestion.

Pepsin.—My experiments are hardly worth giving, as it is scarcely
possible to prepare pepsin free from other albuminoids; but I was
curious to ascertain, as far as that was possible, whether the ferment
of the secretion of Drosera would act on the ferment of the gastric
juice of animals. I first used the common pepsin sold for medicinal
purposes, and afterwards some which was much purer, prepared for me by
Dr. Moore. Five leaves to which a considerable quantity of the former
was given remained inflected for five days; four of them then died,
apparently from too great stimulation. I then tried Dr. Moore’s pepsin,
making it into a paste with water, and placing such small particles on
the discs of five leaves that all would have been quickly dissolved had
it been meat or albumen. The leaves were soon inflected; two of them
began to re-expand after only 20 hrs., and the other three were almost
completely re-expanded after 44 hrs. Some of the glands which had been
in contact with the particles of pepsin, or with the acid secretion
surrounding them, were singularly pale, whereas others were singularly
dark-coloured. Some of the secretion was scraped off and examined under
a high power; and it abounded with granules undistinguishable from
those of pepsin left in water for the same length of time. We may
therefore infer, as highly probable (remembering what small quantities
were given), that the ferment of Drosera does not act on or digest

* ‘Leçons phys. de la Digestion,’ 1867, tom. ii., p. 304. [page 124]


pepsin, but absorbs from it some albuminous impurity which induces
inflection, and which in large quantity is highly injurious. Dr. Lauder
Brunton at my request endeavoured to ascertain whether pepsin with
hydrochloric acid would digest pepsin, and as far as he could judge, it
had no such power. Gastric juice, therefore, apparently agrees in this
respect with the secretion of Drosera.

Urea.—It seemed to me an interesting inquiry whether this refuse of the
living body, which contains much nitrogen, would, like so many other
animal fluids and substances, be absorbed by the glands of Drosera and
cause inflection. Half-minim drops of a solution of one part to 437 of
water were placed on the discs of four leaves, each drop containing the
quantity usually employed by me, namely 1/960 of a grain, or .0674 mg.;
but the leaves were hardly at all affected. They were then tested with
bits of meat, and soon became closely inflected. I repeated the same
experiment on four leaves with some fresh urea prepared by Dr. Moore;
after two days there was no inflection; I then gave them another dose,
but still there was no inflection. These leaves were afterwards tested
with similarly sized drops of an infusion of raw meat, and in 6 hrs.
there was considerable inflection, which became excessive in 24 hrs.
But the urea apparently was not quite pure, for when four leaves were
immersed in 2 dr. (7.1 ml.) of the solution, so that all the glands,
instead of merely those on the disc, were enabled to absorb any small
amount of impurity in solution, there was considerable inflection after
24 hrs., certainly more than would have followed from a similar
immersion in pure water. That the urea, which was not perfectly white,
should have contained a sufficient quantity of albuminous matter, or of
some salt of ammonia, to have caused the above effect, is far from
surprising, for, as we shall see in the next chapter, astonishingly
small doses of ammonia are highly efficient. We may therefore conclude
that urea itself is not exciting or nutritious to Drosera; nor is it
modified by the secretion, so as to be rendered nutritious, for, had
this been the case, all the leaves with drops on their discs assuredly
would have been well inflected. Dr. Lauder Brunton informs me that from
experiments made at my request at St. Bartholomew’s Hospital it appears
that urea is not acted on by artificial gastric juice, that is by
pepsin with hydrochloric acid.

Chitine.—The chitinous coats of insects naturally captured by the
leaves do not appear in the least corroded. Small square pieces of the
delicate wing and of the elytron of a Staphylinus [page 125] were
placed on some leaves, and after these had re-expanded, the pieces were
carefully examined. Their angles were as sharp as ever, and they did
not differ in appearance from the other wing and elytron of the same
insect which had been left in water. The elytron, however, had
evidently yielded some nutritious matter, for the leaf remained clasped
over it for four days; whereas the leaves with bits of the true wing
re-expanded on the second day. Any one who will examine the excrement
of insect-eating animals will see how powerless their gastric juice is
on chitine.

Cellulose.—I did not obtain this substance in a separate state, but
tried angular bits of dry wood, cork, sphagnum moss, linen, and cotton
thread. None of these bodies were in the least attacked by the
secretion, and they caused only that moderate amount of inflection
which is common to all inorganic objects. Gun-cotton, which consists of
cellulose, with the hydrogen replaced by nitrogen, was tried with the
same result. We have seen that a decoction of cabbage-leaves excites
the most powerful inflection. I therefore placed two little square bits
of the blade of a cabbage-leaf, and four little cubes cut from the
midrib, on six leaves of Drosera. These became well inflected in 12
hrs., and remained so for between two and four days; the bits of
cabbage being bathed all the time by acid secretion. This shows that
some exciting matter, to which I shall presently refer, had been
absorbed; but the angles of the squares and cubes remained as sharp as
ever, proving that the framework of cellulose had not been attacked.
Small square bits of spinach-leaves were tried with the same result;
the glands pouring forth a moderate supply of acid secretion, and the
tentacles remaining inflected for three days. We have also seen that
the delicate coats of pollen grains are not dissolved by the secretion.
It is well known that the gastric juice of animals does not attack
cellulose.

Chlorophyll.—This substance was tried, as it contains nitrogen. Dr.
Moore sent me some preserved in alcohol; it was dried, but soon
deliquesced. Particles were placed on four leaves; after 3 hrs. the
secretion was acid; after 8 hrs. there was a good deal of inflection,
which in 24 hrs. became fairly well marked. After four days two of the
leaves began to open, and the other two were then almost fully
re-expanded. It is therefore clear that this chlorophyll contained
matter which excited the leaves to a moderate degree; but judging by
the eye, little or none was dissolved; so that in a pure state it would
not probably have been attacked by the secretion. Dr. Sanderson tried
that which I [page 126] used, as well as some freshly prepared, with
artificial digestive liquid, and found that it was not digested. Dr.
Lauder Brunton likewise tried some prepared by the process given in the
British Pharmacopoeia, and exposed it for five days at the temperature
of 37° Cent. to digestive liquid, but it was not diminished in bulk,
though the fluid acquired a slightly brown colour. It was also tried
with the glycerine extract of pancreas with a negative result. Nor does
chlorophyll seem affected by the intestinal secretions of various
animals, judging by the colour of their excrement.

It must not be supposed from these facts that the grains of
chlorophyll, as they exist in living plants, cannot be attacked by the
secretion; for these grains consist of protoplasm merely coloured by
chlorophyll. My son Francis placed a thin slice of spinach leaf,
moistened with saliva, on a leaf of Drosera, and other slices on damp
cotton-wool, all exposed to the same temperature. After 19 hrs. the
slice on the leaf of Drosera was bathed in much secretion from the
inflected tentacles, and was now examined under the microscope. No
perfect grains of chlorophyll could be distinguished; some were
shrunken, of a yellowish-green colour, and collected in the middle of
the cells; others were disintegrated and formed a yellowish mass,
likewise in the middle of the cells. On the other hand, in the slices
surrounded by damp cotton-wool, the grains of chlorophyll were green
and as perfect as ever. My son also placed some slices in artificial
gastric juice, and these were acted on in nearly the same manner as by
the secretion. We have seen that bits of fresh cabbage and spinach
leaves cause the tentacles to be inflected and the glands to pour forth
much acid secretion; and there can be little doubt that it is the
protoplasm forming the grains of chlorophyll, as well as that lining
the walls of the cells, which excites the leaves.

Fat and Oil.—Cubes of almost pure uncooked fat, placed on several
leaves, did not have their angles in the least rounded. We have also
seen that the oil-globules in milk are not digested. Nor does olive oil
dropped on the discs of leaves cause any inflection; but when they are
immersed in olive oil, they become strongly inflected; but to this
subject I shall have to recur. Oily substances are not digested by the
gastric juice of animals.

Starch.—Rather large bits of dry starch caused well-marked inflection,
and the leaves did not re-expand until the fourth day; but I have no
doubt that this was due to the prolonged irritation of the glands, as
the starch continued to absorb the secretion. The particles were not in
the least reduced in size; [page 127] and we know that leaves immersed
in an emulsion of starch are not at all affected. I need hardly say
that starch is not digested by the gastric juice of animals.

Action of the Secretion on Living Seeds.

The results of some experiments on living seeds, selected by hazard,
may here be given, though they bear only indirectly on our present
subject of digestion.

Seven cabbage seeds of the previous year were placed on the same number
of leaves. Some of these leaves were moderately, but the greater number
only slightly inflected, and most of them re-expanded on the third day.
One, however, remained clasped till the fourth, and another till the
fifth day. These leaves therefore were excited somewhat more by the
seeds than by inorganic objects of the same size. After they
re-expanded, the seeds were placed under favourable conditions on damp
sand; other seeds of the same lot being tried at the same time in the
same manner, and found to germinate well. Of the seven seeds which had
been exposed to the secretion, only three germinated; and one of the
three seedlings soon perished, the tip of its radicle being from the
first decayed, and the edges of its cotyledons of a dark brown colour;
so that altogether five out of the seven seeds ultimately perished.

Radish seeds (Raphanus sativus) of the previous year were placed on
three leaves, which became moderately inflected, and re-expanded on the
third or fourth day. Two of these seeds were transferred to damp sand;
only one germinated, and that very slowly. This seedling had an
extremely short, crooked, diseased, radicle, with no absorbent hairs;
and the cotyledons were oddly mottled with purple, with the edges
blackened and partly withered.

Cress seeds (Lepidum sativum) of the previous year were placed on four
leaves; two of these next morning were moderately and two strongly
inflected, and remained so for four, five, and even six days. Soon
after these seeds were placed on the leaves and had become damp, they
secreted in the usual manner a layer of tenacious mucus; and to
ascertain whether it was the absorption of this substance by the glands
which caused so much inflection, two seeds were put into water, and as
much of the mucus as possible scraped off. They were then placed on
leaves, which became very strongly inflected in the course of 3 hrs.,
and were still closely inflected on the third day; so that it evidently
was not the mucus which excited so [page 128] much inflection; on the
contrary, this served to a certain extent as a protection to the seeds.
Two of the six seeds germinated whilst still lying on the leaves, but
the seedlings, when transferred to damp sand, soon died; of the other
four seeds, only one germinated.

Two seeds of mustard (Sinapis nigra), two of celery (Apium
graveolens)—both of the previous year, two seeds well soaked of caraway
(Carum carui), and two of wheat, did not excite the leaves more than
inorganic objects often do. Five seeds, hardly ripe, of a buttercup
(Ranunculus), and two fresh seeds of Anemone nemorosa, induced only a
little more effect. On the other hand, four seeds, perhaps not quite
ripe, of Carex sylvatica caused the leaves on which they were placed to
be very strongly inflected; and these only began to re-expand on the
third day, one remaining inflected for seven days.

It follows from these few facts that different kinds of seeds excite
the leaves in very different degrees; whether this is solely due to the
nature of their coats is not clear. In the case of the cress seeds, the
partial removal of the layer of mucus hastened the inflection of the
tentacles. Whenever the leaves remain inflected during several days
over seeds, it is clear that they absorb some matter from them. That
the secretion penetrates their coats is also evident from the large
proportion of cabbage, raddish, and cress seeds which were killed, and
from several of the seedlings being greatly injured. This injury to the
seeds and seedlings may, however, be due solely to the acid of the
secretion, and not to any process of digestion; for Mr. Traherne
Moggridge has shown that very weak acids of the acetic series are
highly injurious to seeds. It never occurred to me to observe whether
seeds are often blown on to the viscid leaves of plants growing in a
state of nature; but this can hardly fail sometimes to occur, as we
shall hereafter see in the case of Pinguicula. If so, Drosera will
profit to a slight degree by absorbing matter from such seeds.]

A Summary and Concluding Remarks on the Digestive Power of Drosera.

When the glands on the disc are excited either by the absorption of
nitrogenous matter or by mechanical irritation, their secretion
increases in quantity and becomes acid. They likewise transmit [page
129] some influence to the glands of the exterior tentacles, causing
them to secrete more copiously; and their secretion likewise becomes
acid. With animals, according to Schiff,* mechanical irritation excites
the glands of the stomach to secrete an acid, but not pepsin. Now, I
have every reason to believe (though the fact is not fully
established), that although the glands of Drosera are continually
secreting viscid fluid to replace that lost by evaporation, yet they do
not secrete the ferment proper for digestion when mechanically
irritated, but only after absorbing certain matter, probably of a
nitrogenous nature. I infer that this is the case, as the secretion
from a large number of leaves which had been irritated by particles of
glass placed on their discs did not digest albumen; and more especially
from the analogy of Dionaea and Nepenthes. In like manner, the glands
of the stomach of animals secrete pepsin, as Schiff asserts, only after
they have absorbed certain soluble substances, which he designates as
peptogenes. There is, therefore, a remarkable parallelism between the
glands of Drosera and those of the stomach in the secretion of their
proper acid and ferment.

The secretion, as we have seen, completely dissolves albumen, muscle,
fibrin, areolar tissue, cartilage, the fibrous basis of bone, gelatine,
chondrin, casein in the state in which it exists in milk, and gluten
which has been subjected to weak hydrochloric acid. Syntonin and
legumin excite the leaves so powerfully and quickly that there can
hardly be a doubt that both would be dissolved by the secretion. The
secretion

* ‘Phys. de la Digestion,’ 1867, tom. ii. pp. 188, 245. [page 130]


failed to digest fresh gluten, apparently from its injuring the glands,
though some was absorbed. Raw meat, unless in very small bits, and
large pieces of albumen, &c., likewise injure the leaves, which seem to
suffer, like animals, from a surfeit. I know not whether the analogy is
a real one, but it is worth notice that a decoction of cabbage leaves
is far more exciting and probably nutritious to Drosera than an
infusion made with tepid water; and boiled cabbages are far more
nutritious, at least to man, than the uncooked leaves. The most
striking of all the cases, though not really more remarkable than many
others, is the digestion of so hard and tough a substance as cartilage.
The dissolution of pure phosphate of lime, of bone, dentine, and
especially enamel, seems wonderful; but it depends merely on the
long-continued secretion of an acid; and this is secreted for a longer
time under these circumstances than under any others. It was
interesting to observe that as long as the acid was consumed in
dissolving the phosphate of lime, no true digestion occurred; but that
as soon as the bone was completely decalcified, the fibrous basis was
attacked and liquefied with the greatest ease. The twelve substances
above enumerated, which are completely dissolved by the secretion, are
likewise dissolved by the gastric juice of the higher animals; and they
are acted on in the same manner, as shown by the rounding of the angles
of albumen, and more especially by the manner in which the transverse
striae of the fibres of muscle disappear.

The secretion of Drosera and gastric juice were both able to dissolve
some element or impurity out of the globulin and haematin employed by
me. The secretion also dissolved something out of chemically [page 131]
prepared casein, which is said to consist of two substances; and
although Schiff asserts that casein in this state is not attacked by
gastric juice, he might easily have overlooked a minute quantity of
some albuminous matter, which Drosera would detect and absorb. Again,
fibro-cartilage, though not properly dissolved, is acted on in the same
manner, both by the secretion of Drosera and gastric juice. But this
substance, as well as the so-called haematin used by me, ought perhaps
to have been classed with indigestible substances.

That gastric juice acts by means of its ferment, pepsin, solely in the
presence of an acid, is well established; and we have excellent
evidence that a ferment is present in the secretion of Drosera, which
likewise acts only in the presence of an acid; for we have seen that
when the secretion is neutralised by minute drops of the solution of an
alkali, the digestion of albumen is completely stopped, and that on the
addition of a minute dose of hydrochloric acid it immediately
recommences.

The nine following substances, or classes of substances, namely,
epidermic productions, fibro-elastic tissue, mucin, pepsin, urea,
chitine, cellulose, gun-cotton, chlorophyll, starch, fat and oil, are
not acted on by the secretion of Drosera; nor are they, as far as is
known, by the gastric juice of animals. Some soluble matter, however,
was extracted from the mucin, pepsin, and chlorophyll, used by me, both
by the secretion and by artificial gastric juice.

The several substances, which are completely dissolved by the
secretion, and which are afterwards absorbed by the glands, affect the
leaves rather differently. They induce inflection at very different
[page 132] rates and in very different degrees; and the tentacles
remain inflected for very different periods of time. Quick inflection
depends partly on the quantity of the substance given, so that many
glands are simultaneously affected, partly on the facility with which
it is penetrated and liquefied by the secretion, partly on its nature,
but chiefly on the presence of exciting matter already in solution.
Thus saliva, or a weak solution of raw meat, acts much more quickly
than even a strong solution of gelatine. So again leaves which have
re-expanded, after absorbing drops of a solution of pure gelatine or
isinglass (the latter being the more powerful of the two), if given
bits of meat, are inflected much more energetically and quickly than
they were before, notwithstanding that some rest is generally requisite
between two acts of inflection. We probably see the influence of
texture in gelatine and globulin when softened by having been soaked in
water acting more quickly than when merely wetted. It may be partly due
to changed texture, and partly to changed chemical nature, that
albumen, which had been kept for some time, and gluten which had been
subjected to weak hydrochloric acid, act more quickly than these
substances in their fresh state.

The length of time during which the tentacles remain inflected largely
depends on the quantity of the substance given, partly on the facility
with which it is penetrated or acted on by the secretion, and partly on
its essential nature. The tentacles always remain inflected much longer
over large bits or large drops than over small bits or drops. Texture
probably plays a part in determining the extraordinary length of time
during which the tentacles remain inflected [page 133] over the hard
grains of chemically prepared casein. But the tentacles remain
inflected for an equally long time over finely powdered, precipitated
phosphate of lime; phosphorus in this latter case evidently being the
attraction, and animal matter in the case of casein. The leaves remain
long inflected over insects, but it is doubtful how far this is due to
the protection afforded by their chitinous integuments; for animal
matter is soon extracted from insects (probably by exosmose from their
bodies into the dense surrounding secretion), as shown by the prompt
inflection of the leaves. We see the influence of the nature of
different substances in bits of meat, albumen, and fresh gluten acting
very differently from equal-sized bits of gelatine, areolar tissue, and
the fibrous basis of bone. The former cause not only far more prompt
and energetic, but more prolonged, inflection than do the latter. Hence
we are, I think, justified in believing that gelatine, areolar tissue,
and the fibrous basis of bone, would be far less nutritious to Drosera
than such substances as insects, meat, albumen, &c. This is an
interesting conclusion, as it is known that gelatine affords but little
nutriment to animals; and so, probably, would areolar tissue and the
fibrous basis of bone. The chondrin which I used acted more powerfully
than gelatine, but then I do not know that it was pure. It is a more
remarkable fact that fibrin, which belongs to the great class of
Proteids,* including albumen in one of its sub-groups, does not excite
the tentacles in a greater degree, or keep them inflected for a longer
time, than does gelatine, or

* See the classification adopted by Dr. Michael Foster in Watts’
‘Dictionary of Chemistry,’ Supplement 1872, page 969. [page 134]


areolar tissue, or the fibrous basis of bone. It is not known how long
an animal would survive if fed on fibrin alone, but Dr. Sanderson has
no doubt longer than on gelatine, and it would be hardly rash to
predict, judging from the effects on Drosera, that albumen would be
found more nutritious than fibrin. Globulin likewise belongs to the
Proteids, forming another sub-group, and this substance, though
containing some matter which excited Drosera rather strongly, was
hardly attacked by the secretion, and was very little or very slowly
attacked by gastric juice. How far globulin would be nutritious to
animals is not known. We thus see how differently the above specified
several digestible substances act on Drosera; and we may infer, as
highly probable, that they would in like manner be nutritious in very
different degrees both to Drosera and to animals.

The glands of Drosera absorb matter from living seeds, which are
injured or killed by the secretion. They likewise absorb matter from
pollen, and from fresh leaves; and this is notoriously the case with
the stomachs of vegetable-feeding animals. Drosera is properly an
insectivorous plant; but as pollen cannot fail to be often blown on to
the glands, as will occasionally the seeds and leaves of surrounding
plants, Drosera is, to a certain extent, a vegetable-feeder.

Finally, the experiments recorded in this chapter show us that there is
a remarkable accordance in the power of digestion between the gastric
juice of animals with its pepsin and hydrochloric acid and the
secretion of Drosera with its ferment and acid belonging to the acetic
series. We can, therefore, hardly doubt that the ferment in both cases
is closely similar, [page 135] if not identically the same. That a
plant and an animal should pour forth the same, or nearly the same,
complex secretion, adapted for the same purpose of digestion, is a new
and wonderful fact in physiology. But I shall have to recur to this
subject in the fifteenth chapter, in my concluding remarks on the
Droseraceae. [page 136]




CHAPTER VII.
THE EFFECTS OF SALTS OF AMMONIA.


Manner of performing the experiments—Action of distilled water in
comparison with the solutions—Carbonate of ammonia, absorbed by the
roots—The vapour absorbed by the glands—Drops on the disc—Minute drops
applied to separate glands—Leaves immersed in weak solutions—Minuteness
of the doses which induce aggregation of the protoplasm—Nitrate of
ammonia, analogous experiments with—Phosphate of ammonia, analogous
experiments with—Other salts of ammonia—Summary and concluding remarks
on the action of salts of ammonia.


The chief object in this chapter is to show how powerfully the salts of
ammonia act on the leaves of Drosera, and more especially to show what
an extraordinarily small quantity suffices to excite inflection. I
shall, therefore, be compelled to enter into full details. Doubly
distilled water was always used; and for the more delicate experiments,
water which had been prepared with the utmost possible care was given
me by Professor Frankland. The graduated measures were tested, and
found as accurate as such measures can be. The salts were carefully
weighed, and in all the more delicate experiments, by Borda’s double
method. But extreme accuracy would have been superfluous, as the leaves
differ greatly in irritability, according to age, condition, and
constitution. Even the tentacles on the same leaf differ in
irritability to a marked degree. My experiments were tried in the
following several ways.

[Firstly.—Drops which were ascertained by repeated trials to be on an
average about half a minim, or the 1/960 of a fluid ounce (.0296 ml.),
were placed by the same pointed instrument on the [page 137] discs of
the leaves, and the inflection of the exterior rows of tentacles
observed at successive intervals of time. It was first ascertained,
from between thirty and forty trials, that distilled water dropped in
this manner produces no effect, except that sometimes, though rarely,
two or three tentacles become inflected. In fact all the many trials
with solutions which were so weak as to produce no effect lead to the
same result that water is inefficient.

Secondly.—The head of a small pin, fixed into a handle, was dipped into
the solution under trial. The small drop which adhered to it, and which
was much too small to fall off, was cautiously placed, by the aid of a
lens, in contact with the secretion surrounding the glands of one, two,
three, or four of the exterior tentacles of the same leaf. Great care
was taken that the glands themselves should not be touched. I had
supposed that the drops were of nearly the same size; but on trial this
proved a great mistake. I first measured some water, and removed 300
drops, touching the pin’s head each time on blotting-paper; and on
again measuring the water, a drop was found to equal on an average
about the 1/60 of a minim. Some water in a small vessel was weighed
(and this is a more accurate method), and 300 drops removed as before;
and on again weighing the water, a drop was found to equal on an
average only the 1/89 of a minim. I repeated the operation, but
endeavoured this time, by taking the pin’s head out of the water
obliquely and rather quickly, to remove as large drops as possible; and
the result showed that I had succeeded, for each drop on an average
equalled 1/19.4 of a minim. I repeated the operation in exactly the
same manner, and now the drops averaged 1/23.5 of a minim. Bearing in
mind that on these two latter occasions special pains were taken to
remove as large drops as possible, we may safely conclude that the
drops used in my experiments were at least equal to the 1/20 of a
minim, or .0029 ml. One of these drops could be applied to three or
even four glands, and if the tentacles became inflected, some of the
solution must have been absorbed by all; for drops of pure water,
applied in the same manner, never produced any effect. I was able to
hold the drop in steady contact with the secretion only for ten to
fifteen seconds; and this was not time enough for the diffusion of all
the salt in solution, as was evident, from three or four tentacles
treated successively with the same drop, often becoming inflected. All
the matter in solution was even then probably not exhausted.

Thirdly.—Leaves cut off and immersed in a measured [page 138] quantity
of the solution under trial; the same number of leaves being immersed
at the same time, in the same quantity of the distilled water which had
been used in making the solution. The leaves in the two lots were
compared at short intervals of time, up to 24 hrs., and sometimes to 48
hrs. They were immersed by being laid as gently as possible in numbered
watch-glasses, and thirty minims (1.775 ml.) of the solution or of
water was poured over each.

Some solutions, for instance that of carbonate of ammonia, quickly
discolour the glands; and as all on the same leaf were discoloured
simultaneously, they must all have absorbed some of the salt within the
same short period of time. This was likewise shown by the simultaneous
inflection of the several exterior rows of tentacles. If we had no such
evidence as this, it might have been supposed that only the glands of
the exterior and inflected tentacles had absorbed the salt; or that
only those on the disc had absorbed it, and had then transmitted a
motor impulse to the exterior tentacles; but in this latter case the
exterior tentacles would not have become inflected until some time had
elapsed, instead of within half an hour, or even within a few minutes,
as usually occurred. All the glands on the same leaf are of nearly the
same size, as may best be seen by cutting off a narrow transverse
strip, and laying it on its side; hence their absorbing surfaces are
nearly equal. The long-headed glands on the extreme margin must be
excepted, as they are much longer than the others; but only the upper
surface is capable of absorption. Besides the glands, both surfaces of
the leaves and the pedicels of the tentacles bear numerous minute
papillae, which absorb carbonate of ammonia, an infusion of raw meat,
metallic salts, and probably many other substances, but the absorption
of matter by these papillae never induces inflection. We must remember
that the movement of each separate tentacle depends on its gland being
excited, except when a motor impulse is transmitted from the glands of
the disc, and then the movement, as just stated, does not take place
until some little time has elapsed. I have made these remarks because
they show us that when a leaf is immersed in a solution, and the
tentacles are inflected, we can judge with some accuracy how much of
the salt each gland has absorbed. For instance, if a leaf bearing 212
glands be immersed in a measured quantity of a solution, containing
1/10 of a grain of a salt, and all the exterior tentacles, except
twelve, are inflected, we may feel sure that each of the 200 glands can
on an average have absorbed at most 1/2000 of a grain of the salt. I
say at [page 139] most, for the papillae will have absorbed some small
amount, and so will perhaps the glands of the twelve excluded tentacles
which did not become inflected. The application of this principle leads
to remarkable conclusions with respect to the minuteness of the doses
causing inflection.

_On the Action of Distilled Water in Causing Inflection._


Although in all the more important experiments the difference between
the leaves simultaneously immersed in water and in the several
solutions will be described, nevertheless it may be well here to give a
summary of the effects of water. The fact, moreover, of pure water
acting on the glands deserves in itself some notice. Leaves to the
number of 141 were immersed in water at the same time with those in the
solutions, and their state recorded at short intervals of time.
Thirty-two other leaves were separately observed in water, making
altogether 173 experiments. Many scores of leaves were also immersed in
water at other times, but no exact record of the effects produced was
kept; yet these cursory observations support the conclusions arrived at
in this chapter. A few of the long-headed tentacles, namely from one to
about six, were commonly inflected within half an hour after immersion;
as were occasionally a few, and rarely a considerable number of the
exterior round-headed tentacles. After an immersion of from 5 to 8 hrs.
the short tentacles surrounding the outer parts of the disc generally
become inflected, so that their glands form a small dark ring on the
disc; the exterior tentacles not partaking of this movement. Hence,
excepting in a few cases hereafter to be specified, we can judge
whether a solution produces any effect only by observing the exterior
tentacles within the first 3 or 4 hrs. after immersion.

Now for a summary of the state of the 173 leaves after an immersion of
3 or 4 hrs. in pure water. One leaf had almost all its tentacles
inflected; three leaves had most of them sub-inflected; and thirteen
had on an average 36.5 tentacles inflected. Thus seventeen leaves out
of the 173 were acted on in a marked manner. Eighteen leaves had from
seven to nineteen tentacles inflected, the average being 9.3 tentacles
for each leaf. Forty-four leaves had from one to six tentacles
inflected, generally the long-headed ones. So that altogether of the
173 leaves carefully observed, seventy-nine were affected by the water
in some degree, though commonly to a very slight degree; and
ninety-four were not affected in the least degree. This [page 140]
amount of inflection is utterly insignificant, as we shall hereafter
see, compared with that caused by very weak solutions of several salts
of ammonia.

Plants which have lived for some time in a rather high temperature are
far more sensitive to the action of water than those grown out of
doors, or recently brought into a warm greenhouse. Thus in the above
seventeen cases, in which the immersed leaves had a considerable number
of tentacles inflected, the plants had been kept during the winter in a
very warm greenhouse; and they bore in the early spring remarkably fine
leaves, of a light red colour. Had I then known that the sensitiveness
of plants was thus increased, perhaps I should not have used the leaves
for my experiments with the very weak solutions of phosphate of
ammonia; but my experiments are not thus vitiated, as I invariably used
leaves from the same plants for simultaneous immersion in water. It
often happened that some leaves on the same plant, and some tentacles
on the same leaf, were more sensitive than others; but why this should
be so, I do not know.

FIG. 9. (Drosera rotundifolia.) Leaf (enlarged) with all the tentacles
closely inflected, from immersion in a solution of phosphate of ammonia
(one part to 87,500 of water.)

Besides the differences just indicated between the leaves immersed in
water and in weak solutions of ammonia, the tentacles of the latter are
in most cases much more closely inflected. The appearance of a leaf
after immersion in a few drops of a solution of 1 grain of phosphate of
ammonia to 200 oz. of water (i.e. one part to 87,500) is here
reproduced: such energetic inflection is never caused by water alone.
With leaves in the weak solutions, the blade or lamina often becomes
inflected; and this is so rare a circumstance with leaves in water that
I have seen only two instances; and in both of these the inflection was
very feeble. Again, with leaves in the weak solutions, the inflection
of the tentacles and blade often goes on steadily, though slowly,
increasing during many hours; and [page 141] this again is so rare a
circumstance with leaves in water that I have seen only three instances
of any such increase after the first 8 to 12 hrs.; and in these three
instances the two outer rows of tentacles were not at all affected.
Hence there is sometimes a much greater difference between the leaves
in water and in the weak solutions, after from 8 hrs. to 24 hrs., than
there was within the first 3 hrs.; though as a general rule it is best
to trust to the difference observed within the shorter time.

With respect to the period of the re-expansion of the leaves, when left
immersed either in water or in the weak solutions, nothing could be
more variable. In both cases the exterior tentacles not rarely begin to
re-expand, after an interval of only from 6 to 8 hrs.; that is just
about the time when the short tentacles round the borders of the disc
become inflected. On the other hand, the tentacles sometimes remain
inflected for a whole day, or even two days; but as a general rule they
remain inflected for a longer period in very weak solutions than in
water. In solutions which are not extremely weak, they never re-expand
within nearly so short a period as six or eight hours. From these
statements it might be thought difficult to distinguish between the
effects of water and the weaker solutions; but in truth there is not
the slightest difficulty until excessively weak solutions are tried;
and then the distinction, as might be expected, becomes very doubtful,
and at last disappears. But as in all, except the simplest, cases the
state of the leaves simultaneously immersed for an equal length of time
in water and in the solutions will be described, the reader can judge
for himself.]

CARBONATE OF AMMONIA.


This salt, when absorbed by the roots, does not cause the tentacles to
be inflected. A plant was so placed in a solution of one part of the
carbonate to 146 of water that the young uninjured roots could be
observed. The terminal cells, which were of a pink colour, instantly
became colourless, and their limpid contents cloudy, like a mezzo-tinto
engraving, so that some degree of aggregation was almost instantly
caused; but no further change ensued, and the absorbent hairs were not
visibly affected. The tentacles [page 142] did not bend. Two other
plants were placed with their roots surrounded by damp moss, in half an
ounce (14.198 ml.) of a solution of one part of the carbonate to 218 of
water, and were observed for 24 hrs.; but not a single tentacle was
inflected. In order to produce this effect, the carbonate must be
absorbed by the glands.

The vapour produces a powerful effect on the glands, and induces
inflection. Three plants with their roots in bottles, so that the
surrounding air could not have become very humid, were placed under a
bell-glass (holding 122 fluid ounces), together with 4 grains of
carbonate of ammonia in a watch-glass. After an interval of 6 hrs. 15
m. the leaves appeared unaffected; but next morning, after 20 hrs., the
blackened glands were secreting copiously, and most of the tentacles
were strongly inflected. These plants soon died. Two other plants were
placed under the same bell-glass, together with half a grain of the
carbonate, the air being rendered as damp as possible; and in 2 hrs.
most of the leaves were affected, many of the glands being blackened
and the tentacles inflected. But it is a curious fact that some of the
closely adjoining tentacles on the same leaf, both on the disc and
round the margins, were much, and some, apparently, not in the least
affected. The plants were kept under the bell-glass for 24 hrs., but no
further change ensued. One healthy leaf was hardly at all affected,
though other leaves on the same plant were much affected. On some
leaves all the tentacles on one side, but not those on the opposite
side, were inflected. I doubt whether this extremely unequal action can
be explained by supposing that the more active glands absorb all the
vapour as quickly as it is generated, so that none is left for the
others, for we shall meet with [page 143] analogous cases with air
thoroughly permeated with the vapours of chloroform and ether.

Minute particles of the carbonate were added to the secretion
surrounding several glands. These instantly became black and secreted
copiously; but, except in two instances, when extremely minute
particles were given, there was no inflection. This result is analogous
to that which follows from the immersion of leaves in a strong solution
of one part of the carbonate to 109, or 146, or even 218 of water, for
the leaves are then paralysed and no inflection ensues, though the
glands are blackened, and the protoplasm in the cells of the tentacles
undergoes strong aggregation.

[We will now turn to the effects of solutions of the carbonate.
Half-minims of a solution of one part to 437 of water were placed on
the discs of twelve leaves; so that each received 1/960 of a grain or
.0675 mg. Ten of these had their tentacles well inflected; the blades
of some being also much curved inwards. In two cases several of the
exterior tentacles were inflected in 35 m.; but the movement was
generally slower. These ten leaves re-expanded in periods varying
between 21 hrs. and 45 hrs., but in one case not until 67 hrs. had
elapsed; so that they re-expanded much more quickly than leaves which
have caught insects.

The same-sized drops of a solution of one part to 875 of water were
placed on the discs of eleven leaves; six remained quite unaffected,
whilst five had from three to six or eight of their exterior tentacles
inflected; but this degree of movement can hardly be considered as
trustworthy. Each of these leaves received 1/1920 of a grain (.0337
mg.), distributed between the glands of the disc, but this was too
small an amount to produce any decided effect on the exterior
tentacles, the glands of which had not themselves received any of the
salt.

Minute drops on the head of a small pin, of a solution of one part of
the carbonate to 218 of water, were next tried in the manner above
described. A drop of this kind equals on an average 1/20 of a minim,
and therefore contains 1/4800 of a grain (.0135 mg.) of the carbonate.
I touched with it the viscid secretion round three glands, so that each
gland received only [page 144] 1/14400 of a grain (.00445 mg.).
Nevertheless, in two trials all the glands were plainly blackened; in
one case all three tentacles were well inflected after an interval of 2
hrs. 40 m.; and in another case two of the three tentacles were
inflected. I then tried drops of a weaker solution of one part to 292
of water on twenty-four glands, always touching the viscid secretion
round three glands with the same little drop. Each gland thus received
only the 1/19200 of a grain (.00337 mg.), yet some of them were a
little darkened; but in no one instance were any of the tentacles
inflected, though they were watched for 12 hrs. When a still weaker
solution (viz. one part to 437 of water) was tried on six glands, no
effect whatever was perceptible. We thus learn that the 1/14400 of a
grain (.00445 mg.) of carbonate of ammonia, if absorbed by a gland,
suffices to induce inflection in the basal part of the same tentacle;
but as already stated, I was able to hold with a steady hand the minute
drops in contact with the secretion only for a few seconds; and if more
time had been allowed for diffusion and absorption, a much weaker
solution would certainly have acted.

Some experiments were made by immersing cut-off leaves in solutions of
different strengths. Thus four leaves were left for about 3 hrs. each
in a drachm (3.549 ml.) of a solution of one part of the carbonate to
5250 of water; two of these had almost every tentacle inflected, the
third had about half the tentacles and the fourth about one-third
inflected; and all the glands were blackened. Another leaf was placed
in the same quantity of a solution of one part to 7000 of water, and in
1 hr. 16 m. every single tentacle was well inflected, and all the
glands blackened. Six leaves were immersed, each in thirty minims
(1.774 ml.) of a solution of one part to 4375 of water, and the glands
were all blackened in 31 m. All six leaves exhibited some slight
inflection, and one was strongly inflected. Four leaves were then
immersed in thirty minims of a solution of one part to 8750 of water,
so that each leaf received the 1/320 of a grain (.2025 mg.). Only one
became strongly inflected; but all the glands on all the leaves were of
so dark a red after one hour as almost to deserve to be called black,
whereas this did not occur with the leaves which were at the same time
immersed in water; nor did water produce this effect on any other
occasion in nearly so short a time as an hour. These cases of the
simultaneous darkening or blackening of the glands from the action of
weak solutions are important, as they show that all the glands absorbed
the carbonate within the same time, which fact indeed there was not the
least reason to doubt. So again, whenever all the [page 145] tentacles
become inflected within the same time, we have evidence, as before
remarked, of simultaneous absorption. I did not count the number of
glands on these four leaves; but as they were fine ones, and as we know
that the average number of glands on thirty-one leaves was 192, we may
safely assume that each bore on an average at least 170; and if so,
each blackened gland could have absorbed only 1/54400 of a grain
(.00119 mg.) of the carbonate.

A large number of trials had been previously made with solutions of one
part of the nitrate and phosphate of ammonia to 43750 of water (i.e.
one grain to 100 ounces), and these were found highly efficient.
Fourteen leaves were therefore placed, each in thirty minims of a
solution of one part of the carbonate to the above quantity of water;
so that each leaf received 1/1600 of a grain (.0405 mg.). The glands
were not much darkened. Ten of the leaves were not affected, or only
very slightly so. Four, however, were strongly affected; the first
having all the tentacles, except forty, inflected in 47 m.; in 6 hrs.
30 m. all except eight; and after 4 hrs. the blade itself. The second
leaf after 9 m. had all its tentacles except nine inflected; after 6
hrs. 30 m. these nine were sub-inflected; the blade having become much
inflected in 4 hrs. The third leaf after 1 hr. 6 m. had all but forty
tentacles inflected. The fourth, after 2 hrs. 5 m., had about half its
tentacles and after 4 hrs. all but forty-five inflected. Leaves which
were immersed in water at the same time were not at all affected, with
the exception of one; and this not until 8 hrs. had elapsed. Hence
there can be no doubt that a highly sensitive leaf, if immersed in a
solution, so that all the glands are enabled to absorb, is acted on by
1/1600 of a grain of the carbonate. Assuming that the leaf, which was a
large one, and which had all its tentacles excepting eight inflected,
bore 170 glands, each gland could have absorbed only 1/268800 of a
grain (.00024 mg.); yet this sufficed to act on each of the 162
tentacles which were inflected. But as only four out of the above
fourteen leaves were plainly affected, this is nearly the minimum dose
which is efficient.

Aggregation of the Protoplasm from the Action of Carbonate of
Ammonia.—I have fully described in the third chapter the remarkable
effects of moderately strong doses of this salt in causing the
aggregation of the protoplasm within the cells of the glands and
tentacles; and here my object is merely to show what small doses
suffice. A leaf was immersed in twenty minims (1.183 ml.) of a solution
of one part to 1750 of water, [page 146] and another leaf in the same
quantity of a solution of one part to 3062; in the former case
aggregation occurred in 4 m., in the latter in 11 m. A leaf was then
immersed in twenty minims of a solution of one part to 4375 of water,
so that it received 1/240 of a grain (.27 mg.); in 5 m. there was a
slight change of colour in the glands, and in 15 m. small spheres of
protoplasm were formed in the cells beneath the glands of all the
tentacles. In these cases there could not be a shadow of a doubt about
the action of the solution.

A solution was then made of one part to 5250 of water, and I
experimented on fourteen leaves, but will give only a few of the cases.
Eight young leaves were selected and examined with care, and they
showed no trace of aggregation. Four of these were placed in a drachm
(3.549 ml.) of distilled water; and four in a similar vessel, with a
drachm of the solution. After a time the leaves were examined under a
high power, being taken alternately from the solution and the water.
The first leaf was taken out of the solution after an immersion of 2
hrs. 40 m., and the last leaf out of the water after 3 hrs. 50 m.; the
examination lasting for 1 hr. 40 m. In the four leaves out of the water
there was no trace of aggregation except in one specimen, in which a
very few, extremely minute spheres of protoplasm were present beneath
some of the round glands. All the glands were translucent and red. The
four leaves which had been immersed in the solution, besides being
inflected, presented a widely different appearance; for the contents of
the cells of every single tentacle on all four leaves were
conspicuously aggregated; the spheres and elongated masses of
protoplasm in many cases extending halfway down the tentacles. All the
glands, both those of the central and exterior tentacles, were opaque
and blackened; and this shows that all had absorbed some of the
carbonate. These four leaves were of very nearly the same size, and the
glands were counted on one and found to be 167. This being the case,
and the four leaves having been immersed in a drachm of the solution,
each gland could have received on an average only 1/64128 of a grain
(.001009 mg.) of the salt; and this quantity sufficed to induce within
a short time conspicuous aggregation in the cells beneath all the
glands.

A vigorous but rather small red leaf was placed in six minims of the
same solution (viz. one part to 5250 of water), so that it received
1/960 of a grain (.0675 mg.). In 40 m. the glands appeared rather
darker; and in 1 hr. from four to six spheres of protoplasm were formed
in the cells beneath the glands of all the tentacles. I did not count
the tentacles, but we may [page 147] safely assume that there were at
least 140; and if so, each gland could have received only the 1/134400
of a grain, or .00048 mg.

A weaker solution was then made of one part to 7000 of water, and four
leaves were immersed in it; but I will give only one case. A leaf was
placed in ten minims of this solution; after 1 hr. 37 m. the glands
became somewhat darker, and the cells beneath all of them now contained
many spheres of aggregated protoplasm. This leaf received 1/768 of a
grain, and bore 166 glands. Each gland could, therefore, have received
only 1/127488 of a grain (.00507 mg.) of the carbonate.

Two other experiments are worth giving. A leaf was immersed for 4 hrs.
15 m. in distilled water, and there was no aggregation; it was then
placed for 1 hr. 15 m. in a little solution of one part to 5250 of
water; and this excited well-marked aggregation and inflection. Another
leaf, after having been immersed for 21 hrs. 15 m. in distilled water,
had its glands blackened, but there was no aggregation in the cells
beneath them; it was then left in six minims of the same solution, and
in 1 hr. there was much aggregation in many of the tentacles; in 2 hrs.
all the tentacles (146 in number) were affected—the aggregation
extending down for a length equal to half or the whole of the glands.
It is extremely improbable that these two leaves would have undergone
aggregation if they had been left for a little longer in the water,
namely for 1 hr. and 1 hr. 15 m., during which time they were immersed
in the solution; for the process of aggregation seems invariably to
supervene slowly and very gradually in water.]

A Summary of the Results with Carbonate of Ammonia.—The roots absorb
the solution, as shown by their changed colour, and by the aggregation
of the contents of their cells. The vapour is absorbed by the glands;
these are blackened, and the tentacles are inflected. The glands of the
disc, when excited by a half-minim drop (.0296 ml.), containing 1/960
of a grain (.0675 mg.), transmit a motor impulse to the exterior
tentacles, causing them to bend inwards. A minute drop, containing
1/14400 of a grain (.00445 mg.), if held for a few seconds in contact
with a gland, soon causes the tentacle bearing it to be inflected. If a
leaf is left [page 148] immersed for a few hours in a solution, and a
gland absorbs the 1/134400 of a grain (.0048 mg.), its colour becomes
darker, though not actually black; and the contents of the cells
beneath the gland are plainly aggregated. Lastly, under the same
circumstances, the absorption by a gland of the 1/268800 of a grain
(.00024 mg.) suffices to excite the tentacle bearing this gland into
movement.

NITRATE OF AMMONIA.


With the salt I attended only to the inflection of the leaves, for it
is far less efficient than the carbonate in causing aggregation,
although considerably more potent in causing inflection. I experimented
with half-minims (.0296 ml.) on the discs of fifty-two leaves, but will
give only a few cases. A solution of one part to 109 of water was too
strong, causing little inflection, and after 24 hrs. killing, or nearly
killing, four out of six leaves which were thus tried; each of which
received the 1/240 of a grain (or .27 mg.). A solution of one part to
218 of water acted most energetically, causing not only the tentacles
of all the leaves, but the blades of some, to be strongly inflected.
Fourteen leaves were tried with drops of a solution of one part to 875
of water, so that the disc of each received the 1/1920 of a grain
(.0337 mg.). Of these leaves, seven were very strongly acted on, the
edges being generally inflected; two were moderately acted on; and five
not at all. I subsequently tried three of these latter five leaves with
urine, saliva, and mucus, but they were only slightly affected; and
this proves that they were not in an active condition. I mention this
fact to show how necessary it is to experiment on several leaves. Two
of the leaves, which were well inflected, re-expanded after 51 hrs.

In the following experiment I happened to select very sensitive leaves.
Half-minims of a solution of one part to 1094 of water (i.e. 1 gr. to 2
1/2 oz.) were placed on the discs of nine leaves, so that each received
the 1/2400 of a grain (.027 mg.). Three of them had their tentacles
strongly inflected and their blades curled inwards; five were slightly
and somewhat doubtfully affected, having from three to eight of their
exterior tentacles inflected: one leaf was not at all affected, yet was
afterwards acted on by saliva. In six of these cases, a trace of action
was perceptible in [page 149] 7 hrs., but the full effect was not
produced until from 24 hrs. to 30 hrs. had elapsed. Two of the leaves,
which were only slightly inflected, re-expanded after an additional
interval of 19 hrs.

Half-minims of a rather weaker solution, viz. of one part to 1312 of
water (1 gr. to 3 oz.) were tried on fourteen leaves; so that each
received 1/2880 of a grain (.0225 mg.), instead of, as in the last
experiment, 1/2400 of a grain. The blade of one was plainly inflected,
as were six of the exterior tentacles; the blade of a second was
slightly, and two of the exterior tentacles well, inflected, all the
other tentacles being curled in at right angles to the disc; three
other leaves had from five to eight tentacles inflected; five others
only two or three, and occasionally, though very rarely, drops of pure
water cause this much action; the four remaining leaves were in no way
affected, yet three of them, when subsequently tried with urine, became
greatly inflected. In most of these cases a slight effect was
perceptible in from 6 hrs. to 7 hrs., but the full effect was not
produced until from 24 hrs. to 30 hrs. had elapsed. It is obvious that
we have here reached very nearly the minimum amount, which, distributed
between the glands of the disc, acts on the exterior tentacles; these
having themselves not received any of the solution.

In the next place, the viscid secretion round three of the exterior
glands was touched with the same little drop (1/20 of a minim) of a
solution of one part to 437 of water; and after an interval of 2 hrs.
50 m. all three tentacles were well inflected. Each of these glands
could have received only the 1/28800 of a grain, or .00225 mg. A little
drop of the same size and strength was also applied to four other
glands, and in 1 hr. two became inflected, whilst the other two never
moved. We here see, as in the case of the half-minims placed on the
discs, that the nitrate of ammonia is more potent in causing inflection
than the carbonate; for minute drops of the latter salt of this
strength produced no effect. I tried minute drops of a still weaker
solution of the nitrate, viz. one part to 875 of water, on twenty-one
glands, but no effect whatever was produced, except perhaps in one
instance.

Sixty-three leaves were immersed in solutions of various strengths;
other leaves being immersed at the same time in the same pure water
used in making the solutions. The results are so remarkable, though
less so than with phosphate of ammonia, that I must describe the
experiments in detail, but I will give only a few. In speaking of the
successive periods when inflection occurred, I always reckon from the
time of first immersion. [page 150]

Having made some preliminary trials as a guide, five leaves were placed
in the same little vessel in thirty minims of a solution of one part of
the nitrate to 7875 of water (1 gr. to 18 oz.); and this amount of
fluid just sufficed to cover them. After 2 hrs. 10 m. three of the
leaves were considerably inflected, and the other two moderately. The
glands of all became of so dark a red as almost to deserve to be called
black. After 8 hrs. four of the leaves had all their tentacles more or
less inflected; whilst the fifth, which I then perceived to be an old
leaf, had only thirty tentacles inflected. Next morning, after 23 hrs.
40 m., all the leaves were in the same state, excepting that the old
leaf had a few more tentacles inflected. Five leaves which had been
placed at the same time in water were observed at the same intervals of
time; after 2 hrs. 10 m. two of them had four, one had seven, one had
ten, of the long-headed marginal tentacles, and the fifth had four
round-headed tentacles, inflected. After 8 hrs. there was no change in
these leaves, and after 24 hrs. all the marginal tentacles had
re-expanded; but in one leaf, a dozen, and in a second leaf, half a
dozen, submarginal tentacles had become inflected. As the glands of the
five leaves in the solution were simultaneously darkened, no doubt they
had all absorbed a nearly equal amount of the salt: and as 1/288 of a
grain was given to the five leaves together, each got 1/1440 of a grain
(.045 mg.). I did not count the tentacles on these leaves, which were
moderately fine ones, but as the average number on thirty-one leaves
was 192, it would be safe to assume that each bore on an average at
least 160. If so, each of the darkened glands could have received only
1/230400 of a grain of the nitrate; and this caused the inflection of a
great majority of the tentacles.

This plan of immersing several leaves in the same vessel is a bad one,
as it is impossible to feel sure that the more vigorous leaves do not
rob the weaker ones of their share of the salt. The glands, moreover,
must often touch one another or the sides of the vessel, and movement
may have been thus excited; but the corresponding leaves in water,
which were little inflected, though rather more so than commonly
occurs, were exposed in an almost equal degree to these same sources of
error. I will, therefore, give only one other experiment made in this
manner, though many were tried and all confirmed the foregoing and
following results. Four leaves were placed in forty minims of a
solution of one part to 10,500 of water; and assuming that they
absorbed equally, each leaf received 1/1152 of a grain (.0562 mg.).
After 1 hr. 20 m. many of the tentacles on all four leaves were
somewhat inflected. After [page 151] 5 hrs. 30 m. two leaves had all
their tentacles inflected; a third leaf all except the extreme
marginals, which seemed old and torpid; and the fourth a large number.
After 21 hrs. every single tentacle, on all four leaves, was closely
inflected. Of the four leaves placed at the same time in water, one
had, after 5 hrs. 45 m., five marginal tentacles inflected; a second,
ten; a third, nine marginals and submarginals; and the fourth, twelve,
chiefly submarginals, inflected. After 21 hrs. all these marginal
tentacles re-expanded, but a few of the submarginals on two of the
leaves remained slightly curved inwards. The contrast was wonderfully
great between these four leaves in water and those in the solution, the
latter having every one of their tentacles closely inflected. Making
the moderate assumption that each of these leaves bore 160 tentacles,
each gland could have absorbed only 1/184320 of a grain (.000351 mg.).
This experiment was repeated on three leaves with the same relative
amount of the solution; and after 6 hrs. 15 m. all the tentacles except
nine, on all three leaves taken together, were closely inflected. In
this case the tentacles on each leaf were counted, and gave an average
of 162 per leaf.

The following experiments were tried during the summer of 1873, by
placing the leaves, each in a separate watch-glass and pouring over it
thirty minims (1.775 ml.) of the solution; other leaves being treated
in exactly the same manner with the doubly distilled water used in
making the solutions. The trials above given were made several years
before, and when I read over my notes, I could not believe in the
results; so I resolved to begin again with moderately strong solutions.
Six leaves were first immersed, each in thirty minims of a solution of
one part of the nitrate to 8750 of water (1 gr. to 20 oz.), so that
each received 1/320 of a grain (.2025 mg.). Before 30 m. had elapsed,
four of these leaves were immensely, and two of them moderately,
inflected. The glands were rendered of a dark red. The four
corresponding leaves in water were not at all affected until 6 hrs. had
elapsed, and then only the short tentacles on the borders of the disc;
and their inflection, as previously explained, is never of any
significance.

Four leaves were immersed, each in thirty minims of a solution of one
part to 17,500 of water (1 gr. to 40 oz.), so that each received 1/640
of a grain (.101 mg.); and in less than 45 m. three of them had all
their tentacles, except from four to ten, inflected; the blade of one
being inflected after 6 hrs., and the blade of a second after 21 hrs.
The fourth leaf was not at all affected. The glands of none were
darkened. Of the corresponding leaves [page 152] in water, only one had
any of its exterior tentacles, namely five, inflected; after 6 hrs. in
one case, and after 21 hrs. in two other cases, the short tentacles on
the borders of the disc formed a ring, in the usual manner.

Four leaves were immersed, each in thirty minims of a solution of one
part to 43,750 of water (1 gr. to 100 oz.), so that each leaf got
1/1600 of a grain (.0405 mg.). Of these, one was much inflected in 8
m., and after 2 hrs. 7 m. had all the tentacles, except thirteen,
inflected. The second leaf, after 10 m., had all except three
inflected. The third and fourth were hardly at all affected, scarcely
more than the corresponding leaves in water. Of the latter, only one
was affected, this having two tentacles inflected, with those on the
outer parts of the disc forming a ring in the usual manner. In the leaf
which had all its tentacles except three inflected in 10 m., each gland
(assuming that the leaf bore 160 tentacles) could have absorbed only
1/251200 of a grain, or .000258 mg.

Four leaves were separately immersed as before in a solution of one
part to 131,250 of water (1 gr. to 300 oz.), so that each received
1/4800 of a grain, or .0135 mg. After 50 m. one leaf had all its
tentacles except sixteen, and after 8 hrs. 20 m. all but fourteen,
inflected. The second leaf, after 40 m., had all but twenty inflected;
and after 8 hrs. 10 m. began to re-expand. The third, in 3 hrs. had
about half its tentacles inflected, which began to re-expand after 8
hrs. 15 m. The fourth leaf, after 3 hrs. 7 m., had only twenty-nine
tentacles more or less inflected. Thus three out of the four leaves
were strongly acted on. It is clear that very sensitive leaves had been
accidentally selected. The day moreover was hot. The four corresponding
leaves in water were likewise acted on rather more than is usual; for
after 3 hrs. one had nine tentacles, another four, and another two, and
the fourth none, inflected. With respect to the leaf of which all the
tentacles, except sixteen, were inflected after 50 m., each gland
(assuming that the leaf bore 160 tentacles) could have absorbed only
1/691200 of a grain (.0000937 mg.), and this appears to be about the
least quantity of the nitrate which suffices to induce the inflection
of a single tentacle.

As negative results are important in confirming the foregoing positive
ones, eight leaves were immersed as before, each in thirty minims of a
solution of one part to 175,000 of water (1 gr. to 400 oz.), so that
each received only 1/6400 of a grain (.0101 mg.). This minute quantity
produced a slight effect on only four of the eight leaves. One had
fifty-six tentacles inflected after 2 hrs. 13 m.; a second, twenty-six
inflected, or sub-inflected, after [page 153] 38 m.; a third, eighteen
inflected, after 1 hr.; and a fourth, ten inflected, after 35 m. The
four other leaves were not in the least affected. Of the eight
corresponding leaves in water, one had, after 2 hrs. 10 m., nine
tentacles, and four others from one to four long-headed tentacles,
inflected; the remaining three being unaffected. Hence, the 1/6400 of a
grain given to a sensitive leaf during warm weather perhaps produces a
slight effect; but we must bear in mind that occasionally water causes
as great an amount of inflection as occurred in this last experiment.]

A Summary of the Results with Nitrate of Ammonia.—The glands of the
disc, when excited by a half-minim drop (.0296 ml.), containing 1/2400
of a grain of the nitrate (.027 mg.), transmit a motor impulse to the
exterior tentacles, causing them to bend inwards. A minute drop,
containing 1/28800 of a grain (.00225 mg.), if held for a few seconds
in contact with a gland, causes the tentacle bearing this gland to be
inflected. If a leaf is left immersed for a few hours, and sometimes
for only a few minutes, in a solution of such strength that each gland
can absorb only the (1/691200 of a grain (.0000937 mg.), this small
amount is enough to excite each tentacle into movement, and it becomes
closely inflected.

PHOSPHATE OF AMMONIA.


This salt is more powerful than the nitrate, even in a greater degree
than the nitrate is more powerful than the carbonate. This is shown by
weaker solutions of the phosphate acting when dropped on the discs, or
applied to the glands of the exterior tentacles, or when leaves are
immersed. The difference in the power of these three salts, as tried in
three different ways, supports the results presently to be [page 154]
given, which are so surprising that their credibility requires every
kind of support. In 1872 I experimented on twelve immersed leaves,
giving each only ten minims of a solution; but this was a bad method,
for so small a quantity hardly covered them. None of these experiments
will, therefore, be given, though they indicate that excessively minute
doses are efficient. When I read over my notes, in 1873, I entirely
disbelieved them, and determined to make another set of experiments
with scrupulous care, on the same plan as those made with the nitrate;
namely by placing leaves in watch-glasses, and pouring over each thirty
minims of the solution under trial, treating at the same time and in
the same manner other leaves with the distilled water used in making
the solutions. During 1873, seventy-one leaves were thus tried in
solutions of various strengths, and the same number in water.
Notwithstanding the care taken and the number of the trials made, when
in the following year I looked merely at the results, without reading
over my observations, I again thought that there must have been some
error, and thirty-five fresh trials were made with the weakest
solution; but the results were as plainly marked as before. Altogether,
106 carefully selected leaves were tried, both in water and in
solutions of the phosphate. Hence, after the most anxious
consideration, I can entertain no doubt of the substantial accuracy of
my results.

[Before giving my experiments, it may be well to premise that
crystallised phosphate of ammonia, such as I used, contains 35.33 per
cent. of water of crystallisation; so that in all the following trials
the efficient elements formed only 64.67 per cent. of the salt used.

Extremely minute particles of the dry phosphate were placed [page 155]
with the point of a needle on the secretion surrounding several glands.
These poured forth much secretion, were blackened, and ultimately died;
but the tentacles moved only slightly. The dose, small as it was,
evidently was too great, and the result was the same as with particles
of the carbonate of ammonia.

Half-minims of a solution of one part to 437 of water were placed on
the discs of three leaves and acted most energetically, causing the
tentacles of one to be inflected in 15 m., and the blades of all three
to be much curved inwards in 2 hrs. 15 m. Similar drops of a solution
of one part to 1312 of water, (1 gr. to 3 oz.) were then placed on the
discs of five leaves, so that each received the 1/2880 of a grain
(.0225 mg.). After 8 hrs. the tentacles of four of them were
considerably inflected, and after 24 hrs. the blades of three. After 48
hrs. all five were almost fully re-expanded. I may mention with respect
to one of these leaves, that a drop of water had been left during the
previous 24 hrs. on its disc, but produced no effect; and that this was
hardly dry when the solution was added.

Similar drops of a solution of one part to 1750 of water (1 gr. to 4
oz.) were next placed on the discs of six leaves; so that each received
1/3840 of a grain (.0169 mg.); after 8 hrs. three of them had many
tentacles and their blades inflected; two others had only a few
tentacles slightly inflected, and the sixth was not at all affected.
After 24 hrs. most of the leaves had a few more tentacles inflected,
but one had begun to re-expand. We thus see that with the more
sensitive leaves the 1/3840 of a grain, absorbed by the central glands,
is enough to make many of the exterior tentacles and the blades bend,
whereas the 1/1920 of a grain of the carbonate similarly given produced
no effect; and 1/2880 of a grain of the nitrate was only just
sufficient to produce a well-marked effect.

A minute drop, about equal to 1/20 of a minim, of a solution of one
part of the phosphate to 875 of water, was applied to the secretion on
three glands, each of which thus received only 1/57600 of a grain
(.00112 mg.), and all three tentacles became inflected. Similar drops
of a solution of one part to 1312 of water (1 gr. to 3 oz.) were now
tried on three leaves; a drop being applied to four glands on the same
leaf. On the first leaf, three of the tentacles became slightly
inflected in 6 m., and re-expanded after 8 hrs. 45 m. On the second,
two tentacles became sub-inflected in 12 m. And on the third all four
tentacles were decidedly inflected in 12 m.; they remained so for 8
hrs. 30 m., but by the next morning were fully re-expanded. [page 156]
In this latter case each gland could have received only the 1/115200
(or .000563 mg.) of a grain. Lastly, similar drops of a solution of one
part to 1750 of water (1 gr. to 4 oz.) were tried on five leaves; a
drop being applied to four glands on the same leaf. The tentacles on
three of these leaves were not in the least affected; on the fourth
leaf, two became inflected; whilst on the fifth, which happened to be a
very sensitive one, all four tentacles were plainly inflected in 6 hrs.
15m.; but only one remained inflected after 24 hrs. I should, however,
state that in this case an unusually large drop adhered to the head of
the pin. Each of these glands could have received very little more than
1/153600 of a grain (or .000423); but this small quantity sufficed to
cause inflection. We must bear in mind that these drops were applied to
the viscid secretion for only from 10 to 15 seconds, and we have good
reason to believe that all the phosphate in the solution would not be
diffused and absorbed in this time. We have seen under the same
circumstances that the absorption by a gland of 1/19200 of a grain of
the carbonate, and of 1/57600 of a grain of the nitrate, did not cause
the tentacle bearing the gland in question to be inflected; so that
here again the phosphate is much more powerful than the other two
salts.

We will now turn to the 106 experiments with immersed leaves. Having
ascertained by repeated trials that moderately strong solutions were
highly efficient, I commenced with sixteen leaves, each placed in
thirty minims of a solution of one part to 43,750 of water (1 gr. to
100 oz.); so that each received 1/1600 of a grain, or .04058 mg. Of
these leaves, eleven had nearly all or a great number of their
tentacles inflected in 1 hr., and the twelfth leaf in 3 hrs. One of the
eleven had every single tentacle closely inflected in 50 m. Two leaves
out of the sixteen were only moderately affected, yet more so than any
of those simultaneously immersed in water; and the remaining two, which
were pale leaves, were hardly at all affected. Of the sixteen
corresponding leaves in water, one had nine tentacles, another six, and
two others two tentacles inflected, in the course of 5 hrs. So that the
contrast in appearance between the two lots was extremely great.

Eighteen leaves were immersed, each in thirty minims of a solution of
one part to 87,500 of water (1 gr. to 200 oz.), so that each received
1/3200 of a grain (.0202 mg.). Fourteen of these were strongly
inflected within 2 hrs., and some of them within 15 m.; three out of
the eighteen were only slightly affected, having twenty-one, nineteen,
and twelve tentacles in- [page 157] flected; and one was not at all
acted on. By an accident only fifteen, instead of eighteen, leaves were
immersed at the same time in water; these were observed for 24 hrs.;
one had six, another four, and a third two, of their outer tentacles
inflected; the remainder being quite unaffected.

The next experiment was tried under very favourable circumstances, for
the day (July 8) was very warm, and I happened to have unusually fine
leaves. Five were immersed as before in a solution of one part to
131,250 of water (1 gr. to 300 oz.), so that each received 1/4800 of a
grain, or .0135 mg. After an immersion of 25 m. all five leaves were
much inflected. After 1 hr. 25 m. one leaf had all but eight tentacles
inflected; the second, all but three; the third, all but five; the
fourth; all but twenty-three; the fifth, on the other hand, never had
more than twenty-four inflected. Of the corresponding five leaves in
water, one had seven, a second two, a third ten, a fourth one, and a
fifth none inflected. Let it be observed what a contrast is presented
between these latter leaves and those in the solution. I counted the
glands on the second leaf in the solution, and the number was 217;
assuming that the three tentacles which did not become inflected
absorbed nothing, we find that each of the 214 remaining glands could
have absorbed only 1/l027200 of a grain, or .0000631 mg. The third leaf
bore 236 glands, and subtracting the five which did not become
inflected, each of the remaining 231 glands could have absorbed only
1/1108800 of a grain (or .0000584 mg.), and this amount sufficed to
cause the tentacles to bend.

Twelve leaves were tried as before in a solution of one part to 175,000
of water (1 gr. to 400 oz.), so that each leaf received 1/6400 of a
grain (.0101 mg.). My plants were not at the time in a good state, and
many of the leaves were young and pale. Nevertheless, two of them had
all their tentacles, except three or four, closely inflected in under 1
hr. Seven were considerably affected, some within 1 hr., and others not
until 3 hrs., 4 hrs. 30 m., and 8 hrs. had elapsed; and this slow
action may be attributed to the leaves being young and pale. Of these
nine leaves, four had their blades well inflected, and a fifth slightly
so. The three remaining leaves were not affected. With respect to the
twelve corresponding leaves in water, not one had its blade inflected;
after from 1 to 2 hrs. one had thirteen of its outer tentacles
inflected; a second six, and four others either one or two inflected.
After 8 hrs. the outer tentacles did not become more inflected; whereas
this occurred with the leaves in the solution. I record in my notes
that [page 158] after the 8 hrs. it was impossible to compare the two
lots, and doubt for an instant the power of the solution.

Two of the above leaves in the solution had all their tentacles, except
three and four, inflected within an hour. I counted their glands, and,
on the same principle as before, each gland on one leaf could have
absorbed only 1/1164800, and on the other leaf only 1/1472000, of a
grain of the phosphate.

Twenty leaves were immersed in the usual manner, each in thirty minims
of a solution of one part to 218,750 of water (1 gr. to 500 oz.). So
many leaves were tried because I was then under the false impression
that it was incredible that any weaker solution could produce an
effect. Each leaf received 1/8000 of a grain, or .0081 mg. The first
eight leaves which I tried both in the solution and in water were
either young and pale or too old; and the weather was not hot. They
were hardly at all affected; nevertheless, it would be unfair to
exclude them. I then waited until I got eight pairs of fine leaves, and
the weather was favourable; the temperature of the room where the
leaves were immersed varying from 75° to 81° (23°.8 to 27°.2 Cent.) In
another trial with four pairs (included in the above twenty pairs), the
temperature in my room was rather low, about 60° (15°.5 Cent.); but the
plants had been kept for several days in a very warm greenhouse and
thus rendered extremely sensitive. Special precautions were taken for
this set of experiments; a chemist weighed for me a grain in an
excellent balance; and fresh water, given me by Prof. Frankland, was
carefully measured. The leaves were selected from a large number of
plants in the following manner: the four finest were immersed in water,
and the next four finest in the solution, and so on till the twenty
pairs were complete. The water specimens were thus a little favoured,
but they did not undergo more inflection than in the previous cases,
comparatively with those in the solution.

Of the twenty leaves in the solution, eleven became inflected within 40
m.; eight of them plainly and three rather doubtfully; but the latter
had at least twenty of their outer tentacles inflected. Owing to the
weakness of the solution, inflection occurred, except in No. 1, much
more slowly than in the previous trials. The condition of the eleven
leaves which were considerably inflected will now be given at stated
intervals, always reckoning from the time of immersion:—

(1) After only 8 m. a large number of tentacles inflected, and after 17
m. all but fifteen; after 2 hrs. all but eight in- [page 159] flected,
or plainly sub-inflected. After 4 hrs. the tentacles began to
re-expand, and such prompt re-expansion is unusual; after 7 hrs. 30 m.
they were almost fully re-expanded.

(2) After 39 m. a large number of tentacles inflected; after 2 hrs. 18
m. all but twenty-five inflected; after 4 hrs. 17 m. all but sixteen
inflected. The leaf remained in this state for many hours.

(3) After 12 m. a considerable amount of inflection; after 4 hrs. all
the tentacles inflected except those of the two outer rows, and the
leaf remained in this state for some time; after 23 hrs. began to
re-expand.

(4) After 40 m. much inflection; after 4 hrs. 13 m. fully half the
tentacles inflected; after 23 hrs. still slightly inflected.

(5) After 40 m. much inflection; after 4 hrs. 22 m. fully half the
tentacles inflected; after 23 hrs. still slightly inflected.

(6) After 40 m. some inflection; after 2 hrs. 18 m. about twenty-eight
outer tentacles inflected; after 5 hrs. 20 m. about a third of the
tentacles inflected; after 8 hrs. much re-expanded.

(7) After 20 m. some inflection; after 2 hrs. a considerable number of
tentacles inflected; after 7 hrs. 45 m. began to re-expand.

(8) After 38 m. twenty-eight tentacles inflected; after 3 hrs. 45 m.
thirty-three inflected, with most of the submarginal tentacles
sub-inflected; continued so for two days, and then partially
re-expanded.

(9) After 38 m. forty-two tentacles inflected; after 3 hrs. 12 m.
sixty-six inflected or sub-inflected; after 6 hrs. 40 m. all but
twenty-four inflected or sub-inflected; after 9 hrs. 40 m. all but
seventeen inflected; after 24 hrs. all but four inflected or
sub-inflected, only a few being closely inflected; after 27 hrs. 40 m.
the blade inflected. The leaf remained in this state for two days, and
then began to re-expand.

(10) After 38 m. twenty-one tentacles inflected; after 3 hrs. 12 m.
forty-six tentacles inflected or sub-inflected; after 6 hrs. 40 m. all
but seventeen inflected, though none closely; after 24 hrs. every
tentacle slightly curved inwards; after 27 hrs. 40 m. blade strongly
inflected, and so continued for two days, and then the tentacles and
blade very slowly re-expanded.

(11) This fine dark red and rather old leaf, though not very large,
bore an extraordinary number of tentacles (viz. 252), and behaved in an
anomalous manner. After 6 hrs. 40 m. only the short tentacles round the
outer part of the disc were inflected, forming a ring, as so often
occurs in from 8 to 24 hrs. With leaves both in water and the weaker
solutions. But after 9 hrs. [page 160] 40 m. all the outer tentacles
except twenty-five were inflected; as was the blade in a strongly
marked manner. After 24 hrs. every tentacle except one was closely
inflected, and the blade was completely doubled over. Thus the leaf
remained for two days, when it began to re-expand. I may add that the
three latter leaves (Nos. 9, 10, and 11) were still somewhat inflected
after three days. The tentacles in but few of these eleven leaves
became closelyinflected within so short a time as in the previous
experiments with stronger solutions.

We will now turn to the twenty corresponding leaves in water. Nine had
none of their outer tentacles inflected; nine others had from one to
three inflected; and these re-expanded after 8 hrs. The remaining two
leaves were moderately affected; one having six tentacles inflected in
34 m.; the other twenty-three inflected in 2 hrs. 12 m.; and both thus
remained for 24 hrs. None of these leaves had their blades inflected.
So that the contrast between the twenty leaves in water and the twenty
in the solution was very great, both within the first hour and after
from 8 to 12 hrs. had elapsed.

Of the leaves in the solution, the glands on leaf No. 1, which in 2
hrs. had all its tentacles except eight inflected, were counted and
found to be 202. Subtracting the eight, each gland could have received
only the 1/1552000 grain (.0000411 mg.) of the phosphate. Leaf No. 9
had 213 tentacles, all of which, with the exception of four, were
inflected after 24 hrs., but none of them closely; the blade was also
inflected; each gland could have received only the 1/1672000 of a
grain, or .0000387 mg. Lastly, leaf No. 11, which had after 24 hrs. all
its tentacles, except one, closely inflected, as well as the blade,
bore the unusually large number of 252 tentacles; and on the same
principle as before, each gland could have absorbed only the 1/2008000
of a grain, or .0000322 mg.

With respect to the following experiments, I must premise that the
leaves, both those placed in the solutions and in water, were taken
from plants which had been kept in a very warm greenhouse during the
winter. They were thus rendered extremely sensitive, as was shown by
water exciting them much more than in the previous experiments. Before
giving my observations, it may be well to remind the reader that,
judging from thirty-one fine leaves, the average number of tentacles is
192, and that the outer or exterior ones, the movements of which are
alone significant, are to the short ones on the disc in the proportion
of about sixteen to nine. [page 161]

Four leaves were immersed as before, each in thirty minims of a
solution of one part to 328,125 of water (1 gr. to 750 oz.). Each leaf
thus received 1/12000 of a grain (.0054 mg.) of the salt; and all four
were greatly inflected.

(1) After 1 hr. all the outer tentacles but one inflected, and the
blade greatly so; after 7 hrs. began to re-expand.

(2) After 1 hr. all the outer tentacles but eight inflected; after 12
hrs. all re-expanded.

(3) After 1 hr. much inflection; after 2 hrs. 30 m. all the tentacles
but thirty-six inflected; after 6 hrs. all but twenty-two inflected;
after 12 hrs. partly re-expanded.

(4) After 1 hr. all the tentacles but thirty-two inflected; after 2
hrs. 30 m. all but twenty-one inflected; after 6 hrs. almost
re-expanded.

Of the four corresponding leaves in water:—

(1) After 1 hr. forty-five tentacles inflected; but after 7 hrs. so
many had re-expanded that only ten remained much inflected.

(2) After 1 hr. seven tentacles inflected; these were almost
re-expanded in 6 hrs.

(3) and (4) Not affected, except that, as usual, after 11 hrs. the
short tentacles on the borders of the disc formed a ring.

There can, therefore, be no doubt about the efficiency of the above
solution; and it follows as before that each gland of No. 1 could have
absorbed only 1/2412000 of a grain (.0000268 mg.) and of No. 2 only
1/2460000 of a grain (.0000263 mg.) of the phosphate.

Seven leaves were immersed, each in thirty minims of a solution of one
part to 437,500 of water (1 gr. to 1000 oz.). Each leaf thus received
1/16000 of a grain (.00405 mg.). The day was warm, and the leaves were
very fine, so that all circumstances were favourable.

(1) After 30 m. all the outer tentacles except five inflected, and most
of them closely; after 1 hr. blade slightly inflected; after 9 hrs. 30
m. began to re-expand.

(2) After 33 m. all the outer tentacles but twenty-five inflected, and
blade slightly so; after 1 hr. 30 m. blade strongly inflected and
remained so for 24 hrs.; but some of the tentacles had then
re-expanded.

(3) After 1 hr. all but twelve tentacles inflected; after 2 hrs. 30 m.
all but nine inflected; and of the inflected tentacles all excepting
four closely; blade slightly inflected. After 8 hrs. blade quite
doubled up, and now all the tentacles excepting [page 162] eight
closely inflected. The leaf remained in this state for two days.

(4) After 2 hrs. 20 m. only fifty-nine tentacles inflected; but after 5
hrs. all the tentacles closely inflected excepting two which were not
affected, and eleven which were only sub-inflected; after 7 hrs. blade
considerably inflected; after 12 hrs. much re-expansion.

(5) After 4 hrs. all the tentacles but fourteen inflected; after 9 hrs.
30 m. beginning to re-expand.

(6) After 1 hr. thirty-six tentacles inflected; after 5 hrs. all but
fifty-four inflected; after 12 hrs. considerable re-expansion.

(7) After 4 hrs. 30 m. only thirty-five tentacles inflected or
sub-inflected, and this small amount of inflection never increased.

Now for the seven corresponding leaves in water:—

(1) After 4 hrs. thirty-eight tentacles inflected; but after 7 hrs.
these, with the exception of six, re-expanded.

(2) After 4 hrs. 20 m. twenty inflected; these after 9 hrs. partially
re-expanded.

(3) After 4 hrs. five inflected, which began to re-expand after 7 hrs.

(4) After 24 hrs. one inflected.

(5), (6) and (7) Not at all affected, though observed for 24 hrs.,
excepting the short tentacles on the borders of the disc, which as
usual formed a ring.

A comparison of the leaves in the solution, especially of the first
five or even six on the list, with those in the water, after 1 hr. or
after 4 hrs., and in a still more marked degree after 7 hrs. or 8 hrs.,
could not leave the least doubt that the solution had produced a great
effect. This was shown not only by the vastly greater number of
inflected tentacles, but by the degree or closeness of their
inflection, and by that of their blades. Yet each gland on leaf No. 1
(which bore 255 glands, all of which, excepting five, were inflected in
30 m.) could not have received more than one-four-millionth of a grain
(.0000162 mg.) of the salt. Again, each gland on leaf No. 3 (which bore
233 glands, all of which, except nine, were inflected in 2 hrs. 30 m.)
could have received at most only the 1/3584000 of a grain, or .0000181
mg.

Four leaves were immersed as before in a solution of one part to
656,250 of water (1 gr. to 1500 oz.); but on this occasion I happened
to select leaves which were very little sensitive, as on other
occasions I chanced to select unusually sensitive leaves. The leaves
were not more affected after 12 hrs. than [page 163] the four
corresponding ones in water; but after 24 hrs. they were slightly more
inflected. Such evidence, however, is not at all trustworthy.

Twelve leaves were immersed, each in thirty minims of a solution of one
part to 1,312,500 of water (1 gr. to 3000 oz.); so that each leaf
received 1/48000 of a grain (.00135 mg.). The leaves were not in very
good condition; four of them were too old and of a dark red colour;
four were too pale, yet one of these latter acted well; the four
others, as far as could be told by the eye, seemed in excellent
condition. The result was as follows:—

(1) This was a pale leaf; after 40 m. about thirty-eight tentacles
inflected; after 3 hrs. 30 m. the blade and many of the outer tentacles
inflected; after 10 hrs. 15 m. all the tentacles but seventeen
inflected, and the blade quite doubled up; after 24 hrs. all the
tentacles but ten more or less inflected. Most of them were closely
inflected, but twenty-five were only sub-inflected.

(2) After 1 hr. 40 m. twenty-five tentacles inflected; after 6 hrs. all
but twenty-one inflected; after 10 hrs. all but sixteen more or less
inflected; after 24 hrs. re-expanded.

(3) After 1 hr. 40 m. thirty-five inflected; after 6 hrs. “a large
number” (to quote my own memorandum) inflected, but from want of time
they were not counted; after 24 hrs. re-expanded.

(4) After 1 hr. 40 m. about thirty inflected; after 6 hrs. “a large
number all round the leaf” inflected, but they were not counted; after
10 hrs. began to re-expand.

(5) to (12) These were not more inflected than leaves often are in
water, having respectively 16, 8, 10, 8, 4, 9, 14, and 0 tentacles
inflected. Two of these leaves, however, were remarkable from having
their blades slightly inflected after 6 hrs.

With respect to the twelve corresponding leaves in water, (1) had,
after 1 hr. 35 m., fifty tentacles inflected, but after 11 hrs. only
twenty-two remained so, and these formed a group, with the blade at
this point slightly inflected. It appeared as if this leaf had been in
some manner accidentally excited, for instance by a particle of animal
matter which was dissolved by the water. (2) After 1 hr. 45 m.
thirty-two tentacles inflected, but after 5 hrs. 30 m. only twenty-five
inflected, and these after 10 hrs. all re-expanded; (3) after 1 hr.
twenty-five inflected, which after 10 hrs. 20 m. were all re-expanded;
(4) and (5) after 1 hr. 35 m. six and seven tentacles inflected, which
re-expanded after 11 hrs.; (6), (7) and (8) from one to three
inflected, which [page 164] soon re-expanded; (9), (10), (11) and (12)
none inflected, though observed for twenty-four hours.

Comparing the states of the twelve leaves in water with those in the
solution, there could be no doubt that in the latter a larger number of
tentacles were inflected, and these to a greater degree; but the
evidence was by no means so clear as in the former experiments with
stronger solutions. It deserves attention that the inflection of four
of the leaves in the solution went on increasing during the first 6
hrs., and with some of them for a longer time; whereas in the water the
inflection of the three leaves which were the most affected, as well as
of all the others, began to decrease during this same interval. It is
also remarkable that the blades of three of the leaves in the solution
were slightly inflected, and this is a most rare event with leaves in
water, though it occurred to a slight extent in one (No. 1), which
seemed to have been in some manner accidentally excited. All this shows
that the solution produced some effect, though less and at a much
slower rate than in the previous cases. The small effect produced may,
however, be accounted for in large part by the majority of the leaves
having been in a poor condition.

Of the leaves in the solution, No. 1 bore 200 glands and received
1/48000 of a grain of the salt. Subtracting the seventeen tentacles
which were not inflected, each gland could have absorbed only the
1/8784000 of a grain (.00000738 mg.). This amount caused the tentacle
bearing each gland to be greatly inflected. The blade was also
inflected.

Lastly, eight leaves were immersed, each in thirty minims of a solution
of one part of the phosphate to 21,875,000 of water (1 gr. to 5000
oz.). Each leaf thus received 1/80000 of a grain of the salt, or .00081
mg. I took especial pains in selecting the finest leaves from the
hot-house for immersion, both in the solution and the water, and almost
all proved extremely sensitive. Beginning as before with those in the
solution:—

(1) After 2 hrs. 30 m. all the tentacles but twenty-two inflected, but
some only sub-inflected; the blade much inflected; after 6 hrs. 30 m.
all but thirteen inflected, with the blade immensely inflected; and
remained so for 48 hrs.

(2) No change for the first 12 hrs., but after 24 hrs. all the
tentacles inflected, excepting those of the outermost row, of which
only eleven were inflected. The inflection continued to increase, and
after 48 hrs. all the tentacles except three were inflected, [page 165]
and most of them rather closely, four or five being only sub-inflected.

(3) No change for the first 12 hrs.; but after 24 hrs. all the
tentacles excepting those of the outermost row were sub-inflected, with
the blade inflected. After 36 hrs. blade strongly inflected, with all
the tentacles, except three, inflected or sub-inflected. After 48 hrs.
in the same state.

(4) to (8) These leaves, after 2 hrs. 30 m., had respectively 32, 17,
7, 4, and 0 tentacles inflected, most of which, after a few hours,
re-expanded, with the exception of No. 4, which retained its thirty-two
tentacles inflected for 48 hrs.

Now for the eight corresponding leaves in water:—

(1) After 2 hrs. 40 m. this had twenty of its outer tentacles
inflected, five of which re-expanded after 6 hrs. 30 m. After 10 hrs.
15 m. a most unusual circumstance occurred, namely, the whole blade
became slightly bowed towards the footstalk, and so remained for 48
hrs. The exterior tentacles, excepting those of the three or four
outermost rows, were now also inflected to an unusual degree.

(2) to (8) These leaves, after 2 hrs. 40 m., had respectively 42, 12,
9, 8, 2, 1, and 0 tentacles inflected, which all re-expanded within 24
hrs., and most of them within a much shorter time.

When the two lots of eight leaves in the solution and in the water were
compared after the lapse of 24 hrs., they undoubtedly differed much in
appearance. The few tentacles on the leaves in water which were
inflected had after this interval re-expanded, with the exception of
one leaf; and this presented the very unusual case of the blade being
somewhat inflected, though in a degree hardly approaching that of the
two leaves in the solution. Of these latter leaves, No. 1 had almost
all its tentacles, together with its blade, inflected after an
immersion of 2 hrs. 30 m. Leaves No. 2 and 3 were affected at a much
slower rate; but after from 24 hrs. to 48 hrs. almost all their
tentacles were closely inflected, and the blade of one quite doubled
up. We must therefore admit, incredible as the fact may at first
appear, that this extremely weak solution acted on the more sensitive
leaves; each of which received only the 1/80000 of a grain (.00081 mg.)
of the phosphate. Now, leaf No. 3 bore 178 tentacles, and subtracting
the three which were not inflected, each gland could have absorbed only
the 1/14000000 of a grain, or .00000463 mg. Leaf No. 1, which was
strongly acted on within 2 hrs. 30 m., and had all its outer tentacles,
except thirteen, inflected within 6 hrs. 30 m., bore 260 tentacles; and
on the same principle as before, each gland could have [page 166]
absorbed only 1/19760000 of a grain, or .00000328 mg.; and this
excessively minute amount sufficed to cause all the tentacles bearing
these glands to be greatly inflected. The blade was also inflected.]

A Summary of the Results with Phosphate of Ammonia.—The glands of the
disc, when excited by a half-minim drop (.0296 ml.), containing 1/3840
of a grain (.0169 mg.) of this salt, transmit a motor impulse to the
exterior tentacles, causing them to bend inwards. A minute drop,
containing 1/153600 of a grain (.000423 mg.), if held for a few seconds
in contact with a gland, causes the tentacle bearing this gland to be
inflected. If a leaf is left immersed for a few hours, and sometimes
for a shorter time, in a solution so weak that each gland can absorb
only the 1/9760000 of a grain (.00000328 mg.), this is enough to excite
the tentacle into movement, so that it becomes closely inflected, as
does sometimes the blade. In the general summary to this chapter a few
remarks will be added, showing that the efficiency of such extremely
minute doses is not so incredible as it must at first appear.

[Sulphate of Ammonia.—The few trials made with this and the following
five salts of ammonia were undertaken merely to ascertain whether they
induced inflection. Half-minims of a solution of one part of the
sulphate of ammonia to 437 of water were placed on the discs of seven
leaves, so that each received 1/960 of a grain, or .0675 mg. After 1
hr. the tentacles of five of them, as well as the blade of one, were
strongly inflected. The leaves were not afterwards observed.

Citrate of Ammonia.—Half-minims of a solution of one part to 437 of
water were placed on the discs of six leaves. In 1 hr. the short outer
tentacles round the discs were a little inflected, with the glands on
the discs blackened. After 3 hrs. 25 m. one leaf had its blade
inflected, but none of the exterior tentacles. All six leaves remained
in nearly the same state during the day, the submarginal tentacles,
however, [page 167] becoming more inflected. After 23 hrs. three of the
leaves had their blades somewhat inflected; and the submarginal
tentacles of all considerably inflected, but in none were the two,
three, or four outer rows affected. I have rarely seen cases like this,
except from the action of a decoction of grass. The glands on the discs
of the above leaves, instead of being almost black, as after the first
hour, were now after 23 hrs. very pale. I next tried on four leaves
half-minims of a weaker solution, of one part to 1312 of water (1 gr.
to 3 oz.); so that each received 1/2880 of a grain (.0225 mg.). After 2
hrs. 18 m. the glands on the disc were very dark-coloured; after 24
hrs. two of the leaves were slightly affected; the other two not at
all.

Acetate of Ammonia.—Half-minims of a solution of about one part to 109
of water were placed on the discs of two leaves, both of which were
acted on in 5 hrs. 30 m., and after 23 hrs. had every single tentacle
closely inflected.

Oxalate of Ammonia.—Half-minims of a solution of one part to 218 of
water were placed on two leaves, which, after 7 hrs., became
moderately, and after 23 hrs. strongly, inflected. Two other leaves
were tried with a weaker solution of one part to 437 of water; one was
strongly inflected in 7 hrs.; the other not until 30 hrs. had elapsed.

Tartrate of Ammonia.—Half-minims of a solution of one part to 437 of
water were placed on the discs of five leaves. In 31 m. there was a
trace of inflection in the exterior tentacles of some of the leaves,
and this became more decided after 1 hr. with all the leaves; but the
tentacles were never closely inflected. After 8 hrs. 30 m. they began
to re-expand. Next morning, after 23 hrs., all were fully re-expanded,
excepting one which was still slightly inflected. The shortness of the
period of inflection in this and the following case is remarkable.

Chloride of Ammonium.—Half-minims of a solution of one part to 437 of
water were placed on the discs of six leaves. A decided degree of
inflection in the outer and submarginal tentacles was perceptible in 25
m.; and this increased during the next three or four hours, but never
became strongly marked. After only 8 hrs. 30 m. the tentacles began to
re-expand, and by the next morning, after 24 hrs., were fully
re-expanded on four of the leaves, but still slightly inflected on
two.]

General Summary and Concluding Remarks on the Salts of Ammonia.—We have
now seen that the nine [page 168] salts of ammonia which were tried,
all cause the inflection of the tentacles, and often of the blade of
the leaf. As far as can be ascertained from the superficial trials with
the last six salts, the citrate is the least powerful, and the
phosphate certainly by far the most. The tartrate and chloride are
remarkable from the short duration of their action. The relative
efficiency of the carbonate, nitrate, and phosphate, is shown in the
following table by the smallest amount which suffices to cause the
inflection of the tentacles.

Column 1 : Solutions, how applied. Column 2 : Carbonate of Ammonia.
Column 3 : Nitrate of Ammonia. Column 4 : Phosphate of Ammonia.

Placed on the glands of the disc, so as to act indirectly on the outer
tentacles : 1/960 of a grain, or 0675 mg. : 1/2400 of a grain, or .027
mg. : 1/3840 of a grain, or .0169 mg.

Applied for a few seconds directly to the gland of an outer tentacle :
1/14400 of a grain, or .00445 mg. : 1/28800 of a grain, or .0025 mg.
grain, 1/153600 of a grain, or .000423 mg.

Leaf immersed, with time allowed for each gland to absorb all that it
can : 1/268800 of a grain, or .00024 mg. : 1/691200 of a grain, or
.0000937 mg. : 1/19760000 of a grain, or .00000328 mg.

Amount absorbed by a gland which suffices to cause the aggregation of
the protoplasm in the adjoining cells of the tentacles. 1/134400 of a
grain, or .00048 mg.

From the experiments tried in these three different ways, we see that
the carbonate, which contains 23.7 per cent. of nitrogen, is less
efficient than the nitrate, which contains 35 per cent. The phosphate
contains less nitrogen than either of these salts, namely, only 21.2
per cent., and yet is far more [page 169] efficient; its power no doubt
depending quite as much on the phosphorus as on the nitrogen which it
contains. We may infer that this is the case, from the energetic manner
in which bits of bone and phosphate of lime affect the leaves. The
inflection excited by the other salts of ammonia is probably due solely
to their nitrogen,—on the same principle that nitrogenous organic
fluids act powerfully, whilst non-nitrogenous organic fluids are
powerless. As such minute doses of the salts of ammonia affect the
leaves, we may feel almost sure that Drosera absorbs and profits by the
amount, though small, which is present in rain-water, in the same
manner as other plants absorb these same salts by their roots.

The smallness of the doses of the nitrate, and more especially of the
phosphate of ammonia, which cause the tentacles of immersed leaves to
be inflected, is perhaps the most remarkable fact recorded in this
volume. When we see that much less than the millionth* of a grain of
the phosphate, absorbed by a gland of one of the exterior tentacles,
causes it to bend, it may be thought that the effects of the solution
on the glands of the disc have been overlooked; namely, the
transmission of a motor impulse from them to the exterior tentacles. No
doubt the movements of the latter are thus aided; but the aid thus
rendered must be insignificant; for we know that a drop containing as
much as the 1/3840 of a grain placed on the disc is only just able to
cause the outer tentacles of a highly sensitive leaf to bend. It is
cer-

* It is scarcely possible to realise what a million means. The best
illustration which I have met with is that given by Mr. Croll, who
says,—Take a narrow strip of paper 83 ft. 4 in. in length, and stretch
it along the wall of a large hall; then mark off at one end the tenth
of an inch. This tenth will represent a hundred, and the entire strip a
million. [page 170]


tainly a most surprising fact that the 1/19760000 of a grain, or in
round numbers the one-twenty-millionth of a grain (.0000033 mg.), of
the phosphate should affect any plant, or indeed any animal; and as
this salt contains 35.33 per cent. of water of crystallisation, the
efficient elements are reduced to 1/30555126 of a grain, or in round
numbers to one-thirty-millionth of a grain (.00000216 mg.). The
solution, moreover, in these experiments was diluted in the proportion
of one part of the salt to 2,187,500 of water, or one grain to 5000 oz.
The reader will perhaps best realise this degree of dilution by
remembering that 5000 oz. would more than fill a 31-gallon cask; and
that to this large body of water one grain of the salt was added; only
half a drachm, or thirty minims, of the solution being poured over a
leaf. Yet this amount sufficed to cause the inflection of almost every
tentacle, and often of the blade of the leaf.

I am well aware that this statement will at first appear incredible to
almost everyone. Drosera is far from rivalling the power of the
spectroscope, but it can detect, as shown by the movements of its
leaves, a very much smaller quantity of the phosphate of ammonia than
the most skilful chemist can of any substance.* My results were for a
long time incredible

* When my first observations were made on the nitrate of ammonia,
fourteen years ago, the powers of the spectroscope had not been
discovered; and I felt all the greater interest in the then unrivalled
powers of Drosera. Now the spectroscope has altogether beaten Drosera;
for according to Bunsen and Kirchhoff probably less than one
1/200000000 of a grain of sodium can be thus detected (see Balfour
Stewart, ‘Treatise on Heat,’ 2nd edit. 1871, p. 228). With respect to
ordinary chemical tests, I gather from Dr. Alfred Taylor’s work on
‘Poisons’ that about 1/4000 of a grain of arsenic, 1/4400 of a grain of
prussic acid, 1/1400 of iodine, and 1/2000 of tartarised antimony, can
be detected; but the power of detection depends much on the solutions
under trial not being extremely weak. [page 171]


even to myself, and I anxiously sought for every source of error. The
salt was in some cases weighed for me by a chemist in an excellent
balance; and fresh water was measured many times with care. The
observations were repeated during several years. Two of my sons, who
were as incredulous as myself, compared several lots of leaves
simultaneously immersed in the weaker solutions and in water, and
declared that there could be no doubt about the difference in their
appearance. I hope that some one may hereafter be induced to repeat my
experiments; in this case he should select young and vigorous leaves,
with the glands surrounded by abundant secretion. The leaves should be
carefully cut off and laid gently in watch-glasses, and a measured
quantity of the solution and of water poured over each. The water used
must be as absolutely pure as it can be made. It is to be especially
observed that the experiments with the weaker solutions ought to be
tried after several days of very warm weather. Those with the weakest
solutions should be made on plants which have been kept for a
considerable time in a warm greenhouse, or cool hothouse; but this is
by no means necessary for trials with solutions of moderate strength.

I beg the reader to observe that the sensitiveness or irritability of
the tentacles was ascertained by three different methods—indirectly by
drops placed on the disc, directly by drops applied to the glands of
the outer tentacles, and by the immersion of whole leaves; and it was
found by these three methods that the nitrate was more powerful than
the carbonate, and the phosphate much more powerful than the nitrate;
this result being intelligible from the difference in the amount of
nitrogen in the first two salts, and from the presence of phosphorus in
the third. It may aid the [page 172] reader’s faith to turn to the
experiments with a solution of one grain of the phosphate to 1000 oz.
of water, and he will there find decisive evidence that the
one-four-millionth of a grain is sufficient to cause the inflection of
a single tentacle. There is, therefore, nothing very improbable in the
fifth of this weight, or the one-twenty-millionth of a grain, acting on
the tentacle of a highly sensitive leaf. Again, two of the leaves in
the solution of one grain to 3000 oz., and three of the leaves in the
solution of one grain to 5000 oz., were affected, not only far more
than the leaves tried at the same time in water, but incomparably more
than any five leaves which can be picked out of the 173 observed by me
at different times in water.

There is nothing remarkable in the mere fact of the
one-twenty-millionth of a grain of the phosphate, dissolved in above
two-million times its weight of water, being absorbed by a gland. All
physiologists admit that the roots of plants absorb the salts of
ammonia brought to them by the rain; and fourteen gallons of rain-water
contain* a grain of ammonia, therefore only a little more than twice as
much as in the weakest solution employed by me. The fact which appears
truly wonderful is, that the one-twenty-millionth of a grain of the
phosphate of ammonia (including less than the one-thirty-millionth of
efficient matter), when absorbed by a gland, should induce some change
in it, which leads to a motor impulse being transmitted down the whole
length of the tentacle, causing the basal part to bend, often through
an angle of above 180 degrees.

Astonishing as is this result, there is no sound reason

* Miller’s ‘Elements of Chemistry,’ part ii. p. 107, 3rd edit. 1864.
[page 173]


why we should reject it as incredible. Prof. Donders, of Utrecht,
informs me that from experiments formerly made by him and Dr. De
Ruyter, he inferred that less than the one-millionth of a grain of
sulphate of atropine, in an extremely diluted state, if applied
directly to the iris of a dog, paralyses the muscles of this organ.
But, in fact, every time that we perceive an odour, we have evidence
that infinitely smaller particles act on our nerves. When a dog stands
a quarter of a mile to leeward of a deer or other animal, and perceives
its presence, the odorous particles produce some change in the
olfactory nerves; yet these particles must be infinitely smaller* than
those of the phosphate of ammonia weighing the one-twenty-millionth of
a grain. These nerves then transmit some influence to the brain of the
dog, which leads to action on its part. With Drosera, the really
marvellous fact is, that a plant without any specialised nervous system
should be affected by such minute particles; but we have no grounds for
assuming that other tissues could not be rendered as exquisitely
susceptible to impressions from without if this were beneficial to the
organism, as is the nervous system of the higher animals.

* My son, George Darwin, has calculated for me the diameter of a sphere
of phosphate of ammonia (specific gravity 1.678), weighing the
one-twenty-millionth of a grain, and finds it to be 1/1644 of an inch.
Now, Dr. Klein informs me that the smallest Micrococci, which are
distinctly discernible under a power of 800 diameters, are estimated to
be from .0002 to .0005 of a millimetre—that is, from 1/50800 to
1/127000 of an inch—in diameter. Therefore, an object between 1/31 and
1/77 of the size of a sphere of the phosphate of ammonia of the above
weight can be seen under a high power; and no one supposes that odorous
particles, such as those emitted from the deer in the above
illustration, could be seen under any power of the microscope.) [page
174]




CHAPTER VIII.
THE EFFECTS OF VARIOUS OTHER SALTS AND ACIDS ON THE LEAVES.


Salts of sodium, potassium, and other alkaline, earthy, and metallic
salts—Summary on the action of these salts—Various acids—Summary on
their action.


Having found that the salts of ammonia were so powerful, I was led to
investigate the action of some other salts. It will be convenient,
first, to give a list of the substances tried (including forty-nine
salts and two metallic acids), divided into two columns, showing those
which cause inflection, and those which do not do so, or only
doubtfully. My experiments were made by placing half-minim drops on the
discs of leaves, or, more commonly, by immersing them in the solutions;
and sometimes by both methods. A summary of the results, with some
concluding remarks, will then be given. The action of various acids
will afterwards be described.

COLUMN 1 : SALTS CAUSING INFLECTION. COLUMN 2 : SALTS NOT CAUSING
INFLECTION.

(Arranged in Groups according to the Chemical Classification in Watts’
‘Dictionary of Chemistry.’)

Sodium carbonate, rapid inflection. : Potassium carbonate: slowly
poisonous. Sodium nitrate, rapid inflection. : Potassium nitrate:
somewhat poisonous. Sodium sulphate, moderately rapid inflection. :
Potassium sulphate. Sodium phosphate, very rapid inflection. :
Potassium phosphate. Sodium citrate, rapid inflection. : Potassium
citrate. Sodium oxalate; rapid inflection. Sodium chloride, moderately
rapid inflection. : Potassium chloride. [page 175]

COLUMN 1 : SALTS CAUSING INFLECTION. COLUMN 2 : SALTS NOT CAUSING
INFLECTION.

(Arranged in Groups according to the Chemical Classification in Watts’
‘Dictionary of Chemistry.’)

Sodium iodide, rather slow inflection. : Potassium iodide, a slight and
doubtful amount of inflection. Sodium bromide, moderately rapid
inflection. : Potassium bromide. Potassium oxalate, slow and doubtful
inflection. : Lithium nitrate, moderately rapid inflection. : Lithium
acetate. Caesium chloride, rather slow inflection. : Rubidium chloride.
Silver nitrate, rapid inflection: quick poison. : Cadmium chloride,
slow inflection. : Calcium acetate. Mercury perchloride, rapid
inflection: quick poison. : Calcium nitrate. : Magnesium acetate. :
Magnesium nitrate. : Magnesium chloride. : Magnesium sulphate. : Barium
acetate. : Barium nitrate. : Strontium acetate. : Strontium nitrate. :
Zinc chloride.


Aluminium chloride, slow and doubtful inflection. : Aluminium nitrate,
a trace of inflection. Gold chloride, rapid inflection: quick poison. :
Aluminium and potassium sulphate.

Tin chloride, slow inflection: poisonous. : Lead chloride.

Antimony tartrate, slow inflection: probably poisonous. Arsenious acid,
quick inflection: poisonous. Iron chloride, slow inflection: probably
poisonous. : Manganese chloride. Chromic acid, quick inflection: highly
poisonous. Copper chloride, rather slow in flection: poisonous. :
Cobalt chloride. Nickel chloride, rapid inflection: probably poisonous.
Platinum chloride, rapid inflection: poisonous. [page 176]

Sodium, Carbonate of (pure, given me by Prof. Hoffmann).—Half-minims
(.0296 ml.) of a solution of one part to 218 of water (2 grs. to 1 oz.)
were placed on the discs of twelve leaves. Seven of these became well
inflected; three had only two or three of their outer tentacles
inflected, and the remaining two were quite unaffected. But the dose,
though only the 1/480 of a grain (.135 mg.), was evidently too strong,
for three of the seven well-inflected leaves were killed. On the other
hand, one of the seven, which had only a few tentacles inflected,
re-expanded and seemed quite healthy after 48 hrs. By employing a
weaker solution (viz. one part to 437 of water, or 1 gr. to 1 oz.),
doses of 1/960 of a grain (.0675 mg.) were given to six leaves. Some of
these were affected in 37 m.; and in 8 hrs. the outer tentacles of all,
as well as the blades of two, were considerably inflected. After 23
hrs. 15 m. the tentacles had almost re-expanded, but the blades of the
two were still just perceptibly curved inwards. After 48 hrs. all six
leaves were fully re-expanded, and appeared perfectly healthy.

Three leaves were immersed, each in thirty minims of a solution of one
part to 875 of water (1 gr. to 2 oz.), so that each received 1/32 of a
grain (2.02 mg.); after 40 m. the three were much affected, and after 6
hrs. 45 m. the tentacles of all and the blade of one closely inflected.

Sodium, Nitrate of (pure).—Half-minims of a solution of one part to 437
of water, containing 1/960 of a grain (.0675 mg.), were placed on the
discs of five leaves. After 1 hr. 25 m. the tentacles of nearly all,
and the blade of one, were somewhat inflected. The inflection continued
to increase, and in 21 hrs. 15 m. the tentacles and the blades of four
of them were greatly affected, and the blade of the fifth to a slight
extent. After an additional 24 hrs. the four leaves still remained
closely inflected, whilst the fifth was beginning to expand. Four days
after the solution had been applied, two of the leaves had quite, and
one had partially, re-expanded; whilst the remaining two remained
closely inflected and appeared injured.

Three leaves were immersed, each in thirty minims of a solution of one
part to 875 of water; in 1 hr. there was great inflection, and after 8
hrs. 15 m. every tentacle and the blades of all three were most
strongly inflected.

Sodium, Sulphate of.—Half-minims of a solution of one part to 437 of
water were placed on the discs of six leaves. After 5 hrs. 30 m. the
tentacles of three of them, (with the blade of one) were considerably;
and those of the other three slightly, inflected. After 21 hrs. the
inflection had a little decreased, [page 177] and in 45 hrs. the leaves
were fully expanded, appearing quite healthy.

Three leaves were immersed, each in thirty minims of a solution of one
part of the sulphate to 875 of water; after 1 hr. 30 m. there was some
inflection, which increased so much that in 8 hrs. 10 m. all the
tentacles and the blades of all three leaves were closely inflected.

Sodium, Phosphate of.—Half-minims of a solution of one part to 437 of
water were placed on the discs of six leaves. The solution acted with
extraordinary rapidity, for in 8 m. the outer tentacles on several of
the leaves were much incurved. After 6 hrs. the tentacles of all six
leaves, and the blades of two, were closely inflected. This state of
things continued for 24 hrs., excepting that the blade of a third leaf
became incurved. After 48 hrs. all the leaves re-expanded. It is clear
that 1/960 of a grain of phosphate of soda has great power in causing
inflection.

Sodium, Citrate of.—Half-minims of a solution of one part to 437 of
water were placed on the discs of six leaves, but these were not
observed until 22 hrs. had elapsed. The sub-marginal tentacles of five
of them, and the blades of four, were then found inflected; but the
outer rows of tentacles were not affected. One leaf, which appeared
older than the others, was very little affected in any way. After 46
hrs. four of the leaves were almost re-expanded, including their
blades. Three leaves were also immersed, each in thirty minims of a
solution of one part of the citrate to 875 of water; they were much
acted on in 25 m.; and after 6 hrs. 35 m. almost all the tentacles,
including those of the outer rows, were inflected, but not the blades.

Sodium, Oxalate of.—Half-minims of a solution of one part to 437 of
water were placed on the discs of seven leaves; after 5 hrs. 30 m. the
tentacles of all, and the blades of most of them, were much affected.
In 22 hrs., besides the inflection of the tentacles, the blades of all
seven leaves were so much doubled over that their tips and bases almost
touched. On no other occasion have I seen the blades so strongly
affected. Three leaves were also immersed, each in thirty minims of a
solution of one part to 875 of water; after 30 m. there was much
inflection, and after 6 hrs. 35 m. the blades of two and the tentacles
of all were closely inflected.

Sodium, Chloride of (best culinary salt).—Half-minims of a solution of
one part to 218 of water were placed on the discs [page 178] of four
leaves. Two, apparently, were not at all affected in 48 hrs.; the third
had its tentacles slightly inflected; whilst the fourth had almost all
its tentacles inflected in 24 hrs., and these did not begin to
re-expand until the fourth day, and were not perfectly expanded on the
seventh day. I presume that this leaf was injured by the salt.
Half-minims of a weaker solution, of one part to 437 of water, were
then dropped on the discs of six leaves, so that each received 1/960 of
a grain. In 1 hr. 33 m. there was slight inflection; and after 5 hrs.
30 m. the tentacles of all six leaves were considerably, but not
closely, inflected. After 23 hrs. 15 m. all had completely re-expanded,
and did not appear in the least injured.

Three leaves were immersed, each in thirty minims of a solution of one
part to 875 of water, so that each received 1/32 of a grain, or 2.02
mg. After 1 hr. there was much inflection; after 8 hrs. 30 m. all the
tentacles and the blades of all three were closely inflected. Four
other leaves were also immersed in the solution, each receiving the
same amount of salt as before, viz. 1/32 of a grain. They all soon
became inflected; after 48 hrs. they began to re-expand, and appeared
quite uninjured, though the solution was sufficiently strong to taste
saline.

Sodium, Iodide of.—Half-minims of a solution of one part to 437 of
water were placed on the discs of six leaves. After 24 hrs. four of
them had their blades and many tentacles inflected. The other two had
only their submarginal tentacles inflected; the outer ones in most of
the leaves being but little affected. After 46 hrs. the leaves had
nearly re-expanded. Three leaves were also immersed, each in thirty
minims of a solution of one part to 875 of water. After 6 hrs. 30 m.
almost all the tentacles, and the blade of one leaf, were closely
inflected.

Sodium, Bromide of.—Half-minims of a solution of one part to 437 of
water were placed on six leaves. After 7 hrs. there was some
inflection; after 22 hrs. three of the leaves had their blades and most
of their tentacles inflected; the fourth leaf was very slightly, and
the fifth and sixth hardly at all, affected. Three leaves were also
immersed, each in thirty minims of a solution of one part to 875 of
water; after 40 m. there was some inflection; after 4 hrs. the
tentacles of all three leaves and the blades of two were inflected.
These leaves were then placed in water, and after 17 hrs. 30 m. two of
them were almost completely, and the third partially, re-expanded; so
that apparently they were not injured. [page 179]

Potassium, Carbonate of (pure).—Half-minims of a solution of one part
to 437 of water were placed on six leaves. No effect was produced in 24
hrs.; but after 48 hrs. some of the leaves had their tentacles, and one
the blade, considerably inflected. This, however, seemed the result of
their being injured; for on the third day after the solution was given,
three of the leaves were dead, and one was very unhealthy; the other
two were recovering, but with several of their tentacles apparently
injured, and these remained permanently inflected. It is evident that
the 1/960 of a grain of this salt acts as a poison. Three leaves were
also immersed, each in thirty minims of a solution of one part to 875
of water, though only for 9 hrs.; and, very differently from what
occurs with the salts of soda, no inflection ensued.

Potassium, Nitrate of.—Half-minims of a strong solution, of one part to
109 of water (4 grs. to 1 oz.), were placed on the discs of four
leaves; two were much injured, but no inflection ensued. Eight leaves
were treated in the same manner, with drops of a weaker solution, of
one part to 218 of water. After 50 hrs. there was no inflection, but
two of the leaves seemed injured. Five of these leaves were
subsequently tested with drops of milk and a solution of gelatine on
their discs, and only one became inflected; so that the solution of the
nitrate of the above strength, acting for 50 hrs., apparently had
injured or paralysed the leaves. Six leaves were then treated in the
same manner with a still weaker solution, of one part to 437 of water,
and these, after 48 hrs., were in no way affected, with the exception
of perhaps a single leaf. Three leaves were next immersed for 25 hrs.,
each in thirty minims of a solution of one part to 875 of water, and
this produced no apparent effect. They were then put into a solution of
one part of carbonate of ammonia to 218 of water; the glands were
immediately blackened, and after 1 hr. there was some inflection, and
the protoplasmic contents of the cells became plainly aggregated. This
shows that the leaves had not been much injured by their immersion for
25 hrs. in the nitrate.

Potassium, Sulphate of.—Half-minims of a solution of one part to 437 of
water were placed on the discs of six leaves. After 20 hrs. 30 m. no
effect was produced; after an additional 24 hrs. three remained quite
unaffected; two seemed injured, and the sixth seemed almost dead with
its tentacles inflected. Nevertheless, after two additional days, all
six leaves recovered. The immersion of three leaves for 24 hrs., each
in thirty minims of [page 180] a solution of one part to 875 of water,
produced no apparent effect. They were then treated with the same
solution of carbonate of ammonia, with the same result as in the case
of the nitrate of potash.

Potassium, Phosphate of.—Half-minims of a solution of one part to 437
of water were placed on the discs of six leaves, which were observed
during three days; but no effect was produced. The partial drying up of
the fluid on the disc slightly drew together the tentacles on it, as
often occurs in experiments of this kind. The leaves on the third day
appeared quite healthy.

Potassium, Citrate of.—Half-minims of a solution of one part to 437 of
water, left on the discs of six leaves for three days, and the
immersion of three leaves for 9 hrs., each in 30 minims of a solution
of one part to 875 of water, did not produce the least effect.

Potassium, Oxalate of.—Half-minims were placed on different occasions
on the discs of seventeen leaves; and the results perplexed me much, as
they still do. Inflection supervened very slowly. After 24 hrs. four
leaves out of the seventeen were well inflected, together with the
blades of two; six were slightly affected, and seven not at all. Three
leaves of one lot were observed for five days, and all died; but in
another lot of six, all excepting one looked healthy after four days.
Three leaves were immersed during 9 hrs., each in 30 minims of a
solution of one part to 875 of water, and were not in the least
affected; but they ought to have been observed for a longer time.

Potassium, Chloride of. Neither half-minims of a solution of one part
to 437 of water; left on the discs of six leaves for three days, nor
the immersion of three leaves during 25 hrs., in 30 minims of a
solution of one part to 875 of water, produced the least effect. The
immersed leaves were then treated with carbonate of ammonia, as
described under nitrate of potash, and with the same result.

Potassium, Iodide of.—Half-minims of a solution of one part to 437 of
water were placed on the discs of seven leaves. In 30 m. one leaf had
the blade inflected; after some hours three leaves had most of their
submarginal tentacles moderately inflected; the remaining three being
very slightly affected. Hardly any of these leaves had their outer
tentacles inflected. After 21 hrs. all re-expanded, excepting two which
still had a few submarginal tentacles inflected. Three leaves were next
[page 181] immersed for 8 hrs. 40 m., each in 30 minims of a solution
of one part to 875 of water, and were not in the least affected. I do
not know what to conclude from this conflicting evidence; but it is
clear that the iodide of potassium does not generally produce any
marked effect.

Potassium, Bromide of.—Half-minims of a solution of one part to 437 of
water were placed on the discs of six leaves; after 22 hrs. one had its
blade and many tentacles inflected, but I suspect that an insect might
have alighted on it and then escaped; the five other leaves were in no
way affected. I tested three of these leaves with bits of meat, and
after 24 hrs. they became splendidly inflected. Three leaves were also
immersed for 21 hrs. in 30 minims of a solution of one part to 875 of
water; but they were not at all affected, excepting that the glands
looked rather pale.

Lithium, Acetate of.—Four leaves were immersed together in a vessel
containing 120 minims of a solution of one part to 437 of water; so
that each received, if the leaves absorbed equally, 1/16 of a grain.
After 24 hrs. there was no inflection. I then added, for the sake of
testing the leaves, some strong solution (viz. 1 gr. to 20 oz., or one
part to 8750 of water) of phosphate of ammonia, and all four became in
30 m. closely inflected.

Lithium, Nitrate of.—Four leaves were immersed, as in the last case, in
120 minims of a solution of one part to 437 of water; after 1 h. 30 m.
all four were a little, and after 24 hrs. greatly, inflected. I then
diluted the solution with some water, but they still remained somewhat
inflected on the third day.

Caesium, Chloride of.—Four leaves were immersed, as above, in 120
minims of a solution of one part to 437 of water. After 1 hr. 5 m. the
glands were darkened; after 4 hrs. 20 m. there was a trace of
inflection; after 6 hrs. 40 m. two leaves were greatly, but not
closely, and the other two considerably inflected. After 22 hrs. the
inflection was extremely great, and two had their blades inflected. I
then transferred the leaves into water, and in 46 hrs. from their first
immersion they were almost re-expanded.

Rubidium, Chloride of.—Four leaves which were immersed, as above, in
120 minims of a solution of one part to 437 of water, were not acted on
in 22 hrs. I then added some of the strong solution (1 gr. to 20 oz.)
of phosphate of ammonia, and in 30 m. all were immensely inflected.

Silver, Nitrate of.—Three leaves were immersed in ninety [page 182]
minims of a solution of one part to 437 of water; so that each
received, as before, 1/16 of a grain. After 5 m. slight inflection, and
after 11 m. very strong inflection, the glands becoming excessively
black; after 40 m. all the tentacles were closely inflected. After 6
hrs. the leaves were taken out of the solution, washed, and placed in
water; but next morning they were evidently dead.

Calcium, Acetate of.—Four leaves were immersed in 120 minims of a
solution of one part to 437 of water; after 24 hrs. none of the
tentacles were inflected, excepting a few where the blade joined the
petiole; and this may have been caused by the absorption of the salt by
the cut-off end of the petiole. I then added some of the solution (1
gr. to 20 oz.) of phosphate of ammonia, but this to my surprise excited
only slight inflection, even after 24 hrs. Hence it would appear that
the acetate had rendered the leaves torpid.

Calcium, Nitrate of.—Four leaves were immersed in 120 minims of a
solution of one part to 437 of water, but were not affected in 24 hrs.
I then added some of the solution of phosphate of ammonia (1 gr. to 20
oz.), but this caused only very slight inflection after 24 hrs. A fresh
leaf was next put into a mixed solution of the above strengths of the
nitrate of calcium and phosphate of ammonia, and it became closely
inflected in between 5 m. and 10 m. Half-minims of a solution of one
part of the nitrate of calcium to 218 of water were dropped on the
discs of three leaves, but produced no effect.

Magnesium, Acetate, Nitrate, and Chloride of.—Four leaves were immersed
in 120 minims of solutions, of one part to 437 of water, of each of
these three salts; after 6 hrs. there was no inflection; but after 22
hrs. one of the leaves in the acetate was rather more inflected than
generally occurs from an immersion for this length of time in water.
Some of the solution (1 gr. to 20 oz.) of phosphate of ammonia was then
added to the three solutions. The leaves in the acetate mixed with the
phosphate underwent some inflection; and this was well pronounced after
24 hrs. Those in the mixed nitrate were decidedly inflected in 4 hrs.
30 m., but the degree of inflection did not afterwards much increase;
whereas the four leaves in the mixed chloride were greatly inflected in
a few minutes, and after 4 hrs. had almost every tentacle closely
inflected. We thus see that the acetate and nitrate of magnesium injure
the leaves, or at least prevent the subsequent action of phosphate of
ammonia; whereas the chloride has no such tendency. [page 183]

Magnesium, Sulphate of.—Half-minims of a solution of one part to 218 of
water were placed on the discs of ten leaves, and produced no effect.

Barium, Acetate of.—Four leaves were immersed in 120 minims of a
solution of one part to 437 of water, and after 22 hrs. there was no
inflection, but the glands were blackened. The leaves were then placed
in a solution (1 gr. to 20 oz.) of phosphate of ammonia, which caused
after 26 hrs. only a little inflection in two of the leaves.

Barium, Nitrate of.—Four leaves were immersed in 120 minims of a
solution of one part to 437 of water; and after 22 hrs. there was no
more than that slight degree of inflection, which often follows from an
immersion of this length in pure water. I then added some of the same
solution of phosphate of ammonia, and after 30 m. one leaf was greatly
inflected, two others moderately, and the fourth not at all. The leaves
remained in this state for 24 hrs.

Strontium, Acetate of.—Four leaves, immersed in 120 minims of a
solution of one part to 437 of water, were not affected in 22 hrs. They
were then placed in some of the same solution of phosphate of ammonia,
and in 25 m. two of them were greatly inflected; after 8 hrs. the third
leaf was considerably inflected, and the fourth exhibited a trace of
inflection. They were in the same state next morning.

Strontium, Nitrate of.—Five leaves were immersed in 120 minims of a
solution of one part to 437 of water; after 22 hrs. there was some
slight inflection, but not more than sometimes occurs with leaves in
water. They were then placed in the same solution of phosphate of
ammonia; after 8 hrs. three of them were moderately inflected, as were
all five after 24 hrs.; but not one was closely inflected. It appears
that the nitrate of strontium renders the leaves half torpid.

Cadmium, Chloride of.—Three leaves were immersed in ninety minims of a
solution of one part to 437 of water; after 5 hrs. 20 m. slight
inflection occurred, which increased during the next three hours. After
24 hrs. all three leaves had their tentacles well inflected, and
remained so for an additional 24 hrs.; glands not discoloured.

Mercury, Perchloride of.—Three leaves were immersed in ninety minims of
a solution of one part to 437 of water; after 22 m. there was some
slight inflection, which in 48 m. became well pronounced; the glands
were now blackened. After 5 hrs. 35 m. all the tentacles closely
inflected; after 24 hrs. still [page 184] inflected and discoloured.
The leaves were then removed and left for two days in water; but they
never re-expanded, being evidently dead.

Zinc, Chloride of.—Three leaves immersed in ninety minims of a solution
of one part to 437 of water were not affected in 25 hrs. 30 m.

Aluminium, Chloride of.—Four leaves were immersed in 120 minims of a
solution of one part to 437 of water; after 7 hrs. 45 m. no inflection;
after 24 hrs. one leaf rather closely, the second moderately, the third
and fourth hardly at all, inflected. The evidence is doubtful, but I
think some power in slowly causing inflection must be attributed to
this salt. These leaves were then placed in the solution (1 gr. to 20
oz.) of phosphate of ammonia, and after 7 hrs. 30 m. the three, which
had been but little affected by the chloride, became rather closely
inflected.

Aluminium, Nitrate of.—Four leaves were immersed in 120 minims of a
solution of one part to 437 of water; after 7 hrs. 45 m. there was only
a trace of inflection; after 24 hrs. one leaf was moderately inflected.
The evidence is here again doubtful, as in the case of the chloride of
aluminium. The leaves were then transferred to the same solution, as
before, of phosphate of ammonia; this produced hardly any effect in 7
hrs. 30 m.; but after 25 hrs. one leaf was pretty closely inflected,
the three others very slightly, perhaps not more so than from water.

Aluminium and Potassium, Sulphate of (common alum).—Half-minims of a
solution of the usual strength were placed on the discs of nine leaves,
but produced no effect.

Gold, Chloride of.—Seven leaves were immersed in so much of a solution
of one part to 437 of water that each received 30 minims, containing
1/16 of a grain, or 4.048 mg., of the chloride. There was some
inflection in 8 m., which became extreme in 45 m. In 3 hrs. the
surrounding fluid was coloured purple, and the glands were blackened.
After 6 hrs. the leaves were transferred to water; next morning they
were found discoloured and evidently killed. The secretion decomposes
the chloride very readily; the glands themselves becoming coated with
the thinnest layer of metallic gold, and particles float about on the
surface of the surrounding fluid.

Lead, Chloride of.—Three leaves were immersed in ninety minims of a
solution of one part to 437 of water. After 23 hrs. there was not a
trace of inflection; the glands were not blackened, and the leaves did
not appear injured. They were then trans- [page 185] ferred to the
solution (1 gr. to 20 oz.) of phosphate of ammonia, and after 24 hrs.
two of them were somewhat, the third very little, inflected; and they
thus remained for another 24 hrs.

Tin, Chloride of.—Four leaves were immersed in 120 minims of a solution
of about one part (all not being dissolved) to 437 of water. After 4
hrs. no effect; after 6 hrs. 30 m. all four leaves had their
submarginal tentacles inflected; after 22 hrs. every single tentacle
and the blades were closely inflected. The surrounding fluid was now
coloured pink. The leaves were washed and transferred to water, but
next morning were evidently dead. This chloride is a deadly poison, but
acts slowly.

Antimony, Tartrate of.—Three leaves were immersed in ninety minims of a
solution of one part to 437 of water. After 8 hrs. 30 m. there was
slight inflection; after 24 hrs. two of the leaves were closely, and
the third moderately, inflected; glands not much darkened. The leaves
were washed and placed in water, but they remained in the same state
for 48 additional hours. This salt is probably poisonous, but acts
slowly.

Arsenious Acid.—A solution of one part to 437 of water; three leaves
were immersed in ninety minims; in 25 m. considerable inflection; in 1
h. great inflection; glands not discoloured. After 6 hrs. the leaves
were transferred to water; next morning they looked fresh, but after
four days were pale-coloured, had not re-expanded, and were evidently
dead.

Iron, Chloride of.—Three leaves were immersed in ninety minims of a
solution of one part to 437 of water; in 8 hrs. no inflection; but
after 24 hrs. considerable inflection; glands blackened; fluid coloured
yellow, with floating flocculent particles of oxide of iron. The leaves
were then placed in water; after 48 hrs. they had re-expanded a very
little, but I think were killed; glands excessively black.

Chromic Acid.—One part to 437 of water; three leaves were immersed in
ninety minims; in 30 m. some, and in 1 hr. considerable, inflection;
after 2 hrs. all the tentacles closely inflected, with the glands
discoloured. Placed in water, next day leaves quite discoloured and
evidently killed.

Manganese, Chloride of.—Three leaves immersed in ninety minims of a
solution of one part to 437 of water; after 22 hrs. no more inflection
than often occurs in water; glands not blackened. The leaves were then
placed in the usual solution of phosphate of ammonia, but no inflection
was caused even after 48 hrs.

Copper, Chloride of.—Three leaves immersed in ninety minims [page 186]
of a solution of one part to 437 of water; after 2 hrs. some
inflection; after 3 hrs. 45 m. tentacles closely inflected, with the
glands blackened. After 22 hrs. still closely inflected, and the leaves
flaccid. Placed in pure water, next day evidently dead. A rapid poison.

Nickel, Chloride of.—Three leaves immersed in ninety minims of a
solution of one part to 437 of water; in 25 m. considerable inflection,
and in 3 hrs. all the tentacles closely inflected. After 22 hrs. still
closely inflected; most of the glands, but not all, blackened. The
leaves were then placed in water; after 24 hrs. remained inflected;
were somewhat discoloured, with the glands and tentacles dingy red.
Probably killed.

Cobalt, Chloride of.—Three leaves immersed in ninety minims of a
solution of one part to 437 of water; after 23 hrs. there was not a
trace of inflection, and the glands were not more blackened than often
occurs after an equally long immersion in water.

Platinum, Chloride of.—Three leaves immersed in ninety minims of a
solution of one part to 437 of water; in 6 m. some inflection, which
became immense after 48 m. After 3 hrs. the glands were rather pale.
After 24 hrs. all the tentacles still closely inflected; glands
colourless; remained in same state for four days; leaves evidently
killed.]

Concluding Remarks on the Action of the foregoing Salts.—Of the
fifty-one salts and metallic acids which were tried, twenty-five caused
the tentacles to be inflected, and twenty-six had no such effect, two
rather doubtful cases occurring in each series. In the table at the
head of this discussion, the salts are arranged according to their
chemical affinities; but their action on Drosera does not seem to be
thus governed. The nature of the base is far more important, as far as
can be judged from the few experiments here given, than that of the
acid; and this is the conclusion at which physiologists have arrived
with respect to animals. We see this fact illustrated in all the nine
salts of soda causing inflection, and in not being poisonous except
when given in large doses; whereas seven of [page 187] the
corresponding salts of potash do not cause inflection, and some of them
are poisonous. Two of them, however, viz. the oxalate and iodide of
potash, slowly induced a slight and rather doubtful amount of
inflection. This difference between the two series is interesting, as
Dr. Burdon Sanderson informs me that sodium salts may be introduced in
large doses into the circulation of mammals without any injurious
effects; whilst small doses of potassium salts cause death by suddenly
arresting the movements of the heart. An excellent instance of the
different action of the two series is presented by the phosphate of
soda quickly causing vigorous inflection, whilst phosphate of potash is
quite inefficient. The great power of the former is probably due to the
presence of phosphorus, as in the cases of phosphate of lime and of
ammonia. Hence we may infer that Drosera cannot obtain phosphorus from
the phosphate of potash. This is remarkable, as I hear from Dr. Burdon
Sanderson that phosphate of potash is certainly decomposed within the
bodies of animals. Most of the salts of soda act very rapidly; the
iodide acting slowest. The oxalate, nitrate, and citrate seem to have a
special tendency to cause the blade of the leaf to be inflected. The
glands of the disc, after absorbing the citrate, transmit hardly any
motor impulse to the outer tentacles; and in this character the citrate
of soda resembles the citrate of ammonia, or a decoction of
grass-leaves; these three fluids all acting chiefly on the blade.

It seems opposed to the rule of the preponderant influence of the base
that the nitrate of lithium causes moderately rapid inflection, whereas
the acetate causes none; but this metal is closely allied to sodium
[page 188] and potassium,* which act so differently; therefore we might
expect that its action would be intermediate. We see, also, that
caesium causes inflection, and rubidium does not; and these two metals
are allied to sodium and potassium. Most of the earthy salts are
inoperative. Two salts of calcium, four of magnesium, two of barium,
and two of strontium, did not cause any inflection, and thus follow the
rule of the preponderant power of the base. Of three salts of
aluminium, one did not act, a second showed a trace of action, and the
third acted slowly and doubtfully, so that their effects are nearly
alike.

Of the salts and acids of ordinary metals, seventeen were tried, and
only four, namely those of zinc, lead, manganese, and cobalt, failed to
cause inflection. The salts of cadmium, tin, antimony, and iron, act
slowly; and the three latter seem more or less poisonous. The salts of
silver, mercury, gold, copper, nickel, and platinum, chromic and
arsenious acids, cause great inflection with extreme quickness, and are
deadly poisons. It is surprising, judging from animals, that lead and
barium should not be poisonous. Most of the poisonous salts make the
glands black, but chloride of platinum made them very pale. I shall
have occasion, in the next chapter, to add a few remarks on the
different effects of phosphate of ammonia on leaves previously immersed
in various solutions.

ACIDS.


I will first give, as in the case of the salts, a list of the
twenty-four acids which were tried, divided into two series, according
as they cause or do not cause

* Miller’s ‘Elements of Chemistry,’ 3rd edit. pp. 337, 448. [page 189]


inflection. After describing the experiments, a few concluding remarks
will be added.

ACIDS, MUCH DILUTED, WHICH CAUSE INFLECTION.


1. Nitric, strong inflection; poisonous. 2. Hydrochloric, moderate and
slow inflection; not poisonous. 3. Hydriodic, strong inflection;
poisonous. 4. Iodic, strong inflection; poisonous. 5. Sulphuric, strong
inflection; somewhat poisonous. 6. Phosphoric, strong inflection;
poisonous. 7. Boracic; moderate and rather slow inflection; not
poisonous. 8. Formic, very slight inflection; not poisonous. 9. Acetic,
strong and rapid inflection; poisonous. 10. Propionic, strong but not
very rapid inflection; poisonous. 11. Oleic, quick inflection; very
poisonous. 12. Carbolic, very slow inflection; poisonous. 13. Lactic,
slow and moderate inflection; poisonous. 14. Oxalic, moderately quick
inflection; very poisonous. 15. Malic, very slow but considerable
inflection; not poisonous. 16. Benzoic, rapid inflection; very
poisonous. 17. Succinic, moderately quick inflection: moderately
poisonous. 18. Hippuric, rather slow inflection; poisonous. 19.
Hydrocyanic, rather rapid inflection; very poisonous.

ACIDS, DILUTED TO THE SAME DEGREE, WHICH DO NOT CAUSE INFLECTION.


1. Gallic; not poisonous. 2. Tannic; not poisonous. 3. Tartaric; not
poisonous. 4. Citric; not poisonous. 5. Uric; (?) not poisonous.

Nitric Acid.—Four leaves were placed, each in thirty minims of one part
by weight of the acid to 437 of water, so that each received 1/16 of a
grain, or 4.048 mg. This strength was chosen for this and most of the
following experiments, as it is the same [page 190] as that of most of
the foregoing saline solutions. In 2 hrs. 30 m. some of the leaves were
considerably, and in 6 hrs. 30 m. all were immensely, inflected, as
were their blades. The surrounding fluid was slightly coloured pink,
which always shows that the leaves have been injured. They were then
left in water for three days; but they remained inflected and were
evidently killed. Most of the glands had become colourless. Two leaves
were then immersed, each in thirty minims of one part to 1000 of water;
in a few hours there was some inflection; and after 24 hrs. both leaves
had almost all their tentacles and blades inflected; they were left in
water for three days, and one partially re-expanded and recovered. Two
leaves were next immersed, each in thirty minims of one part to 2000 of
water; this produced very little effect, except that most of the
tentacles close to the summit of the petiole were inflected, as if the
acid had been absorbed by the cut-off end.

Hydrochloric Acid.—One part to 437 of water; four leaves were immersed
as before, each in thirty minims. After 6 hrs. only one leaf was
considerably inflected. After 8 hrs. 15 m. one had its tentacles and
blade well inflected; the other three were moderately inflected, and
the blade of one slightly. The surrounding fluid was not coloured at
all pink. After 25 hrs. three of these four leaves began to re-expand,
but their glands were of a pink instead of a red colour; after two more
days they fully re-expanded; but the fourth leaf remained inflected,
and seemed much injured or killed, with its glands white. Four leaves
were then treated, each with thirty minims of one part to 875 of water;
after 21 hrs. they were moderately inflected; and on being transferred
to water, fully re-expanded in two days, and seemed quite healthy.

Hydriodic Acid.—One to 437 of water; three leaves were immersed as
before, each in thirty minims. After 45 m. the glands were discoloured,
and the surrounding fluid became pinkish, but there was no inflection.
After 5 hrs. all the tentacles were closely inflected; and an immense
amount of mucus was secreted, so that the fluid could be drawn out into
long ropes. The leaves were then placed in water, but never
re-expanded, and were evidently killed. Four leaves were next immersed
in one part to 875 of water; the action was now slower, but after 22
hrs. all four leaves were closely inflected, and were affected in other
respects as above described. These leaves did not re-expand, though
left for four days in water. This acid acts far more powerfully than
hydrochloric, and is poisonous.

Iodic Acid.—One to 437 of water; three leaves were immersed, [page 191]
each in thirty minims; after 3 hrs. strong inflection; after 4 hrs.
glands dark brown; after 8 hrs. 30 m. close inflection, and the leaves
had become flaccid; surrounding fluid not coloured pink. These leaves
were then placed in water, and next day were evidently dead.

Sulphuric Acid.—One to 437 of water; four leaves were immersed, each in
thirty minims; after 4 hrs. great inflection; after 6 hrs. surrounding
fluid just tinged pink; they were then placed in water, and after 46
hrs. two of them were still closely inflected, two beginning to
re-expand; many of the glands colourless. This acid is not so poisonous
as hydriodic or iodic acids.

Phosphoric Acid.—One to 437 of water; three leaves were immersed
together in ninety minims; after 5 hrs. 30 m. some inflection, and some
glands colourless; after 8 hrs. all the tentacles closely inflected,
and many glands colourless; surrounding fluid pink. Left in water for
two days and a half, remained in the same state and appeared dead.

Boracic Acid.—One to 437 of water; four leaves were immersed together
in 120 minims; after 6 hrs. very slight inflection; after 8 hrs. 15 m.
two were considerably inflected, the other two slightly. After 24 hrs.
one leaf was rather closely inflected, the second less closely, the
third and fourth moderately. The leaves were washed and put into water;
after 24 hrs. they were almost fully re-expanded and looked healthy.
This acid agrees closely with hydrochloric acid of the same strength in
its power of causing inflection, and in not being poisonous.

Formic Acid.—Four leaves were immersed together in 120 minims of one
part to 437 of water; after 40 m. slight, and after 6 hrs. 30 m. very
moderate inflection; after 22 hrs. only a little more inflection than
often occurs in water. Two of the leaves were then washed and placed in
a solution (1 gr. to 20 oz.) of phosphate of ammonia; after 24 hrs.
they were considerably inflected, with the contents of their cells
aggregated, showing that the phosphate had acted, though not to the
full and ordinary degree.

Acetic Acid.—Four leaves were immersed together in 120 minims of one
part to 437 of water. In 1 hr. 20 m. the tentacles of all four and the
blades of two were greatly inflected. After 8 hrs. the leaves had
become flaccid, but still remained closely inflected, the surrounding
fluid being coloured pink. They were then washed and placed in water;
next morning they were still inflected and of a very dark red colour,
but with their glands colourless. After another day they were
dingy-coloured, and [page 192] evidently dead. This acid is far more
powerful than formic, and is highly poisonous. Half-minim drops of a
stronger mixture (viz. one part by measure to 320 of water) were placed
on the discs of five leaves; none of the exterior tentacles, only those
on the borders of the disc which actually absorbed the acid, became
inflected. Probably the dose was too strong and paralysed the leaves,
for drops of a weaker mixture caused much inflection; nevertheless the
leaves all died after two days.

Propionic Acid.—Three leaves were immersed in ninety minims of a
mixture of one part to 437 of water; in 1 hr. 50 m. there was no
inflection; but after 3 hrs. 40 m. one leaf was greatly inflected, and
the other two slightly. The inflection continued to increase, so that
in 8 hrs. all three leaves were closely inflected. Next morning, after
20 hrs., most of the glands were very pale, but some few were almost
black. No mucus had been secreted, and the surrounding fluid was only
just perceptibly tinted of a pale pink. After 46 hrs. the leaves became
slightly flaccid and were evidently killed, as was afterwards proved to
be the case by keeping them in water. The protoplasm in the closely
inflected tentacles was not in the least aggregated, but towards their
bases it was collected in little brownish masses at the bottoms of the
cells. This protoplasm was dead, for on leaving the leaf in a solution
of carbonate of ammonia, no aggregation ensued. Propionic acid is
highly poisonous to Drosera, like its ally acetic acid, but induces
inflection at a much slower rate.

Oleic Acid (given me by Prof. Frankland).—Three leaves were immersed in
this acid; some inflection was almost immediately caused, which
increased slightly, but then ceased, and the leaves seemed killed. Next
morning they were rather shrivelled, and many of the glands had fallen
off the tentacles. Drops of this acid were placed on the discs of four
leaves; in 40 m. all the tentacles were greatly inflected, excepting
the extreme marginal ones; and many of these after 3 hrs. became
inflected. I was led to try this acid from supposing that it was
present (which does not seem to be the case)* in olive oil, the action
of which is anomalous. Thus drops of this oil placed on the disc do not
cause the outer tentacles to be inflected; yet when minute drops were
added to the secretion surrounding the glands of the outer tentacles,
these were occasionally, but by no means always, inflected. Two leaves
were also immersed in this oil, and there

* See articles on Glycerine and Oleic Acid in Watts’ ‘Dict. of
Chemistry.’ [page 193]


was no inflection for about 12 hrs.; but after 23 hrs. almost all the
tentacles were inflected. Three leaves were likewise immersed in
unboiled linseed oil, and soon became somewhat, and in 3 hrs. greatly,
inflected. After 1 hr. the secretion round the glands was coloured
pink. I infer from this latter fact that the power of linseed oil to
cause inflection cannot be attributed to the albumin which it is said
to contain.

Carbolic Acid.—Two leaves were immersed in sixty minims of a solution
of 1 gr. to 437 of water; in 7 hrs. one was slightly, and in 24 hrs.
both were closely, inflected, with a surprising amount of mucus
secreted. These leaves were washed and left for two days in water; they
remained inflected; most of their glands became pale, and they seemed
dead. This acid is poisonous, but does not act nearly so rapidly or
powerfully as might have been expected from its known destructive power
on the lowest organisms. Half-minims of the same solution were placed
on the discs of three leaves; after 24 hrs. no inflection of the outer
tentacles ensued, and when bits of meat were given them, they became
fairly well inflected. Again half-minims of a stronger solution, of one
part to 218 of water, were placed on the discs of three leaves; no
inflection of the outer tentacles ensued; bits of meat were then given
as before; one leaf alone became well inflected, the discal glands of
the other two appearing much injured and dry. We thus see that the
glands of the discs, after absorbing this acid, rarely transmit any
motor impulse to the outer tentacles; though these, when their own
glands absorb the acid, are strongly acted on.

Lactic Acid.—Three leaves were immersed in ninety minims of one part to
437 of water. After 48 m. there was no inflection, but the surrounding
fluid was coloured pink; after 8 hrs. 30 m. one leaf alone was a little
inflected, and almost all the glands on all three leaves were of a very
pale colour. The leaves were then washed and placed in a solution (1
gr. to 20 oz.) of phosphate of ammonia; after about 16 hrs. there was
only a trace of inflection. They were left in the phosphate for 48
hrs., and remained in the same state, with almost all their glands
discoloured. The protoplasm within the cells was not aggregated, except
in a very few tentacles, the glands of which were not much discoloured.
I believe, therefore, that almost all the glands and tentacles had been
killed by the acid so suddenly that hardly any inflection was caused.
Four leaves were next immersed in 120 minims of a weaker solution, of
one part to 875 of water; after 2 hrs. 30 m. the surrounding fluid was
quite pink; the glands were pale, but [page 194] there was no
inflection; after 7 hrs. 30 m. two of the leaves showed some
inflection, and the glands were almost white; after 21 hrs. two of the
leaves were considerably inflected, and a third slightly; most of the
glands were white, the others dark red. After 45 hrs. one leaf had
almost every tentacle inflected; a second a large number; the third and
fourth very few; almost all the glands were white, excepting those on
the discs of two of the leaves, and many of these were very dark red.
The leaves appeared dead. Hence lactic acid acts in a very peculiar
manner, causing inflection at an extraordinarily slow rate, and being
highly poisonous. Immersion in even weaker solutions, viz. of one part
to 1312 and 1750 of water, apparently killed the leaves (the tentacles
after a time being bowed backwards), and rendered the glands white, but
caused no inflection.

Gallic, Tannic, Tartaric, and Citric Acids.—One part to 437 of water.
Three or four leaves were immersed, each in thirty minims of these four
solutions, so that each leaf received 1/16 of a grain, or 4.048 mg. No
inflection was caused in 24 hrs., and the leaves did not appear at all
injured. Those which had been in the tannic and tartaric acids were
placed in a solution (1 gr. to 20 oz.) of phosphate of ammonia, but no
inflection ensued in 24 hrs. On the other hand, the four leaves which
had been in the citric acid, when treated with the phosphate, became
decidedly inflected in 50 m. and strongly inflected after 5 hrs., and
so remained for the next 24 hrs.

Malic Acid.—Three leaves were immersed in ninety minims of a solution
of one part to 437 of water; no inflection was caused in 8 hrs. 20 m.,
but after 24 hrs. two of them were considerably, and the third
slightly, inflected—more so than could be accounted for by the action
of water. No great amount of mucus was secreted. They were then placed
in water, and after two days partially re-expanded. Hence this acid is
not poisonous.

Oxalic Acid.—Three leaves were immersed in ninety minims of a solution
of 1 gr. to 437 of water; after 2 hrs. 10 m. there was much inflection;
glands pale; the surrounding fluid of a dark pink colour; after 8 hrs.
excessive inflection. The leaves were then placed in water; after about
16 hrs. the tentacles were of a very dark red colour, like those of the
leaves in acetic acid. After 24 additional hours, the three leaves were
dead and their glands colourless.

Benzoic Acid.—Five leaves were immersed, each in thirty minims of a
solution of 1 gr. to 437 of water. This solution was so weak that it
only just tasted acid, yet, as we shall see, was highly poisonous to
Drosera. After 52 m. the submarginal [page 195] tentacles were somewhat
inflected, and all the glands very pale-coloured; the surrounding fluid
was coloured pink. On one occasion the fluid became pink in the course
of only 12 m., and the glands as white as if the leaf had been dipped
in boiling water. After 4 hrs. much inflection; but none of the
tentacles were closely inflected, owing, as I believe, to their having
been paralysed before they had time to complete their movement. An
extraordinary quantity of mucus was secreted. Some of the leaves were
left in the solution; others, after an immersion of 6 hrs. 30 m., were
placed in water. Next morning both lots were quite dead; the leaves in
the solution being flaccid, those in the water (now coloured yellow) of
a pale brown tint, and their glands white.

Succinic Acid.—Three leaves were immersed in ninety minims of a
solution of 1 gr. to 437 of water; after 4 hrs. 15 m. considerable and
after 23 hrs. great inflection; many of the glands pale; fluid coloured
pink. The leaves were then washed and placed in water; after two days
there was some re-expansion, but many of the glands were still white.
This acid is not nearly so poisonous as oxalic or benzoic.

Uric Acid.—Three leaves were immersed in 180 minims of a solution of 1
gr. to 875 of warm water, but all the acid was not dissolved; so that
each received nearly 1/16 of a grain. After 25 m. there was some slight
inflection, but this never increased; after 9 hrs. the glands were not
discoloured, nor was the solution coloured pink; nevertheless much
mucus was secreted. The leaves were then placed in water, and by next
morning fully re-expanded. I doubt whether this acid really causes
inflection, for the slight movement which at first occurred may have
been due to the presence of a trace of albuminous matter. But it
produces some effect, as shown by the secretion of so much mucus.

Hippuric Acid.—Four leaves were immersed in 120 minims of a solution of
1 gr. to 437 of water. After 2 hrs. the fluid was coloured pink; glands
pale, but no inflection. After 6 hrs. some inflection; after 9 hrs. all
four leaves greatly inflected; much mucus secreted; all the glands very
pale. The leaves were then left in water for two days; they remained
closely inflected, with their glands colourless, and I do not doubt
were killed.

Hydrocyanic Acid.—Four leaves were immersed, each in thirty minims of
one part to 437 of water; in 2 hrs. 45 m. all the tentacles were
considerably inflected, with many of the glands pale; after 3 hrs. 45
m. all strongly inflected, and the surrounding fluid coloured pink;
after 6 hrs. all closely inflected. After [page 196] an immersion of 8
hrs. 20 m. the leaves were washed and placed in water; next morning,
after about 16 hrs., they were still inflected and discoloured; on the
succeeding day they were evidently dead. Two leaves were immersed in a
stronger mixture, of one part to fifty of water; in 1 hr. 15 m. the
glands became as white as porcelain, as if they had been dipped in
boiling water; very few of the tentacles were inflected; but after 4
hrs. almost all were inflected. These leaves were then placed in water,
and next morning were evidently dead. Half-minim drops of the same
strength (viz. one part to fifty of water) were next placed on the
discs of five leaves; after 21 hrs. all the outer tentacles were
inflected, and the leaves appeared much injured. I likewise touched the
secretion round a large number of glands with minute drops (about 1/20
of a minim, or .00296 ml.) of Scheele’s mixture (6 per cent.); the
glands first became bright red, and after 3 hrs. 15 m. about two-thirds
of the tentacles bearing these glands were inflected, and remained so
for the two succeeding days, when they appeared dead.]

Concluding Remarks on the Action of Acids.—It is evident that acids
have a strong tendency to cause the inflection of the tentacles;* for
out of the twenty-four acids tried, nineteen thus acted, either rapidly
and energetically, or slowly and slightly. This fact is remarkable, as
the juices of many plants contain more acid, judging by the taste, than
the solutions employed in my experiments. From the powerful effects of
so many acids on Drosera, we are led to infer that those naturally
contained in the tissues of this plant, as well as of others, must play
some important part in their economy. Of the five cases in which acids
did not cause the tentacles to be inflected, one is doubtful; for uric
acid did act slightly, and caused a copious secretion of mucus. Mere
sourness to the taste is no

* According to M. Fournier (‘De la Fcondation dans les Phanrogames.’
1863, p. 61) drops of acetic, hydrocyanic, and sulphuric acid cause the
stamens of Berberis instantly to close; though drops of water have no
such power, which latter statement I can confirm; [page 197]


criterion of the power of an acid on Drosera, as citric and tartaric
acids are very sour, yet do not excite inflection. It is remarkable how
acids differ in their power. Thus, hydrochloric acid acts far less
powerfully than hydriodic and many other acids of the same strength,
and is not poisonous. This is an interesting fact, as hydrochloric acid
plays so important a part in the digestive process of animals. Formic
acid induces very slight inflection, and is not poisonous; whereas its
ally, acetic acid, acts rapidly and powerfully, and is poisonous. Malic
acid acts slightly, whereas citric and tartaric acids produce no
effect. Lactic acid is poisonous, and is remarkable from inducing
inflection only after a considerable interval of time. Nothing
surprised me more than that a solution of benzoic acid, so weak as to
be hardly acidulous to the taste, should act with great rapidity and be
highly poisonous; for I am informed that it produces no marked effect
on the animal economy. It may be seen, by looking down the list at the
head of this discussion, that most of the acids are poisonous, often
highly so. Diluted acids are known to induce negative osmose,* and the
poisonous action of so many acids on Drosera is, perhaps, connected
with this power, for we have seen that the fluids in which they were
immersed often became pink, and the glands pale-coloured or white. Many
of the poisonous acids, such as hydriodic, benzoic, hippuric, and
carbolic (but I neglected to record all the cases), caused the
secretion of an extraordinary amount of mucus, so that long ropes of
this matter hung from the leaves when they were lifted out of the
solutions. Other acids, such as hydrochloric and malic, have no such
ten-

* Miller’s ‘Elements of Chemistry,’ part i. 1867, p. 87. [page 198]


dency; in these two latter cases the surrounding fluid was not coloured
pink, and the leaves were not poisoned. On the other hand, propionic
acid, which is poisonous, does not cause much mucus to be secreted, yet
the surrounding fluid became slightly pink. Lastly, as in the case of
saline solutions, leaves, after being immersed in certain acids, were
soon acted on by phosphate of ammonia; on the other hand, they were not
thus affected after immersion in certain other acids. To this subject,
however, I shall have to recur. [page 199]




CHAPTER IX.
THE EFFECTS OF CERTAIN ALKALOID POISONS, OTHER SUBSTANCES AND VAPOURS.


Strychnine, salts of—Quinine, sulphate of, does not soon arrest the
movement of the protoplasm—Other salts of
quinine—Digitaline—Nicotine—Atropine—Veratrine— Colchicine—
Theine—Curare—Morphia—Hyoscyamus—Poison of the cobra, apparently
accelerates the movements of the protoplasm—Camphor, a powerful
stimulant, its vapour narcotic—Certain essential oils excite
movement—Glycerine—Water and certain solutions retard or prevent the
subsequent action of phosphate of ammonia—Alcohol innocuous, its vapour
narcotic and poisonous—Chloroform, sulphuric and nitric ether, their
stimulant, poisonous, and narcotic power—Carbonic acid narcotic, not
quickly poisonous—Concluding remarks.


As in the last chapter, I will first give my experiments, and then a
brief summary of the results with some concluding remarks.

[Acetate of Strychnine.—Half-minims of a solution of one part to 437 of
water were placed on the discs of six leaves; so that each received
1/960 of a grain, or .0675 mg. In 2 hrs. 30 m. the outer tentacles on
some of them were inflected, but in an irregular manner, sometimes only
on one side of the leaf. The next morning, after 22 hrs. 30 m. the
inflection had not increased. The glands on the central disc were
blackened, and had ceased secreting. After an additional 24 hrs. all
the central glands seemed dead, but the inflected tentacles had
re-expanded and appeared quite healthy. Hence the poisonous action of
strychnine seems confined to the glands which have absorbed it;
nevertheless, these glands transmit a motor impulse to the exterior
tentacles. Minute drops (about 1/20 of a minim) of the same solution
applied to the glands of the outer tentacles occasionally caused them
to bend. The poison does not seem to act quickly, for having applied to
several glands similar drops of a rather stronger solution, of one part
to 292 of water, this did not prevent the tentacles bending, when their
glands [page 200] were excited, after an interval of a quarter to three
quarters of an hour, by being rubbed or given bits of meat. Similar
drops of a solution of one part to 218 of water (2 grs. to 1 oz.)
quickly blackened the glands; some few tentacles thus treated moved,
whilst others did not. The latter, however, on being subsequently
moistened with saliva or given bits of meat, became incurved, though
with extreme slowness; and this shows that they had been injured.
Stronger solutions (but the strength was not ascertained) sometimes
arrested all power of movement very quickly; thus bits of meat were
placed on the glands of several exterior tentacles, and as soon as they
began to move, minute drops of the strong solution were added. They
continued for a short time to go on bending, and then suddenly stood
still; other tentacles on the same leaves, with meat on their glands,
but not wetted with the strychnine, continued to bend and soon reached
the centre of the leaf.

Citrate of Strychnine.—Half-minims of a solution of one part to 437 of
water were placed on the discs of six leaves; after 24 hrs. the outer
tentacles showed only a trace of inflection. Bits of meat were then
placed on three of these leaves, but in 24 hrs. only slight and
irregular inflection occurred, proving that the leaves had been greatly
injured. Two of the leaves to which meat had not been given had their
discal glands dry and much injured. Minute drops of a strong solution
of one part to 109 of water (4 grs. to 1 oz.) were added to the
secretion round several glands, but did not produce nearly so plain an
effect as the drops of a much weaker solution of the acetate. Particles
of the dry citrate were placed on six glands; two of these moved some
way towards the centre, and then stood still, being no doubt killed;
three others curved much farther inwards, and were then fixed; one
alone reached the centre. Five leaves were immersed, each in thirty
minims of a solution of one part to 437 of water; so that each received
1/16 of a grain; after about 1 hr. some of the outer tentacles became
inflected, and the glands were oddly mottled with black and white.
These glands, in from 4 hrs. to 5 hrs., became whitish and opaque, and
the protoplasm in the cells of the tentacles was well aggregated. By
this time two of the leaves were greatly inflected, but the three
others not much more inflected than they were before. Nevertheless two
fresh leaves, after an immersion respectively for 2 hrs. and 4 hrs. in
the solution, were not killed; for on being left for 1 hr. 30 m. in a
solution of one part of carbonate of ammonia to 218 of water, their
tentacles became more inflected, and there was much aggregation. The
glands [page 201] of two other leaves, after an immersion for 2 hrs. in
a stronger solution, of one part of the citrate to 218 of water, became
of an opaque, pale pink colour, which before long disappeared, leaving
them white. One of these two leaves had its blade and tentacles greatly
inflected; the other hardly at all; but the protoplasm in the cells of
both was aggregated down to the bases of the tentacles, with the
spherical masses in the cells close beneath the glands blackened. After
24 hrs. one of these leaves was colourless, and evidently dead.

Sulphate of Quinine.—Some of this salt was added to water, which is
said to dissolve 1/1000 part of its weight. Five leaves were immersed,
each in thirty minims of this solution, which tasted bitter. In less
than 1 hr. some of them had a few tentacles inflected. In 3 hrs. most
of the glands became whitish, others dark-coloured, and many oddly
mottled. After 6 hrs. two of the leaves had a good many tentacles
inflected, but this very moderate degree of inflection never increased.
One of the leaves was taken out of the solution after 4 hrs., and
placed in water; by the next morning some few of the inflected
tentacles had re-expanded, showing that they were not dead; but the
glands were still much discoloured. Another leaf not included in the
above lot, after an immersion of 3 hrs. 15 m., was carefully examined;
the protoplasm in the cells of the outer tentacles, and of the short
green ones on the disc, had become strongly aggregated down to their
bases; and I distinctly saw that the little masses changed their
positions and shapes rather rapidly; some coalescing and again
separating. I was surprised at this fact, because quinine is said to
arrest all movement in the white corpuscles of the blood; but as,
according to Binz,* this is due to their being no longer supplied with
oxygen by the red corpuscles, any such arrestment of movement could not
be expected in Drosera. That the glands had absorbed some of the salt
was evident from their change of colour; but I at first thought that
the solution might not have travelled down the cells of the tentacles,
where the protoplasm was seen in active movement. This view, however, I
have no doubt, is erroneous, for a leaf which had been immersed for 3
hrs. in the quinine solution was then placed in a little solution of
one part of carbonate of ammonia to 218 of water; and in 30 m. the
glands and the upper cells of the tentacles became intensely black,
with the protoplasm presenting a very unusual appearance; for it

* ‘Quarterly Journal of Microscopical Science,’ April 1874, p. 185.
[page 202]


had become aggregated into reticulated dingy-coloured masses, having
rounded and angular interspaces. As I have never seen this effect
produced by the carbonate of ammonia alone, it must be attributed to
the previous action of the quinine. These reticulated masses were
watched for some time, but did not change their forms; so that the
protoplasm no doubt had been killed by the combined action of the two
salts, though exposed to them for only a short time.

Another leaf, after an immersion for 24 hrs. in the quinine solution,
became somewhat flaccid, and the protoplasm in all the cells was
aggregated. Many of the aggregated masses were discoloured, and
presented a granular appearance; they were spherical, or elongated, or
still more commonly consisted of little curved chains of small
globules. None of these masses exhibited the least movement, and no
doubt were all dead.

Half-minims of the solution were placed on the discs of six leaves;
after 23 hrs. one had all its tentacles, two had a few, and the others
none inflected; so that the discal glands, when irritated by this salt,
do not transmit any strong motor impulse to the outer tentacles. After
48 hrs. the glands on the discs of all six leaves were evidently much
injured or quite killed. It is clear that this salt is highly
poisonous.*

Acetate of Quinine.—Four leaves were immersed, each in thirty minims of
a solution of one part to 437 of water. The solution was tested with
litmus paper, and was not acid. After only 10 m. all four leaves were
greatly, and after 6 hrs. immensely, inflected. They were then left in
water for 60 hrs., but never re-expanded; the glands were white, and
the leaves evidently dead. This salt is far more efficient than the
sulphate in causing inflection, and, like that salt, is highly
poisonous.

Nitrate of Quinine.—Four leaves were immersed, each in thirty minims of
a solution of one part to 437 of water. After 6 hrs. there was hardly a
trace of inflection; after 22 hrs. three of the leaves were moderately,
and the fourth slightly inflected; so that this salt induces, though
rather slowly, well-marked inflection. These leaves, on being left in
water for 48 hrs., almost

*Binz found several years ago (as stated in ‘The Journal of Anatomy and
Phys.’ November 1872, p. 195) that quinia is an energetic poison to low
vegetable and animal organisms. Even one part added to 4000 parts of
blood arrests the movements of the white corpuscles, which become
“rounded and granular.” In the tentacles of Drosera the aggregated
masses of protoplasm, which appeared killed by the quinine, likewise
presented a granular appearance. A similar appearance is caused by very
hot water. [page 203]


completely re-expanded, but the glands were much discoloured. Hence
this salt is not poisonous in any high degree. The different action of
the three foregoing salts of quinine is singular.

Digitaline.—Half-minims of a solution of one part to 437 of water were
placed on the discs of five leaves. In 3 hrs. 45 m. Some of them had
their tentacles, and one had its blade, moderately inflected. After 8
hrs. three of them were well inflected; the fourth had only a few
tentacles inflected, and the fifth (an old leaf) was not at all
affected. They remained in nearly the same state for two days, but the
glands on their discs became pale. On the third day the leaves appeared
much injured. Nevertheless, when bits of meat were placed on two of
them, the outer tentacles became inflected. A minute drop (about 1/20
of a minim) of the solution was applied to three glands, and after 6
hrs. all three tentacles were inflected, but next day had nearly
re-expanded; so that this very small dose of 1/28800 of a grain (.00225
mg.) acts on a tentacle, but is not poisonous. It appears from these
several facts that digitaline causes inflection, and poisons the glands
which absorb a moderately large amount.

Nicotine.—The secretion round several glands was touched with a minute
drop of the pure fluid, and the glands were instantly blackened; the
tentacles becoming inflected in a few minutes. Two leaves were immersed
in a weak solution of two drops to 1 oz., or 437 grains, of water. When
examined after 3 hrs. 20 m., only twenty-one tentacles on one leaf were
closely inflected, and six on the other slightly so; but all the glands
were blackened, or very dark-coloured, with the protoplasm in all the
cells of all the tentacles much aggregated and dark-coloured. The
leaves were not quite killed, for on being placed in a little solution
of carbonate of ammonia (2 grs. to 1 oz.) a few more tentacles became
inflected, the remainder not being acted on during the next 24 hrs.

Half-minims of a stronger solution (two drops to 1/2 oz. of water) were
placed on the discs of six leaves, and in 30 m. all those tentacles
became inflected; the glands of which had actually touched the
solution, as shown by their blackness; but hardly any motor influence
was transmitted to the outer tentacles. After 22 hrs. most of the
glands on the discs appeared dead; but this could not have been the
case, as when bits of meat were placed on three of them, some few of
the outer tentacles were inflected in 24 hrs. Hence nicotine has a
great tendency to blacken the glands and to induce aggregation [page
204] of the protoplasm, but, except when pure, has very moderate power
of inducing inflection, and still less power of causing a motor
influence to be transmitted from the discal glands to the outer
tentacles. It is moderately poisonous.

Atropine.—A grain was added to 437 grains of water, but was not all
dissolved; another grain was added to 437 grains of a mixture of one
part of alcohol to seven parts of water; and a third solution was made
by adding one part of valerianate of atropine to 437 of water.
Half-minims of these three solutions were placed, in each case, on the
discs of six leaves; but no effect whatever was produced, excepting
that the glands on the discs to which the valerianate was given were
slightly discoloured. The six leaves on which drops of the solution of
atropine in diluted alcohol had been left for 21 hrs. were given bits
of meat, and all became in 24 hrs. fairly well inflected; so that
atropine does not excite movement, and is not poisonous. I also tried
in the same manner the alkaloid sold as daturine, which is believed not
to differ from atropine, and it produced no effect. Three of the leaves
on which drops of this latter solution had been left for 24 hrs. were
likewise given bits of meat, and they had in the course of 24 hrs. a
good many of their submarginal tentacles inflected.

Veratrine, Colchicine, Theine.—Solutions were made of these three
alkaloids by adding one part to 437 of water. Half-minims were placed,
in each case; on the discs of at least six leaves, but no inflection
was caused, except perhaps a very slight amount by the theine.
Half-minims of a strong infusion of tea likewise produced, as formerly
stated, no effect. I also tried similar drops of an infusion of one
part of the extract of colchicum, sold by druggists, to 218 of water;
and the leaves were observed for 48 hrs., without any effect being
produced. The seven leaves on which drops of veratrine had been left
for 26 hrs. were given bits of meat, and after 21 hrs. were well
inflected. These three alkaloids are therefore quite innocuous.

Curare.—One part of this famous poison was added to 218 of water, and
three leaves were immersed in ninety minims of the filtered solution.
In 3 hrs. 30 m. some of the tentacles were a little inflected; as was
the blade of one; after 4 hrs. After 7 hrs. the glands were wonderfully
blackened, showing that matter of some kind had been absorbed. In 9
hrs. two of the leaves had most of their tentacles sub-inflected, but
the inflection did not increase in the course of 24 hrs. One of these
leaves, after being immersed for 9 hrs. in the solution, was placed in
water, and by next morning had largely re-expanded; [page 205] the
other two, after their immersion for 24 hrs., were likewise placed in
water, and in 24 hrs. were considerably re-expanded, though their
glands were as black as ever. Half-minims were placed on the discs of
six leaves, and no inflection ensued; but after three days the glands
on the discs appeared rather dry, yet to my surprise were not
blackened. On another occasion drops were placed on the discs of six
leaves, and a considerable amount of inflection was soon caused; but as
I had not filtered the solution, floating particles may have acted on
the glands. After 24 hrs. bits of meat were placed on the discs of
three of these leaves, and next day they became strongly inflected. As
I at first thought that the poison might not have been dissolved in
pure water, one grain was added to 437 grains of a mixture of one part
of alcohol to seven of water, and half-minims were placed on the discs
of six leaves. These were not at all affected, and when after a day
bits of meat were given them, they were slightly inflected in 5 hrs.,
and closely after 24 hrs. It follows from these several facts that a
solution of curare induces a very moderate degree of inflection, and
this may perhaps be due to the presence of a minute quantity of
albumen. It certainly is not poisonous. The protoplasm in one of the
leaves, which had been immersed for 24 hrs., and which had become
slightly inflected, had undergone a very slight amount of
aggregation—not more than often ensues from an immersion of this length
of time in water.

Acetate of Morphia.—I tried a great number of experiments with this
substance, but with no certain result. A considerable number of leaves
were immersed from between 2 hrs. and 6 hrs. in a solution of one part
to 218 of water, and did not become inflected. Nor were they poisoned;
for when they were washed and placed in weak solutions of phosphate and
carbonate of ammonia, they soon became strongly inflected, with the
protoplasm in the cells well aggregated. If, however, whilst the leaves
were immersed in the morphia, phosphate of ammonia was added,
inflection did not rapidly ensue. Minute drops of the solution were
applied in the usual manner to the secretion round between thirty and
forty glands; and when, after an interval of 6 m:, bits of meat, a
little saliva, or particles of glass, were placed on them, the movement
of the tentacles was greatly retarded. But on other occasions no such
retardation occurred. Drops of water similarly applied never have any
retarding power. Minute drops of a solution of sugar of the same
strength (one part to 218 of water) sometimes retarded the subsequent
action of meat and of particles of glass, and [page 206] sometimes did
not do so. At one time I felt convinced that morphia acted as a
narcotic on Drosera, but after having found in what a singular manner
immersion in certain non-poisonous salts and acids prevents the
subsequent action of phosphate of ammonia, whereas other solutions have
no such power, my first conviction seems very doubtful.

Extract of Hyoscyamus.—Several leaves were placed, each in thirty
minims of an infusion of 3 grs. of the extract sold by druggists to 1
oz. of water. One of them, after being immersed for 5 hrs. 15 m., was
not inflected, and was then put into a solution (1 gr. to 1 oz.) of
carbonate of ammonia; after 2 hrs. 40 m. it was found considerably
inflected, and the glands much blackened. Four of the leaves, after
being immersed for 2 hrs. 14 m., were placed in 120 minims of a
solution (1 gr. to 20 oz.) of phosphate of ammonia; they had already
become slightly inflected from the hyoscyamus, probably owing to the
presence of some albuminous matter, as formerly explained, but the
inflection immediately increased, and after 1 hr. was strongly
pronounced; so that hyoscyamus does not act as a narcotic or poison.

Poison from the Fang of a Living Adder.—Minute drops were placed on the
glands of many tentacles; these were quickly inflected, just as if
saliva had been given them, Next morning, after 17 hrs. 30 m., all were
beginning to re-expand, and they appeared uninjured.

Poison from the Cobra.—Dr. Fayrer, well known from his investigations
on the poison of this deadly snake, was so kind as to give me some in a
dried state. It is an albuminous substance, and is believed to replace
the ptyaline of saliva.* A minute drop (about 1/20 of a minim) of a
solution of one part to 437 of water was applied to the secretion round
four glands; so that each received only about 1/38400 of a grain (.0016
mg.). The operation was repeated on four other glands; and in 15 m.
several of the eight tentacles became well inflected, and all of them
in 2 hrs. Next morning, after 24 hrs., they were still inflected, and
the glands of a very pale pink colour. After an additional 24 hrs. they
were nearly re-expanded, and completely so on the succeeding day; but
most of the glands remained almost white.

Half-minims of the same solution were placed on the discs of three
leaves, so that each received 1/960 of a grain (.0675 mg.); in

*Dr. Fayrer, ‘The Thanatophidia of India,’ 1872, p. 150. [page 207]


4 hrs. 15 m. the outer tentacles were much inflected; and after 6 hrs.
30 m. those on two of the leaves were closely inflected and the blade
of one; the third leaf was only moderately affected. The leaves
remained in the same state during the next day, but after 48 hrs.
re-expanded.

Three leaves were now immersed, each in thirty minims of the solution,
so that each received 1/16 of a grain, or 4.048 mg. In 6 m. there was
some inflection, which steadily increased, so that after 2 hrs. 30 m.
all three leaves were closely inflected; the glands were at first
somewhat darkened, then rendered pale; and the protoplasm within the
cells of the tentacles was partially aggregated. The little masses of
protoplasm were examined after 3 hrs., and again after 7 hrs., and on
no other occasion have I seen them undergoing such rapid changes of
form. After 8 hrs. 30 m. the glands had become quite white; they had
not secreted any great quantity of mucus. The leaves were now placed in
water, and after 40 hrs. re-expanded, showing that they were not much
or at all injured. During their immersion in water the protoplasm
within the cells of the tentacles was occasionally examined, and always
found in strong movement.

Two leaves were next immersed, each in thirty minims of a much stronger
solution, of one part to 109 of water; so that each received 1/4 of a
grain, or 16.2 mg; After 1 hr. 45 m. the sub-marginal tentacles were
strongly inflected, with the glands somewhat pale; after 3 hrs. 30 m.
both leaves had all their tentacles closely inflected and the glands
white. Hence the weaker solution, as in so many other cases, induced
more rapid inflection than the stronger one; but the glands were sooner
rendered white by the latter. After an immersion of 24 hrs. some of the
tentacles were examined, and the protoplasm, still of a fine purple
colour, was found aggregated into chains of small globular masses.
These changed their shapes with remarkable quickness. After an
immersion of 48 hrs. they were again examined, and their movements were
so plain that they could easily be seen under a weak power. The leaves
were now placed in water, and after 24 hrs. (i.e. 72 hrs. from their
first immersion) the little masses of protoplasm, which had become of a
dingy purple, were still in strong movement, changing their shapes,
coalescing, and again separating.

In 8 hrs. after these two leaves had been placed in water (i.e. in 56
hrs. after their immersion in the solution) they began to re-expand,
and by the next morning were more expanded. After an additional day
(i.e. on the fourth day after their immersion in the solution) they
were largely, but not quite fully [page 208] expanded. The tentacles
were now examined, and the aggregated masses were almost wholly
redissolved; the cells being filled with homogeneous purple fluid, with
the exception here and there of a single globular mass. We thus see how
completely the protoplasm had escaped all injury from the poison. As
the glands were soon rendered quite white, it occurred to me that their
texture might have been modified in such a manner as to prevent the
poison passing into the cells beneath, and consequently that the
protoplasm within these cells had not been at all affected. Accordingly
I placed another leaf, which had been immersed for 48 hrs. in the
poison and afterwards for 24 hrs. in water, in a little solution of one
part of carbonate of ammonia to 218 of water; in 30 m. the protoplasm
in the cells beneath the glands became darker, and in the course of 24
hrs. the tentacles were filled down to their bases with dark-coloured
spherical masses. Hence the glands had not lost their power of
absorption, as far as the carbonate of ammonia is concerned.

From these facts it is manifest that the poison of the cobra, though so
deadly to animals, is not at all poisonous to Drosera; yet it causes
strong and rapid inflection of the tentacles, and soon discharges all
colour from the glands. It seems even to act as a stimulant to the
protoplasm, for after considerable experience in observing the
movements of this substance in Drosera, I have never seen it on any
other occasion in so active a state. I was therefore anxious to learn
how this poison affected animal protoplasm; and Dr. Fayrer was so kind
as to make some observations for me, which he has since published.*
Ciliated epithelium from the mouth of a frog was placed in a solution
of .03 gramme to 4.6 cubic cm. of water; others being placed at the
same time in pure water for comparison. The movements of the cilia in
the solution seemed at first increased, but soon languished, and after
between 15 and 20 minutes ceased; whilst those in the water were still
acting vigorously. The white corpuscles of the blood of a frog, and the
cilia on two infusorial animals, a Paramaecium and Volvox, were
similarly affected by the poison. Dr. Fayrer also found that the muscle
of a frog lost its irritability after an immersion of 20 m. in the
solution, not then responding to a strong electrical current. On the
other hand, the movements of the cilia on the mantle of an Unio were
not always arrested, even when left for a consider-

* ‘Proceedings of Royal Society,’ Feb. 18, 1875. [page 209]


able time in a very strong solution. On the whole, it seems that the
poison of the cobra acts far more injuriously on the protoplasm of the
higher animals than on that of Drosera.

There is one other point which may be noticed. I have occasionally
observed that the drops of secretion round the glands were rendered
somewhat turbid by certain solutions, and more especially by some
acids, a film being formed on the surfaces of the drops; but I never
saw this effect produced in so conspicuous a manner as by the cobra
poison. When the stronger solution was employed, the drops appeared in
10 m. like little white rounded clouds. After 48 hrs. the secretion was
changed into threads and sheets of a membranous substance, including
minute granules of various sizes.

Camphor.—Some scraped camphor was left for a day in a bottle with
distilled water, and then filtered. A solution thus made is said to
contain 1/1000 of its weight of camphor; it smelt and tasted of this
substance. Ten leaves were immersed in this solution; after 15 m. five
of them were well inflected, two showing a first trace of movement in
11 m. and 12 m.; the sixth leaf did not begin to move until 15 m. had
elapsed, but was fairly well inflected in 17 m. and quite closed in 24
m.; the seventh began to move in 17 m., and was completely shut in 26
m. The eighth, ninth, and tenth leaves were old and of a very dark red
colour, and these were not inflected after an immersion of 24 hrs.; so
that in making experiments with camphor it is necessary to avoid such
leaves. Some of these leaves, on being left in the solution for 4 hrs.,
became of a rather dingy pink colour, and secreted much mucus; although
their tentacles were closely inflected, the protoplasm within the cells
was not at all aggregated. On another occasion, however, after a longer
immersion of 24 hrs., there was well marked aggregation. A solution
made by adding two drops of camphorated spirits to an ounce of water
did not act on one leaf; whereas thirty minims added to an ounce of
water acted on two leaves immersed together.

M. Vogel has shown* that the flowers of various plants do not wither so
soon when their stems are placed in a solution of camphor as when in
water; and that if already slightly withered, they recover more
quickly. The germination of certain seeds is also accelerated by the
solution. So that camphor acts as a stimulant, and it is the only known
stimulant for plants. I

* ‘Gardener’s Chronicle,’ 1874, p. 671. Nearly similar observations
were made in 1798 by B. S. Barton. [page 210]


wished, therefore, to ascertain whether camphor would render the leaves
of Drosera more sensitive to mechanical irritation than they naturally
are. Six leaves were left in distilled water for 5 m. or 6 m., and then
gently brushed twice or thrice, whilst still under water, with a soft
camel-hair brush; but no movement ensued. Nine leaves, which had been
immersed in the above solution of camphor for the times stated in the
following table, were next brushed only once with the same brush and in
the same manner as before; the results are given in the table. My first
trials were made by brushing the leaves whilst still immersed in the
solution; but it occurred to me that the viscid secretion round the
glands would thus be removed, and the camphor might act more
effectually on them. In all the following trials, therefore, each leaf
was taken out of the solution, waved for about 15 s. in water, then
placed in fresh water and brushed, so that the brushing would not allow
the freer access of the camphor; but this treatment made no difference
in the results.

Column 1 : Number of Leaves. Column 2 : Length of Immersion in the
Solution of Camphor. Column 3 : Length of Time between the Act of
Brushing and the Inflection of the Tentacles. Column 4 : Length of Time
between the Immersion of the Leaves in the Solution and the First Sign
of the Inflection of the Tentacles.

1 : 5 m. : 3 m. considerable inflection; 4 m. all the tentacles except
3 or 4 inflected. : 8 m.

2 : 5 m. : 6 m. first sign of inflection. : 11 m.

3 : 5 m. : 6 m. 30 s. slight inflection; 7 m. 30 s. plain inflection. :
11 m. 30 s.

4 : 4 m. 30 s. : 2 m. 30 s. a trace of inflection; 3 m. plain; 4 m.
strongly marked. : 7 m.

5 : 4 m. : 2 m. 30 s. a trace of inflection; 3 m. plain inflection. : 6
m. 30 s.

6 : 4 m. : 2 m. 30 s. decided inflection; 3 m. 30 s. strongly marked. :
6 m. 30 s.

7 : 4 m. : 2 m. 30 s. slight inflection; 3 m. plain; 4 m. well marked.
: 6 m. 30 s.

8 : 3 m. : 2 m. trace of inflection; 3 m. considerable, 6 m. strong
inflection. : 5 m.

9 : 3 m. : 2 m. trace of inflection; 3 m. considerable, 6 m. strong
inflection. : 5 m.

Other leaves were left in the solution without being brushed; one of
these first showed a trace of inflection after 11 m.; a second after 12
m.; five were not inflected until 15 m. had [page 211] elapsed, and two
not until a few minutes later. On the other hand, it will be seen in
the right-hand column of the table that most of the leaves subjected to
the solution, and which were brushed, became inflected in a much
shorter time. The movement of the tentacles of some of these leaves was
so rapid that it could be plainly seen through a very weak lens.

Two or three other experiments are worth giving. A large old leaf,
after being immersed for 10 m. in the solution, did not appear likely
to be soon inflected; so I brushed it, and in 2 m. it began to move,
and in 3 m. was completely shut. Another leaf, after an immersion of 15
m., showed no signs of inflection, so was brushed, and in 4 m. was
grandly inflected. A third leaf, after an immersion of 17 m., likewise
showed no signs of inflection; it was then brushed, but did not move
for 1 hr.; so that here was a failure. It was again brushed, and now in
9 m. a few tentacles became inflected; the failure therefore was not
complete.

We may conclude that a small dose of camphor in solution is a powerful
stimulant to Drosera. It not only soon excites the tentacles to bend,
but apparently renders the glands sensitive to a touch, which by itself
does not cause any movement. Or it may be that a slight mechanical
irritation not enough to cause any inflection yet gives some tendency
to movement, and thus reinforces the action of the camphor. This latter
view would have appeared to me the more probable one, had it not been
shown by M. Vogel that camphor is a stimulant in other ways to various
plants and seeds.

Two plants bearing four or five leaves, and with their roots in a
little cup of water, were exposed to the vapour of some bits of camphor
(about as large as a filbert-nut), under a vessel holding ten fluid oz.
After 10 hrs. no inflection ensued; but the glands appeared to be
secreting more copiously. The leaves were in a narcotised condition,
for on bits of meat being placed on two of them, there was no
inflection in 3 hrs. 15 m., and even after 13 hrs. 15 m. only a few of
the outer tentacles were slightly inflected; but this degree of
movement shows that the leaves had not been killed by an exposure
during 10 hrs. to the vapour of camphor.

Oil of Caraway.—Water is said to dissolve about a thousandth part of
its weight of this oil. A drop was added to an ounce of water and the
bottle occasionally shaken during a day; but many minute globules
remained undissolved. Five leaves were immersed in this mixture; in
from 4 m. to 5 m. there was some inflection, which became moderately
pronounced in two or [page 212] three additional minutes. After 14 m.
all five leaves were well, and some of them closely, inflected. After 6
hrs. the glands were white, and much mucus had been secreted. The
leaves were now flaccid, of a peculiar dull-red colour, and evidently
dead. One of the leaves, after an immersion of 4 m., was brushed, like
the leaves in the camphor, but this produced no effect. A plant with
its roots in water was exposed under a 10-oz. vessel to the vapour of
this oil, and in 1 hr. 20 m. one leaf showed a trace of inflection.
After 5 hrs. 20 m. the cover was taken off and the leaves examined; one
had all its tentacles closely inflected, the second about half in the
same state; and the third all sub-inflected. The plant was left in the
open air for 42 hrs., but not a single tentacle expanded; all the
glands appeared dead, except here and there one, which was still
secreting. It is evident that this oil is highly exciting and poisonous
to Drosera.

Oil of Cloves.—A mixture was made in the same manner as in the last
case, and three leaves were immersed in it. After 30 m. there was only
a trace of inflection which never increased. After 1 hr. 30 m. the
glands were pale, and after 6 hrs. white. No doubt the leaves were much
injured or killed.

Turpentine.—Small drops placed on the discs of some leaves killed them,
as did likewise drops of creosote. A plant was left for 15 m. under a
12-oz. vessel, with its inner surface wetted with twelve drops of
turpentine; but no movement of the tentacles ensued. After 24 hrs. the
plant was dead.

Glycerine.—Half-minims were placed on the discs of three leaves: in 2
hrs. some of the outer tentacles were irregularly inflected; and in 19
hrs. the leaves were flaccid and apparently dead; the glands which had
touched the glycerine were colourless. Minute drops (about 1/20 of a
minim) were applied to the glands of several tentacles, and in a few
minutes these moved and soon reached the centre. Similar drops of a
mixture of four dropped drops to 1 oz. of water were likewise applied
to several glands; but only a few of the tentacles moved, and these
very slowly and slightly. Half-minims of this same mixture placed on
the discs of some leaves caused, to my surprise, no inflection in the
course of 48 hrs. Bits of meat were then given them, and next day they
were well inflected; notwithstanding that some of the discal glands had
been rendered almost colourless. Two leaves were immersed in the same
mixture, but only for 4 hrs.; they were not inflected, and on being
afterwards left for 2 hrs. 30 m. in a solution (1 gr. to 1 oz.) of
carbonate of ammonia, their glands were blackened, their tentacles
inflected, and the protoplasm within their cells aggregated. It appears
[page 213] from these facts that a mixture of four drops of glycerine
to an ounce of water is not poisonous, and excites very little
inflection; but that pure glycerine is poisonous, and if applied in
very minute quantities to the glands of the outer tentacles causes
their inflection.

The Effects of Immersion in Water and in various Solutions on the
subsequent Action of Phosphate and Carbonate of Ammonia.—We have seen
in the third and seventh chapters that immersion in distilled water
causes after a time some degree of aggregation of the protoplasm, and a
moderate amount of inflection, especially in the case of plants which
have been kept at a rather high temperature. Water does not excite a
copious secretion of mucus. We have here to consider the effects of
immersion in various fluids on the subsequent action of salts of
ammonia and other stimulants. Four leaves which had been left for 24
hrs. in water were given bits of meat, but did not clasp them. Ten
leaves, after a similar immersion, were left for 24 hrs. in a powerful
solution (1 gr. to 20 oz.) of phosphate of ammonia, and only one showed
even a trace of inflection. Three of these leaves, on being left for an
additional day in the solution, still remained quite unaffected. When,
however, some of these leaves, which had been first immersed in water
for 24 hrs., and then in the phosphate for 24 hrs. were placed in a
solution of carbonate of ammonia (one part to 218 of water), the
protoplasm in the cells of the tentacles became in a few hours strongly
aggregated, showing that this salt had been absorbed and taken effect.

A short immersion in water for 20 m. did not retard the subsequent
action of the phosphate, or of splinters of glass placed on the glands;
but in two instances an immersion for 50 m. prevented any effect from a
solution of camphor. Several leaves which had been left for 20 m. in a
solution of one part of white sugar to 218 of water were placed in the
phosphate solution, the action of which was delayed; whereas a mixed
solution of sugar and the phosphate did not in the least interfere with
the effects of the latter. Three leaves, after being immersed for 20 m.
in the sugar solution, were placed in a solution of carbonate of
ammonia (one part to 218 of water); in 2 m. or 3 m. the glands were
blackened, and after 7 m. the tentacles were considerably inflected, so
that the solution of sugar, though it delayed the action of the
phosphate, did not delay that of the carbonate. Immersion in a similar
solution of gum arabic for 20 m. had no retarding action on the
phosphate. Three leaves were left for 20 m. in a mixture of one part of
alcohol to seven parts of water, [page 214] and then placed in the
phosphate solution: in 2 hrs. 15 m. there was a trace of inflection in
one leaf, and in 5 hrs. 30 m. a second was slightly affected; the
inflection subsequently increased, though slowly. Hence diluted
alcohol, which, as we shall see, is hardly at all poisonous, plainly
retards the subsequent action of the phosphate.

It was shown in the last chapter that leaves which did not become
inflected by nearly a day’s immersion in solutions of various salts and
acids behaved very differently from one another when subsequently
placed in the phosphate solution. I here give a table summing up the
results.

Column 1 : Name of the Salts and Acids in Solution. Column 2 : Period
of Immersion of the Leaves in Solutions of one part to 437 of water.
Column 3 : Effects produced on the Leaves by their subsequent Immersion
for stated periods in a Solution of one part of phosphate of ammonia to
8750 of water, or 1 gr. to 20 oz.

Rubidium chloride. : 22 hrs. : After 30 m. strong inflection of the
tentacles.

Potassium carbonate : 20 m. : Scarcely any inflection until 5 hrs. had
elapsed.

Calcium acetate. : 24 hrs. : After 24 hrs. very slight inflection.

Calcium nitrate. : 24 hrs. : Do. do.

Magnesium acetate. : 22 hrs. : Some slight inflection, which became
well pronounced in 24 hrs.

Magnesium nitrate. : 22 hrs. : After 4 hrs. 30 m. a fair amount of
inflection, which never increased.

Magnesium chloride : 22 hrs. : After a few minutes great inflection;
after 4 hrs. all four leaves with almost every tentacle closely
inflected.

Barium acetate. : 22 hrs. : After 24 hrs. two leaves out of four
slightly inflected.

Barium nitrate. : 22 hrs. : After 30 m. one leaf greatly, and two
others moderately, inflected; they remained thus for 24 hrs.

Strontium acetate. : 22 hrs. : After 25 m. two leaves greatly
inflected; after 8 hrs. a third leaf moderately, and the fourth very
slightly, inflected. All four thus remained for 24 hrs.

Strontium nitrate. : 22 hrs. : After 8 hrs. three leaves out of five
moderately inflected; after 24 hrs. all five in this state; but not one
closely inflected.

Aluminium chloride : 24 hrs. : Three leaves which had either been
slightly or not at all affected by the chloride became after 7 hrs. 30
m. rather closely inflected. [page 215]

Column 1 : Name of the Salts and Acids in Solution. Column 2 : Period
of Immersion of the Leaves in Solutions of one part to 437 of water.
Column 3 : Effects produced on the Leaves by their subsequent Immersion
for stated periods in a Solution of one part of phosphate of ammonia to
8750 of water, or 1 gr. to 20 oz.

Aluminium nitrate. : 24 hrs. : After 25 hrs. slight and doubtful
effect.

Lead chloride. : 23 hrs. : After 24 hrs. two leaves somewhat inflected,
the third very little; and thus remained.

Manganese chloride : 22 hrs. : After 48 hrs. not the least inflection.

Lactic acid. : 48 hrs. : After 24 hrs. a trace of inflection in a few
tentacles, the glands of which had not been killed by the acid.

Tannic acid. : 24 hrs. : After 24 hrs. no inflection.

Tartaric acid. : 24 hrs. : Do. do.

Citric acid. : 24 hrs. : After 50 m. tentacles decidedly inflected, and
after 5 hrs. strongly inflected; so remained for the next 24 hrs.

Formic acid. : 22 hrs. : Not observed until 24 hrs. had elapsed;
tentacles considerably inflected, and protoplasm aggregated.

In a large majority of these twenty cases, a varying degree of
inflection was slowly caused by the phosphate. In four cases, however,
the inflection was rapid, occurring in less than half an hour or at
most in 50 m. In three cases the phosphate did not produce the least
effect. Now what are we to infer from these facts? We know from ten
trials that immersion in distilled water for 24 hrs. prevents the
subsequent action of the phosphate solution. It would, therefore,
appear as if the solutions of chloride of manganese, tannic and
tartaric acids, which are not poisonous, acted exactly like water, for
the phosphate produced no effect on the leaves which had been
previously immersed in these three solutions. The majority of the other
solutions behaved to a certain extent like water, for the phosphate
produced, after a considerable interval of time, only a slight effect.
On the other hand, the leaves which had been immersed in the solutions
of the chloride of rubidium and magnesium, of acetate of strontium,
nitrate of barium, and citric acid, were quickly acted on by the
phosphate. Now was water absorbed from these five weak solutions, and
yet, owing to the presence of the salts, did not prevent the subsequent
action of the phosphate? Or [page 216] may we not suppose* that the
interstices of the walls of the glands were blocked up with the
molecules of these five substances, so that they were rendered
impermeable to water; for had water entered, we know from the ten
trials that the phosphate would not afterwards have produced any
effect? It further appears that the molecules of the carbonate of
ammonia can quickly pass into glands which, from having been immersed
for 20 m. in a weak solution of sugar, either absorb the phosphate very
slowly or are acted on by it very slowly. On the other hand, glands,
however they may have been treated, seem easily to permit the
subsequent entrance of the molecules of carbonate of ammonia. Thus
leaves which had been immersed in a solution (of one part to 437 of
water) of nitrate of potassium for 48 hrs.—of sulphate of potassium for
24 hrs.—and of the chloride of potassium for 25 hrs.—on being placed in
a solution of one part of carbonate of ammonia to 218 of water, had
their glands immediately blackened, and after 1 hr. their tentacles
somewhat inflected, and the protoplasm aggregated. But it would be an
endless task to endeavour to ascertain the wonderfully diversified
effects of various solutions on Drosera.

Alcohol (one part to seven of water).—It has already been shown that
half-minims of this strength placed on the discs of leaves do not cause
any inflection; and that when two days afterwards the leaves were given
bits of meat, they became strongly inflected. Four leaves were immersed
in this mixture, and two of them after 30 m. were brushed with a
camel-hair brush, like the leaves in the solution of camphor, but this
produced no effect.

* See Dr. M. Traube’s curious experiments on the production of
artificial cells, and on their permeability to various salts, described
in his papers: “Experimente zur Theorie der Zellenbildung und
Endosmose,” Breslau, 1866; and “Experimente zur physicalischen Erklrung
der Bildung der Zellhaut, ihres Wachsthums durch Intussusception,”
Breslau, 1874. These researches perhaps explain my results. Dr. Traube
commonly employed as a membrane the precipitate formed when tannic acid
comes into contact with a solution of gelatine. By allowing a
precipitation of sulphate of barium to take place at the same time, the
membrane becomes “infiltrated” with this salt; and in consequence of
the intercalation of molecules of sulphate of barium among those of the
gelatine precipitate, the molecular interstices in the membrane are
made smaller. In this altered condition, the membrane no longer allows
the passage through it of either sulphate of ammonia or nitrate of
barium, though it retains its permeability for water and chloride of
ammonia. [page 217]


Nor did these four leaves, on being left for 24 hrs. in the diluted
alcohol, undergo any inflection. They were then removed; one being
placed in an infusion of raw meat, and bits of meat on the discs of the
other three, with their stalks in water. Next day one seemed a little
injured, whilst two others showed merely a trace of inflection. We
must, however, bear in mind that immersion for 24 hrs. in water
prevents leaves from clasping meat. Hence alcohol of the above strength
is not poisonous, nor does it stimulate the leaves like camphor does.

The vapour of alcohol acts differently. A plant having three good
leaves was left for 25 m. under a receiver holding 19 oz. with sixty
minims of alcohol in a watch-glass. No movement ensued, but some few of
the glands were blackened and shrivelled, whilst many became quite
pale. These were scattered over all the leaves in the most irregular
manner, reminding me of the manner in which the glands were affected by
the vapour of carbonate of ammonia. Immediately on the removal of the
receiver particles of raw meat were placed on many of the glands, those
which retained their proper colour being chiefly selected. But not a
single tentacle was inflected during the next 4 hrs. After the first 2
hrs. the glands on all the tentacles began to dry; and next morning,
after 22 hrs., all three leaves appeared almost dead, with their glands
dry; the tentacles on one leaf alone being partially inflected.

A second plant was left for only 5 m. with some alcohol in a
watch-glass, under a 12-oz. receiver, and particles of meat were then
placed on the glands of several tentacles. After 10 m. some of them
began to curve inwards, and after 55 m. nearly all were considerably
inflected; but a few did not move. Some anaesthetic effect is here
probable, but by no means certain. A third plant was also left for 5 m.
under the same small vessel, with its whole inner surface wetted with
about a dozen drops of alcohol. Particles of meat were now placed on
the glands of several tentacles, some of which first began to move in
25 m.; after 40 m. most of them were somewhat inflected, and after 1
hr. 10 m. almost all were considerably inflected. From their slow rate
of movement there can be no doubt that the glands of these tentacles
had been rendered insensible for a time by exposure during 5 m. to the
vapour of alcohol.

Vapour of Chloroform.—The action of this vapour on Drosera is very
variable, depending, I suppose, on the constitution or age of the
plant, or on some unknown condition. It sometimes causes the tentacles
to move with extraordinary rapidity, and sometimes produces no such
effect. The glands are sometimes [page 218] rendered for a time
insensible to the action of raw meat, but sometimes are not thus
affected, or in a very slight degree. A plant recovers from a small
dose, but is easily killed by a larger one.

A plant was left for 30 m. under a bell-glass holding 19 fluid oz.
(539.6 ml.) with eight drops of chloroform, and before the cover was
removed, most of the tentacles became much inflected, though they did
not reach the centre. After the cover was removed, bits of meat were
placed on the glands of several of the somewhat incurved tentacles;
these glands were found much blackened after 6 hrs. 30 m., but no
further movement ensued. After 24 hrs. the leaves appeared almost dead.

A smaller bell-glass, holding 12 fluid oz. (340.8 ml.), was now
employed, and a plant was left for 90 s. under it, with only two drops
of chloroform. Immediately on the removal of the glass all the
tentacles curved inwards so as to stand perpendicularly up; and some of
them could actually be seen moving with extraordinary quickness by
little starts, and therefore in an unnatural manner; but they never
reached the centre. After 22 hrs. they fully re-expanded, and on meat
being placed on their glands, or when roughly touched by a needle, they
promptly became inflected; so that these leaves had not been in the
least injured.

Another plant was placed under the same small bell-glass with three
drops of chloroform, and before two minutes had elapsed, the tentacles
began to curl inwards with rapid little jerks. The glass was then
removed, and in the course of two or three additional minutes almost
every tentacle reached the centre. On several other occasions the
vapour did not excite any movement of this kind.

There seems also to be great variability in the degree and manner in
which chloroform renders the glands insensible to the subsequent action
of meat. In the plant last referred to, which had been exposed for 2 m.
to three drops of chloroform, some few tentacles curved up only to a
perpendicular position, and particles of meat were placed on their
glands; this caused them in 5 m. to begin moving, but they moved so
slowly that they did not reach the centre until 1 hr. 30 m. had
elapsed. Another plant was similarly exposed, that is, for 2 m. to
three drops of chloroform, and on particles of meat being placed on the
glands of several tentacles, which had curved up into a perpendicular
position, one of these began to bend in 8 m., but afterwards moved very
slowly; whilst none of the other tentacles [page 219] moved for the
next 40 m. Nevertheless, in 1 hr. 45 m. from the time when the bits of
meat had been given, all the tentacles reached the centre. In this case
some slight anaesthetic effect apparently had been produced. On the
following day the plant had perfectly recovered.

Another plant bearing two leaves was exposed for 2 m. under the 19-oz.
vessel to two drops of chloroform; it was then taken out and examined;
again exposed for 2 m. to two drops; taken out, and re-exposed for 3 m.
to three drops; so that altogether it was exposed alternately to the
air and during 7 m. to the vapour of seven drops of chloroform. Bits of
meat were now placed on thirteen glands on the two leaves. On one of
these leaves, a single tentacle first began moving in 40 m., and two
others in 54 m. On the second leaf some tentacles first moved in 1 hr.
11 m. After 2 hrs. many tentacles on both leaves were inflected; but
none had reached the centre within this time. In this case there could
not be the least doubt that the chloroform had exerted an anaesthetic
influence on the leaves.

On the other hand, another plant was exposed under the same vessel for
a much longer time, viz. 20 m., to twice as much chloroform. Bits of
meat were then placed on the glands of many tentacles, and all of them,
with a single exception, reached the centre in from 13 m. to 14 m. In
this case, little or no anaesthetic effect had been produced; and how
to reconcile these discordant results, I know not.

Vapour of Sulphuric Ether.—A plant was exposed for 30 m. to thirty
minims of this ether in a vessel holding 19 oz.; and bits of raw meat
were afterwards placed on many glands which had become pale-coloured;
but none of the tentacles moved. After 6 hrs. 30 m. the leaves appeared
sickly, and the discal glands were almost dry. By the next morning many
of the tentacles were dead, as were all those on which meat had been
placed; showing that matter had been absorbed from the meat which had
increased the evil effects of the vapour. After four days the plant
itself died. Another plant was exposed in the same vessel for 15 m. to
forty minims. One young, small, and tender leaf had all its tentacles
inflected, and seemed much injured. Bits of raw meat were placed on
several glands on two other and older leaves. These glands became dry
after 6 hrs.; and seemed injured; the tentacles never moved, excepting
one which was ultimately a little inflected. The glands of the other
tentacles continued to secrete, and appeared uninjured, but the whole
plant after three days became very sickly. [page 220]

In the two foregoing experiments the doses were evidently too large and
poisonous. With weaker doses, the anaesthetic effect was variable, as
in the case of chloroform. A plant was exposed for 5 m. to ten drops
under a 12-oz. vessel, and bits of meat were then placed on many
glands. None of the tentacles thus treated began to move in a decided
manner until 40 m. had elapsed; but then some of them moved very
quickly, so that two reached the centre after an additional interval of
only 10 m. In 2 hrs. 12 m. from the time when the meat was given, all
the tentacles reached the centre. Another plant, with two leaves, was
exposed in the same vessel for 5 m. to a rather larger dose of ether,
and bits of meat were placed on several glands. In this case one
tentacle on each leaf began to bend in 5 m.; and after 12 m. two
tentacles on one leaf, and one on the second leaf, reached the centre.
In 30 m. after the meat had been given, all the tentacles, both those
with and without meat, were closely inflected; so that the ether
apparently had stimulated these leaves, causing all the tentacles to
bend.

Vapour of Nitric Ether.—This vapour seems more injurious than that of
sulphuric ether. A plant was exposed for 5 m. in a 12-oz. vessel to
eight drops in a watch-glass, and I distinctly saw a few tentacles
curling inwards before the glass was removed. Immediately afterwards
bits of meat were placed on three glands, but no movement ensued in the
course of 18 m. The same plant was placed again under the same vessel
for 16 m. with ten drops of the ether. None of the tentacles moved, and
next morning those with the meat were still in the same position. After
48 hrs. one leaf seemed healthy, but the others were much injured.

Another plant, having two good leaves, was exposed for 6 m. under a
19-oz. vessel to the vapour from ten minims of the ether, and bits of
meat were then placed on the glands of many tentacles on both leaves.
After 36 m. several of them on one leaf became inflected, and after 1
hr. almost all the tentacles, those with and without meat, nearly
reached the centre. On the other leaf the glands began to dry in 1 hr.
40 m., and after several hours not a single tentacle was inflected; but
by the next morning, after 21 hrs., many were inflected, though they
seemed much injured. In this and the previous experiment, it is
doubtful, owing to the injury which the leaves had suffered, whether
any anaesthetic effect had been produced.

A third plant, having two good leaves, was exposed for only 4 m. in the
19-oz. vessel to the vapour from six drops. Bits of meat were then
placed on the glands of seven tentacles on the [page 221] same leaf. A
single tentacle moved after 1 hr. 23 m.; after 2 hrs. 3 m. several were
inflected; and after 3 hrs. 3 m. all the seven tentacles with meat were
well inflected. From the slowness of these movements it is clear that
this leaf had been rendered insensible for a time to the action of the
meat. A second leaf was rather differently affected; bits of meat were
placed on the glands of five tentacles, three of which were slightly
inflected in 28 m.; after 1 hr. 21 m. one reached the centre, but the
other two were still only slightly inflected; after 3 hrs. they were
much more inflected; but even after 5 hrs. 16 m. all five had not
reached the centre. Although some of the tentacles began to move
moderately soon, they afterwards moved with extreme slowness. By next
morning, after 20 hrs., most of the tentacles on both leaves were
closely inflected, but not quite regularly. After 48 hrs. neither leaf
appeared injured, though the tentacles were still inflected; after 72
hrs. one was almost dead, whilst the other was re-expanding and
recovering.

Carbonic Acid.—A plant was placed under a 122-oz. bell-glass filled
with this gas and standing over water; but I did not make sufficient
allowance for the absorption of the gas by the water, so that towards
the latter part of the experiment some air was drawn in. After an
exposure of 2 hrs. the plant was removed, and bits of raw meat placed
on the glands of three leaves. One of these leaves hung a little down,
and was at first partly and soon afterwards completely covered by the
water, which rose within the vessel as the gas was absorbed. On this
latter leaf the tentacles, to which meat had been given, became well
inflected in 2 m. 30 s., that is, at about the normal rate; so that
until I remembered that the leaf had been protected from the gas, and
might perhaps have absorbed oxygen from the water which was continually
drawn inwards, I falsely concluded that the carbonic acid had produced
no effect. On the other two leaves, the tentacles with meat behaved
very differently from those on the first leaf; two of them first began
to move slightly in 1 hr. 50 m., always reckoning from the time when
the meat was placed on the glands—were plainly inflected in 2 hrs. 22
m.—and in 3 hrs 22 m. reached the centre. Three other tentacles did not
begin to move until 2 hrs. 20 m. had elapsed, but reached the centre at
about the same time with the others, viz. in 3 hrs. 22 m.

This experiment was repeated several times with nearly the same
results, excepting that the interval before the tentacles began to move
varied a little. I will give only one other case. [page 222] A plant
was exposed in the same vessel to the gas for 45 m., and bits of meat
were then placed on four glands. But the tentacles did not move for 1
hr. 40 m.; after 2 hrs. 30 m. all four were well inflected, and after 3
hrs. reached the centre.

The following singular phenomenon sometimes, but by no means always,
occurred. A plant was immersed for 2 hrs., and bits of meat were then
placed on several glands. In the course of 13 m. all the submarginal
tentacles on one leaf became considerably inflected; those with the
meat not in the least degree more than the others. On a second leaf,
which was rather old, the tentacles with meat, as well as a few others,
were moderately inflected. On a third leaf all the tentacles were
closely inflected, though meat had not been placed on any of the
glands. This movement, I presume, may be attributed to excitement from
the absorption of oxygen. The last-mentioned leaf, to which no meat had
been given, was fully re-expanded after 24 hrs.; whereas the two other
leaves had all their tentacles closely inflected over the bits of meat
which by this time had been carried to their centres. Thus these three
leaves had perfectly recovered from the effects of the gas in the
course of 24 hrs.

On another occasion some fine plants, after having been left for 2 hrs.
in the gas, were immediately given bits of meat in the usual manner,
and on their exposure to the air most of their tentacles became in 12
m. curved into a vertical or sub-vertical position, but in an extremely
irregular manner; some only on one side of the leaf and some on the
other. They remained in this position for some time; the tentacles with
the bits of meat not having at first moved more quickly or farther
inwards than the others without meat. But after 2 hrs. 20 m. the former
began to move, and steadily went on bending until they reached the
centre. Next morning, after 22 hrs., all the tentacles on these leaves
were closely clasped over the meat which had been carried to their
centres; whilst the vertical and sub-vertical tentacles on the other
leaves to which no meat had been given had fully re-expanded. Judging,
however, from the subsequent action of a weak solution of carbonate of
ammonia on one of these latter leaves, it had not perfectly recovered
its excitability and power of movement in 22 hrs.; but another leaf,
after an additional 24 hrs., had completely recovered, judging from the
manner in which it clasped a fly placed on its disc.

I will give only one other experiment. After the exposure of a plant
for 2 hrs. to the gas, one of its leaves was immersed in a rather
strong solution of carbonate of ammonia, together with [page 223] a
fresh leaf from another plant. The latter had most of its tentacles
strongly inflected within 30 m.; whereas the leaf which had been
exposed to the carbonic acid remained for 24 hrs. in the solution
without undergoing any inflection, with the exception of two tentacles.
This leaf had been almost completely paralysed, and was not able to
recover its sensibility whilst still in the solution, which from having
been made with distilled water probably contained little oxygen.]

Concluding Remarks on the Effects of the foregoing Agents.—As the
glands, when excited, transmit some influence to the surrounding
tentacles, causing them to bend and their glands to pour forth an
increased amount of modified secretion, I was anxious to ascertain
whether the leaves included any element having the nature of
nerve-tissue, which, though not continuous, served as the channel of
transmission. This led me to try the several alkaloids and other
substances which are known to exert a powerful influence on the nervous
system of animals; I was at first encouraged in my trials by finding
that strychnine, digitaline, and nicotine, which all act on the nervous
system, were poisonous to Drosera, and caused a certain amount of
inflection. Hydrocyanic acid, again, which is so deadly a poison to
animals, caused rapid movement of the tentacles. But as several
innocuous acids, though much diluted, such as benzoic, acetic, &c., as
well as some essential oils, are extremely poisonous to Drosera, and
quickly cause strong inflection, it seems probable that strychnine,
nicotine, digitaline, and hydrocyanic acid, excite inflection by acting
on elements in no way analogous to the nerve-cells of animals. If
elements of this latter nature had been present in the leaves, it might
have been expected that morphia, hyoscyamus, atropine, veratrine,
colchicine, curare, and diluted alcohol would have produced some marked
effect; whereas [page 224] these substances are not poisonous and have
no power, or only a very slight one, of inducing inflection. It should,
however, be observed that curare, colchicine, and veratrine are
muscle-poisons—that is, act on nerves having some special relation with
the muscles, and, therefore, could not be expected to act on Drosera.
The poison of the cobra is most deadly to animals, by paralysing their
nerve-centres,* yet is not in the least so to Drosera, though quickly
causing strong inflection.

Notwithstanding the foregoing facts, which show how widely different is
the effect of certain substances on the health or life of animals and
of Drosera, yet there exists a certain degree of parallelism in the
action of certain other substances. We have seen that this holds good
in a striking manner with the salts of sodium and potassium. Again,
various metallic salts and acids, namely those of silver, mercury,
gold, tin, arsenic, chromium, copper, and platina, most or all of which
are highly poisonous to animals, are equally so to Drosera. But it is a
singular fact that the chloride of lead and two salts of barium were
not poisonous to this plant. It is an equally strange fact, that,
though acetic and propionic acids are highly poisonous, their ally,
formic acid, is not so; and that, whilst certain vegetable acids,
namely oxalic, benzoic, &c., are poisonous in a high degree, gallic,
tannic, tartaric, and malic (all diluted to an equal degree) are not
so. Malic acid induces inflection, whilst the three other just named
vegetable acids have no such power. But a pharmacopoeia would be
requisite to describe the diversified effects of various substances on
Drosera.**

* Dr. Fayrer, ‘The Thanatophidia of India,’ 1872, p. 4.


** Seeing that acetic, hydrocyanic, and chromic acids, acetate of
strychnine, and vapour of ether, are poisonous to Drosera, [[page 225]]
it is remarkable that Dr. Ransom (‘Philosoph. Transact.’ 1867, p. 480),
who used much stronger solutions of these substances than I did, states
“that the rhythmic contractility of the yolk (of the ova of the pike)
is not materially influenced by any of the poisons used, which did not
act chemically, with the exception of chloroform and carbonic acid.” I
find it stated by several writers that curare has no influence on
sarcode or protoplasm, and we have seen that, though curare excites
some degree of inflection, it causes very little aggregation of the
protoplasm.) [page 226]


Of the alkaloids and their salts which were tried, several had not the
least power of inducing inflection; others, which were certainly
absorbed, as shown by the changed colour of the glands, had but a very
moderate power of this kind; others, again, such as the acetate of
quinine and digitaline, caused strong inflection.

The several substances mentioned in this chapter affect the colour of
the glands very differently. These often become dark at first, and then
very pale or white, as was conspicuously the case with glands subjected
to the poison of the cobra and citrate of strychnine. In other cases
they are from the first rendered white, as with leaves placed in hot
water and several acids; and this, I presume, is the result of the
coagulation of the albumen. On the same leaf some glands become white
and others dark-coloured, as occurred with leaves in a solution of the
sulphate of quinine, and in the vapour of alcohol. Prolonged immersion
in nicotine, curare, and even water, blackens the glands; and this, I
believe, is due to the aggregation of the protoplasm within their
cells. Yet curare caused very little aggregation in the cells of the
tentacles, whereas nicotine and sulphate of quinine induced strongly
marked aggregation down their bases. The aggregated masses in leaves
which had been immersed for 3 hrs. 15 m. in a saturated solution of
sulphate of quinine exhibited incessant [page 226] changes of form, but
after 24 hrs. were motionless; the leaf being flaccid and apparently
dead. On the other hand, with leaves subjected for 48 hrs. to a strong
solution of the poison of the cobra, the protoplasmic masses were
unusually active, whilst with the higher animals the vibratile cilia
and white corpuscles of the blood seem to be quickly paralysed by this
substance.

With the salts of alkalies and earths, the nature of the base, and not
that of the acid, determines their physiological action on Drosera, as
is likewise the case with animals; but this rule hardly applies to the
salts of quinine and strychnine, for the acetate of quinine causes much
more inflection than the sulphate, and both are poisonous, whereas the
nitrate of quinine is not poisonous, and induces inflection at a much
slower rate than the acetate. The action of the citrate of strychnine
is also somewhat different from that of the sulphate.

Leaves which have been immersed for 24 hrs. in water, and for only 20
m. in diluted alcohol, or in a weak solution of sugar, are afterwards
acted on very slowly, or not at all, by the phosphate of ammonia,
though they are quickly acted on by the carbonate. Immersion for 20 m.
in a solution of gum arabic has no such inhibitory power. The solutions
of certain salts and acids affect the leaves, with respect to the
subsequent action of the phosphate, exactly like water, whilst others
allow the phosphate afterwards to act quickly and energetically. In
this latter case, the interstices of the cell-walls may have been
blocked up by the molecules of the salts first given in solution, so
that water could not afterwards enter, though the molecules of the
phosphate could do so, and those of the carbonate still more easily.
[page 227]

The action of camphor dissolved in water is remarkable, for it not only
soon induces inflection, but apparently renders the glands extremely
sensitive to mechanical irritation; for if they are brushed with a soft
brush, after being immersed in the solution for a short time, the
tentacles begin to bend in about 2 m. It may, however, be that the
brushing, though not a sufficient stimulus by itself, tends to excite
movement merely by reinforcing the direct action of the camphor. The
vapour of camphor, on the other hand, serves as a narcotic.

Some essential oils, both in solution and in vapour, cause rapid
inflection, others have no such power; those which I tried were all
poisonous.

Diluted alcohol (one part to seven of water) is not poisonous, does not
induce inflection, nor increase the sensitiveness of the glands to
mechanical irritation. The vapour acts as a narcotic or anaesthetic,
and long exposure to it kills the leaves.

The vapours of chloroform, sulphuric and nitric ether, act in a
singularly variable manner on different leaves, and on the several
tentacles of the same leaf. This, I suppose, is owing to differences in
the age or constitution of the leaves, and to whether certain tentacles
have lately been in action. That these vapours are absorbed by the
glands is shown by their changed colour; but as other plants not
furnished with glands are affected by these vapours, it is probable
that they are likewise absorbed by the stomata of Drosera. They
sometimes excite extraordinarily rapid inflection, but this is not an
invariable result. If allowed to act for even a moderately long time,
they kill the leaves; whilst a small dose acting for only a short time
serves as a narcotic or anaesthetic. In this case the tentacles,
whether or not they have [page 228] become inflected, are not excited
to further movement by bits of meat placed on the glands, until some
considerable time has elapsed. It is generally believed that with
animals and plants these vapours act by arresting oxidation.

Exposure to carbonic acid for 2 hrs., and in one case for only 45 m.,
likewise rendered the glands insensible for a time to the powerful
stimulus of raw meat. The leaves, however, recovered their full powers,
and did not seem in the least injured, on being left in the air for 24
or 48 hrs. We have seen in the third chapter that the process of
aggregation in leaves subjected for two hours to this gas and then
immersed in a solution of the carbonate of ammonia is much retarded, so
that a considerable time elapses before the protoplasm in the lower
cells of the tentacles becomes aggregated. In some cases, soon after
the leaves were removed from the gas and brought into the air, the
tentacles moved spontaneously; this being due, I presume, to the
excitement from the access of oxygen. These inflected tentacles,
however, could not be excited for some time afterwards to any further
movement by their glands being stimulated. With other irritable plants
it is known* that the exclusion of oxygen prevents their moving, and
arrests the movements of the protoplasm within their cells, but this
arrest is a different phenomenon from the retardation of the process of
aggregation just alluded to. Whether this latter fact ought to be
attributed to the direct action of the carbonic acid, or to the
exclusion of oxygen, I know not.

* Sachs, ‘Traité de Bot.’ 1874, pp. 846, 1037. [page 229]




CHAPTER X.
ON THE SENSITIVENESS OF THE LEAVES, AND ON THE LINES OF TRANSMISSION OF
THE MOTOR IMPULSE.


Glands and summits of the tentacles alone sensitive—Transmission of the
motor impulse down the pedicels of the tentacles, and across the blade
of the leaf—Aggregation of the protoplasm, a reflex action—First
discharge of the motor impulse sudden—Direction of the movements of the
tentacles—Motor impulse transmitted through the cellular tissue—
Mechanism of the movements—Nature of the motor impulse—Re-expansion of
the tentacles.


We have seen in the previous chapters that many widely different
stimulants, mechanical and chemical, excite the movement of the
tentacles, as well as of the blade of the leaf; and we must now
consider, firstly, what are the points which are irritable or
sensitive, and secondly how the motor impulse is transmitted from one
point to another. The glands are almost exclusively the seat of
irritability, yet this irritability must extend for a very short
distance below them; for when they were cut off with a sharp pair of
scissors without being themselves touched, the tentacles often became
inflected. These headless tentacles frequently re-expanded; and when
afterwards drops of the two most powerful known stimulants were placed
on the cut-off ends, no effect was produced. Nevertheless these
headless tentacles are capable of subsequent inflection if excited by
an impulse sent from the disc. I succeeded on several occasions in
crushing glands between fine pincers, but this did not excite any
movement; nor did raw meat and salts of ammonia, when placed on such
crushed glands. [page 230] It is probable that they were killed so
instantly that they were not able to transmit any motor impulse; for in
six observed cases (in two of which however the gland was quite pinched
off) the protoplasm within the cells of the tentacles did not become
aggregated; whereas in some adjoining tentacles, which were inflected
from having been roughly touched by the pincers, it was well
aggregated. In like manner the protoplasm does not become aggregated
when a leaf is instantly killed by being dipped into boiling water. On
the other hand, in several cases in which tentacles became inflected
after their glands had been cut off with sharp scissors, a distinct
though moderate degree of aggregation supervened.

The pedicels of the tentacles were roughly and repeatedly rubbed; raw
meat or other exciting substances were placed on them, both on the
upper surface near the base and elsewhere, but no distinct movement
ensued. Some bits of meat, after being left for a considerable time on
the pedicels, were pushed upwards, so as just to touch the glands, and
in a minute the tentacles began to bend. I believe that the blade of
the leaf is not sensitive to any stimulant. I drove the point of a
lancet through the blades of several leaves, and a needle three or four
times through nineteen leaves: in the former case no movement ensued;
but about a dozen of the leaves which were repeatedly pricked had a few
tentacles irregularly inflected. As, however, their backs had to be
supported during the operation, some of the outer glands, as well as
those on the disc, may have been touched; and this perhaps sufficed to
cause the slight degree of movement observed. Nitschke*says

* ‘Bot. Zeitung,’ 1860, p. 234. [page 231]


that cutting and pricking the leaf does not excite movement. The
petiole of the leaf is quite insensible.

The backs of the leaves bear numerous minute papillae, which do not
secrete, but have the power of absorption. These papillae are, I
believe, rudiments of formerly existing tentacles together with their
glands. Many experiments were made to ascertain whether the backs of
the leaves could be irritated in any way, thirty-seven leaves being
thus tried. Some were rubbed for a long time with a blunt needle, and
drops of milk and other exciting fluids, raw meat, crushed flies, and
various substances, placed on others. These substances were apt soon to
become dry, showing that no secretion had been excited. Hence I
moistened them with saliva, solutions of ammonia, weak hydrochloric
acid, and frequently with the secretion from the glands of other
leaves. I also kept some leaves, on the backs of which exciting objects
had been placed, under a damp bell-glass; but with all my care I never
saw any true movement. I was led to make so many trials because,
contrary to my previous experience, Nitschke states* that, after
affixing objects to the backs of leaves by the aid of the viscid
secretion, he repeatedly saw the tentacles (and in one instance the
blade) become reflexed. This movement, if a true one, would be most
anomalous; for it implies that the tentacles receive a motor impulse
from an unnatural source, and have the power of bending in a direction
exactly the reverse of that which is habitual to them; this power not
being of the least use to the plant, as insects cannot adhere to the
smooth backs of the leaves.

I have said that no effect was produced in the above

* ‘Bot. Zeitung.’ 1860, p. 437. [page 232]


cases; but this is not strictly true, for in three instances a little
syrup was added to the bits of raw meat on the backs of leaves, in
order to keep them damp for a time; and after 36 hrs. there was a trace
of reflexion in the tentacles of one leaf, and certainly in the blade
of another. After twelve additional hours, the glands began to dry, and
all three leaves seemed much injured. Four leaves were then placed
under a bell-glass, with their footstalks in water, with drops of syrup
on their backs, but without any meat. Two of these leaves, after a day,
had a few tentacles reflexed. The drops had now increased considerably
in size, from having imbibed moisture, so as to trickle down the backs
of the tentacles and footstalks. On the second day, one leaf had its
blade much reflexed; on the third day the tentacles of two were much
reflexed, as well as the blades of all four to a greater or less
degree. The upper side of one leaf, instead of being, as at first,
slightly concave, now presented a strong convexity upwards. Even on the
fifth day the leaves did not appear dead. Now, as sugar does not in the
least excite Drosera, we may safely attribute the reflexion of the
blades and tentacles of the above leaves to exosmose from the cells
which were in contact with the syrup, and their consequent contraction.
When drops of syrup are placed on the leaves of plants with their roots
still in damp earth, no inflection ensues, for the roots, no doubt,
pump up water as quickly as it is lost by exosmose. But if cut-off
leaves are immersed in syrup, or in any dense fluid, the tentacles are
greatly, though irregularly, inflected, some of them assuming the shape
of corkscrews; and the leaves soon become flaccid. If they are now
immersed in a fluid of low specific gravity, the tentacles re-expand.
From these [page 233] facts we may conclude that drops of syrup placed
on the backs of leaves do not act by exciting a motor impulse which is
transmitted to the tentacles; but that they cause reflexion by inducing
exosmose. Dr. Nitschke used the secretion for sticking insects to the
backs of the leaves; and I suppose that he used a large quantity, which
from being dense probably caused exosmose. Perhaps he experimented on
cut-off leaves, or on plants with their roots not supplied with enough
water.

As far, therefore, as our present knowledge serves, we may conclude
that the glands, together with the immediately underlying cells of the
tentacles, are the exclusive seats of that irritability or
sensitiveness with which the leaves are endowed. The degree to which a
gland is excited can be measured only by the number of the surrounding
tentacles which are inflected, and by the amount and rate of their
movement. Equally vigorous leaves, exposed to the same temperature (and
this is an important condition), are excited in different degrees under
the following circumstances. A minute quantity of a weak solution
produces no effect; add more, or give a rather stronger solution, and
the tentacles bend. Touch a gland once or twice, and no movement
follows; touch it three or four times, and the tentacle becomes
inflected. But the nature of the substance which is given is a very
important element: if equal-sized particles of glass (which acts only
mechanically), of gelatine, and raw meat, are placed on the discs of
several leaves, the meat causes far more rapid, energetic, and widely
extended movement than the two former substances. The number of glands
which are excited also makes a great difference in the result: place a
bit of meat on one or two of the discal [page 234] glands, and only a
few of the immediately surrounding short tentacles are inflected; place
it on several glands, and many more are acted on; place it on thirty or
forty, and all the tentacles, including the extreme marginal ones,
become closely inflected. We thus see that the impulses proceeding from
a number of glands strengthen one another, spread farther, and act on a
larger number of tentacles, than the impulse from any single gland.

Transmission of the Motor Impulse.—In every case the impulse from a
gland has to travel for at least a short distance to the basal part of
the tentacle, the upper part and the gland itself being merely carried
by the inflection of the lower part. The impulse is thus always
transmitted down nearly the whole length of the pedicel. When the
central glands are stimulated, and the extreme marginal tentacles
become inflected, the impulse is transmitted across half the diameter
of the disc; and when the glands on one side of the disc are
stimulated, the impulse is transmitted across nearly the whole width of
the disc. A gland transmits its motor impulse far more easily and
quickly down its own tentacle to the bending place than across the disc
to neighbouring tentacles. Thus a minute dose of a very weak solution
of ammonia, if given to one of the glands of the exterior tentacles,
causes it to bend and reach the centre; whereas a large drop of the
same solution, given to a score of glands on the disc, will not cause
through their combined influence the least inflection of the exterior
tentacles. Again, when a bit of meat is placed on the gland of an
exterior tentacle, I have seen movement in ten seconds, and repeatedly
within a minute; but a much larger bit placed on several glands on the
disc does not cause [page 235] the exterior tentacles to bend until
half an hour or even several hours have elapsed.

The motor impulse spreads gradually on all sides from one or more
excited glands, so that the tentacles which stand nearest are always
first affected. Hence, when the glands in the centre of the disc are
excited, the extreme marginal tentacles are the last inflected. But the
glands on different parts of the leaf transmit their motor power in a
somewhat different manner. If a bit of meat be placed on the
long-headed gland of a marginal tentacle, it quickly transmits an
impulse to its own bending portion; but never, as far as I have
observed, to the adjoining tentacles; for these are not affected until
the meat has been carried to the central glands, which then radiate
forth their conjoint impulse on all sides. On four occasions leaves
were prepared by removing some days previously all the glands from the
centre, so that these could not be excited by the bits of meat brought
to them by the inflection of the marginal tentacles; and now these
marginal tentacles re-expanded after a time without any other tentacle
being affected. Other leaves were similarly prepared, and bits of meat
were placed on the glands of two tentacles in the third row from the
outside, and on the glands of two tentacles in the fifth row. In these
four cases the impulse was sent in the first place laterally, that is,
in the same concentric row of tentacles, and then towards the centre;
but not centrifugally, or towards the exterior tentacles. In one of
these cases only a single tentacle on each side of the one with meat
was affected. In the three other cases, from half a dozen to a dozen
tentacles, both laterally and towards the centre, were well inflected
or sub-inflected. Lastly, in [page 236] ten other experiments, minute
bits of meat were placed on a single gland or on two glands in the
centre of the disc. In order that no other glands should touch the
meat, through the inflection of the closely adjoining short tentacles,
about half a dozen glands had been previously removed round the
selected ones. On eight of these leaves from sixteen to twenty-five of
the short surrounding tentacles were inflected in the course of one or
two days; so that the motor impulse radiating from one or two of the
discal glands is able to produce this much effect. The tentacles which
had been removed are included in the above numbers; for, from standing
so close, they would certainly have been affected. On the two remaining
leaves, almost all the short tentacles on the disc were inflected. With
a more powerful stimulus than meat, namely a little phosphate of lime
moistened with saliva, I have seen the inflection spread still farther
from a single gland thus treated; but even in this case the three or
four outer rows of tentacles were not affected. From these experiments
it appears that the impulse from a single gland on the disc acts on a
greater number of tentacles than that from a gland of one of the
exterior elongated tentacles; and this probably follows, at least in
part, from the impulse having to travel a very short distance down the
pedicels of the central tentacles, so that it is able to spread to a
considerable distance all round.

Whilst examining these leaves, I was struck with the fact that in six,
perhaps seven, of them the tentacles were much more inflected at the
distal and proximal ends of the leaf (i.e. towards the apex and base)
than on either side; and yet the tentacles on the sides stood as near
to the gland where the bit of meat lay as did those at the two ends. It
thus appeared as [page 237] if the motor impulse was transmitted from
the centre across the disc more readily in a longitudinal than in a
transverse direction; and as this appeared a new and interesting fact
in the physiology of plants, thirty-five fresh experiments were made to
test its truth. Minute bits of meat were placed on a single gland or on
a few glands, on the right or left side of the discs of eighteen
leaves; other bits of the same size being placed on the distal or
proximal ends of seventeen other leaves. Now if the motor impulse were
transmitted with equal force or at an equal rate through the blade in
all directions, a bit of meat placed at one side or at one end of the
disc ought to affect equally all the tentacles situated at an equal
distance from it; but this certainly is not the case. Before giving the
general results, it may be well to describe three or four rather
unusual cases.

[(1) A minute fragment of a fly was placed on one side of the disc, and
after 32 m. seven of the outer tentacles near the fragment were
inflected; after 10 hrs. several more became so, and after 23 hrs. a
still greater number; and now the blade of the leaf on this side was
bent inwards so as to stand up at right angles to the other side.
Neither the blade of the leaf nor a single tentacle on the opposite
side was affected; the line of separation between the two halves
extending from the footstalk to the apex. The leaf remained in this
state for three days, and on the fourth day began to re-expand; not a
single tentacle having been inflected on the opposite side.

(2) I will here give a case not included in the above thirty-five
experiments. A small fly was found adhering by its feet to the left
side of the disc. The tentacles on this side soon closed in and killed
the fly; and owing probably to its struggle whilst alive, the leaf was
so much excited that in about 24 hrs. all the tentacles on the opposite
side became inflected; but as they found no prey, for their glands did
not reach the fly, they re-expanded in the course of 15 hrs.; the
tentacles on the left side remaining clasped for several days.

(3) A bit of meat, rather larger than those commonly used, [page 238]
was placed in a medial line at the basal end of the disc, near the
footstalk; after 2 hrs. 30 m. some neighbouring tentacles were
inflected; after 6 hrs. the tentacles on both sides of the footstalk,
and some way up both sides, were moderately inflected; after 8 hrs. the
tentacles at the further or distal end were more inflected than those
on either side; after 23 hrs. the meat was well clasped by all the
tentacles, excepting by the exterior ones on the two sides.

(4) Another bit of meat was placed at the opposite or distal end of
another leaf, with exactly the same relative results.

(5) A minute bit of meat was placed on one side of the disc; next day
the neighbouring short tentacles were inflected, as well as in a slight
degree three or four on the opposite side near the footstalk. On the
second day these latter tentacles showed signs of re-expanding, so I
added a fresh bit of meat at nearly the same spot, and after two days
some of the short tentacles on the opposite side of the disc were
inflected. As soon as these began to re-expand, I added another bit of
meat, and next day all the tentacles on the opposite side of the disc
were inflected towards the meat; whereas we have seen that those on the
same side were affected by the first bit of meat which was given.]

Now for the general results. Of the eighteen leaves on which bits of
meat were placed on the right or left sides of the disc, eight had a
vast number of tentacles inflected on the same side, and in four of
them the blade itself on this side was likewise inflected; whereas not
a single tentacle nor the blade was affected on the opposite side.
These leaves presented a very curious appearance, as if only the
inflected side was active, and the other paralysed. In the remaining
ten cases, a few tentacles became inflected beyond the medial line, on
the side opposite to that where the meat lay; but, in some of these
cases, only at the proximal or distal ends of the leaves. The
inflection on the opposite side always occurred considerably after that
on the same side, and in one instance not until the fourth day. We have
also seen [page 239] with No. 5 that bits of meat had to be added
thrice before all the short tentacles on the opposite side of the disc
were inflected.

The result was widely different when bits of meat were placed in a
medial line at the distal or proximal ends of the disc. In three of the
seventeen experiments thus made, owing either to the state of the leaf
or to the smallness of the bit of meat, only the immediately adjoining
tentacles were affected; but in the other fourteen cases the tentacles
at the opposite end of the leaf were inflected, though these were as
distant from where the meat lay as were those on one side of the disc
from the meat on the opposite side. In some of the present cases the
tentacles on the sides were not at all affected, or in a less degree,
or after a longer interval of time, than those at the opposite end. One
set of experiments is worth giving in fuller detail. Cubes of meat, not
quite so small as those usually employed, were placed on one side of
the discs of four leaves, and cubes of the same size at the proximal or
distal end of four other leaves. Now, when these two sets of leaves
were compared after an interval of 24 hrs., they presented a striking
difference. Those having the cubes on one side were very slightly
affected on the opposite side; whereas those with the cubes at either
end had almost every tentacle at the opposite end, even the marginal
ones, closely inflected. After 48 hrs. the contrast in the state of the
two sets was still great; yet those with the meat on one side now had
their discal and submarginal tentacles on the opposite side somewhat
inflected, this being due to the large size of the cubes. Finally we
may conclude from these thirty-five experiments, not to mention the six
or seven previous ones, that the motor impulse is transmitted from any
single gland [page 240] or small group of glands through the blade to
the other tentacles more readily and effectually in a longitudinal than
in a transverse direction.

As long as the glands remain excited, and this may last for many days,
even for eleven, as when in contact with phosphate of lime, they
continue to transmit a motor impulse to the basal and bending parts of
their own pedicels, for otherwise they would re-expand. The great
difference in the length of time during which tentacles remain
inflected over inorganic objects, and over objects of the same size
containing soluble nitrogenous matter, proves the same fact. But the
intensity of the impulse transmitted from an excited gland, which has
begun to pour forth its acid secretion and is at the same time
absorbing, seems to be very small compared with that which it transmits
when first excited. Thus, when moderately large bits of meat were
placed on one side of the disc, and the discal and sub-marginal
tentacles on the opposite side became inflected, so that their glands
at last touched the meat and absorbed matter from it, they did not
transmit any motor influence to the exterior rows of tentacles on the
same side, for these never became inflected. If, however, meat had been
placed on the glands of these same tentacles before they had begun to
secrete copiously and to absorb, they undoubtedly would have affected
the exterior rows. Nevertheless, when I gave some phosphate of lime,
which is a most powerful stimulant, to several submarginal tentacles
already considerably inflected, but not yet in contact with some
phosphate previously placed on two glands in the centre of the disc,
the exterior tentacles on the same side were acted on.

When a gland is first excited, the motor impulse is discharged within a
few seconds, as we know from the [page 241] bending of the tentacle;
and it appears to be discharged at first with much greater force than
afterwards. Thus, in the case above given of a small fly naturally
caught by a few glands on one side of a leaf, an impulse was slowly
transmitted from them across the whole breadth of the leaf, causing the
opposite tentacles to be temporarily inflected, but the glands which
remained in contact with the insect, though they continued for several
days to send an impulse down their own pedicels to the bending place,
did not prevent the tentacles on the opposite side from quickly
re-expanding; so that the motor discharge must at first have been more
powerful than afterwards.

When an object of any kind is placed on the disc, and the surrounding
tentacles are inflected, their glands secrete more copiously and the
secretion becomes acid, so that some influence is sent to them from the
discal glands. This change in the nature and amount of the secretion
cannot depend on the bending of the tentacles, as the glands of the
short central tentacles secrete acid when an object is placed on them,
though they do not themselves bend. Therefore I inferred that the
glands of the disc sent some influence up the surrounding tentacles to
their glands, and that these reflected back a motor impulse to their
basal parts; but this view was soon proved erroneous. It was found by
many trials that tentacles with their glands closely cut off by sharp
scissors often become inflected and again re-expand, still appearing
healthy. One which was observed continued healthy for ten days after
the operation. I therefore cut the glands off twenty-five tentacles, at
different times and on different leaves, and seventeen of these soon
became inflected, and afterwards re-expanded. The re-expansion
commenced in about [page 242] 8 hrs. or 9 hrs., and was completed in
from 22 hrs. to 30 hrs. from the time of inflection. After an interval
of a day or two, raw meat with saliva was placed on the discs of these
seventeen leaves, and when observed next day, seven of the headless
tentacles were inflected over the meat as closely as the uninjured ones
on the same leaves; and an eighth headless tentacle became inflected
after three additional days. The meat was removed from one of these
leaves, and the surface washed with a little stream of water, and after
three days the headless tentacle re-expanded for the second time. These
tentacles without glands were, however, in a different state from those
provided with glands and which had absorbed matter from the meat, for
the protoplasm within the cells of the former had undergone far less
aggregation. From these experiments with headless tentacles it is
certain that the glands do not, as far as the motor impulse is
concerned, act in a reflex manner like the nerve-ganglia of animals.

But there is another action, namely that of aggregation, which in
certain cases may be called reflex, and it is the only known instance
in the vegetable kingdom. We should bear in mind that the process does
not depend on the previous bending of the tentacles, as we clearly see
when leaves are immersed in certain strong solutions. Nor does it
depend on increased secretion from the glands, and this is shown by
several facts, more especially by the papillae, which do not secrete,
yet undergoing aggregation, if given carbonate of ammonia or an
infusion of raw meat. When a gland is directly stimulated in any way,
as by the pressure of a minute particle of glass, the protoplasm within
the cells of the gland first becomes aggregated, then that in the cells
immediately beneath the gland, and so lower and lower down the
tentacles to their bases;— [page 243] that is, if the stimulus has been
sufficient and not injurious. Now, when the glands of the disc are
excited, the exterior tentacles are affected in exactly the same
manner: the aggregation always commences in their glands, though these
have not been directly excited, but have only received some influence
from the disc, as shown by their increased acid secretion. The
protoplasm within the cells immediately beneath the glands are next
affected, and so downwards from cell to cell to the bases of the
tentacles. This process apparently deserves to be called a reflex
action, in the same manner as when a sensory nerve is irritated, and
carries an impression to a ganglion which sends back some influence to
a muscle or gland, causing movement or increased secretion; but the
action in the two cases is probably of a widely different nature. After
the protoplasm in a tentacle has been aggregated, its redissolution
always begins in the lower part, and slowly travels up the pedicel to
the gland, so that the protoplasm last aggregated is first redissolved.
This probably depends merely on the protoplasm being less and less
aggregated, lower and lower down in the tentacles, as can be seen
plainly when the excitement has been slight. As soon, therefore, as the
aggregating action altogether ceases, redissolution naturally commences
in the less strongly aggregated matter in the lowest part of the
tentacle, and is there first completed.

Direction of the Inflected Tentacles.—When a particle of any kind is
placed on the gland of one of the outer tentacles, this invariably
moves towards the centre of the leaf; and so it is with all the
tentacles of a leaf immersed in any exciting fluid. The glands of the
exterior tentacles then form a ring round the middle part of the disc,
as shown in a previous figure (fig. 4, [page 244] p. 10). The short
tentacles within this ring still retain their vertical position, as
they likewise do when a large object is placed on their glands, or when
an insect is caught by them. In this latter case we can see that the
inflection of the short central tentacles would be useless, as their
glands are already in contact with their prey.

FIG. 10. (Drosera rotundifolia.) Leaf (enlarged) with the tentacles
inflected over a bit of meat placed on one side of the disc.

The result is very different when a single gland on one side of the
disc is excited, or a few in a group. These send an impulse to the
surrounding tentacles, which do not now bend towards the centre of the
leaf, but to the point of excitement. We owe this capital observation
to Nitschke,* and since reading his paper a few years ago, I have
repeatedly verified it. If a minute bit of meat be placed by the aid of
a needle on a single gland, or on three or four together, halfway
between the centre and the circumference of the disc, the directed
movement of the surrounding tentacles is well exhibited. An accurate
drawing of a leaf with meat in this position is here reproduced (fig.
10), and we see the tentacles, including some of the exterior ones,
accurately directed to the point where the meat lay. But a much better

* ‘Bot. Zeitung,’ 1860, p. 240. [page 245]


plan is to place a particle of the phosphate of lime moistened with
saliva on a single gland on one side of the disc of a large leaf, and
another particle on a single gland on the opposite side. In four such
trials the excitement was not sufficient to affect the outer tentacles,
but all those near the two points were directed to them, so that two
wheels were formed on the disc of the same leaf; the pedicels of the
tentacles forming the spokes, and the glands united in a mass over the
phosphate representing the axles. The precision with which each
tentacle pointed to the particle was wonderful; so that in some cases I
could detect no deviation from perfect accuracy. Thus, although the
short tentacles in the middle of the disc do not bend when their glands
are excited in a direct manner, yet if they receive a motor impulse
from a point on one side, they direct themselves to the point equally
well with the tentacles on the borders of the disc.

In these experiments, some of the short tentacles on the disc, which
would have been directed to the centre, had the leaf been immersed in
an exciting fluid, were now inflected in an exactly opposite direction,
viz. towards the circumference. These tentacles, therefore, had
deviated as much as 180o from the direction which they would have
assumed if their own glands had been stimulated, and which may be
considered as the normal one. Between this, the greatest possible and
no deviation from the normal direction, every degree could be observed
in the tentacles on these several leaves. Notwithstanding the precision
with which the tentacles generally were directed, those near the
circumference of one leaf were not accurately directed towards some
phosphate of lime at a rather distant point on the opposite side of the
disc. It appeared as if the motor [page 246] impulse in passing
transversely across nearly the whole width of the disc had departed
somewhat from a true course. This accords with what we have already
seen of the impulse travelling less readily in a transverse than in a
longitudinal direction. In some other cases, the exterior tentacles did
not seem capable of such accurate movement as the shorter and more
central ones.

Nothing could be more striking than the appearance of the above four
leaves, each with their tentacles pointing truly to the two little
masses of the phosphate on their discs. We might imagine that we were
looking at a lowly organised animal seizing prey with its arms. In the
case of Drosera the explanation of this accurate power of movement, no
doubt, lies in the motor impulse radiating in all directions, and
whichever side of a tentacle it first strikes, that side contracts, and
the tentacle consequently bends towards the point of excitement. The
pedicels of the tentacles are flattened, or elliptic in section. Near
the bases of the short central tentacles, the flattened or broad face
is formed of about five longitudinal rows of cells; in the outer
tentacles of the disc it consists of about six or seven rows; and in
the extreme marginal tentacles of above a dozen rows. As the flattened
bases are thus formed of only a few rows of cells, the precision of the
movements of the tentacles is the more remarkable; for when the motor
impulse strikes the base of a tentacle in a very oblique direction
relatively to its broad face, scarcely more than one or two cells
towards one end can be affected at first, and the contraction of these
cells must draw the whole tentacle into the proper direction. It is,
perhaps, owing to the exterior pedicels being much flattened that they
do not bend quite so accurately to the point of excitement as the [page
247] more central ones. The properly directed movement of the tentacles
is not an unique case in the vegetable kingdom, for the tendrils of
many plants curve towards the side which is touched; but the case of
Drosera is far more interesting, as here the tentacles are not directly
excited, but receive an impulse from a distant point; nevertheless,
they bend accurately towards this point.

FIG. 11. (Drosera rotundifolia.) Diagram showing the distribution of
the vascular tissue in a small leaf.

On the Nature of the Tissues through which the Motor Impulse is
Transmitted.—It will be necessary first to describe briefly the course
of the main fibro-vascular bundles. These are shown in the accompanying
sketch (fig. 11) of a small leaf. Little vessels from the neighbouring
bundles enter all the many tentacles with which the surface is studded;
but these are not here represented. The central trunk, which runs up
the footstalk, bifurcates near the centre of the leaf, each branch
bifurcating again and again according to the size of the leaf. This
central trunk sends off, low down on each side, a delicate branch,
which may be called the sublateral branch. There is also, on each side,
a main lateral branch or bundle, which bifurcates in the same manner as
the others. Bifurcation does not imply that any single vessel divides,
but that a bundle [page 248] divides into two. By looking to either
side of the leaf, it will be seen that a branch from the great central
bifurcation inosculates with a branch from the lateral bundle, and that
there is a smaller inosculation between the two chief branches of the
lateral bundle. The course of the vessels is very complex at the larger
inosculation; and here vessels, retaining the same diameter, are often
formed by the union of the bluntly pointed ends of two vessels, but
whether these points open into each other by their attached surfaces, I
do not know. By means of the two inosculations all the vessels on the
same side of the leaf are brought into some sort of connection. Near
the circumference of the larger leaves the bifurcating branches also
come into close union, and then separate again, forming a continuous
zigzag line of vessels round the whole circumference. But the union of
the vessels in this zigzag line seems to be much less intimate than at
the main inosculation. It should be added that the course of the
vessels differs somewhat in different leaves, and even on opposite
sides of the same leaf, but the main inosculation is always present.

Now in my first experiments with bits of meat placed on one side of the
disc, it so happened that not a single tentacle was inflected on the
opposite side; and when I saw that the vessels on the same side were
all connected together by the two inosculations, whilst not a vessel
passed over to the opposite side, it seemed probable that the motor
impulse was conducted exclusively along them.

In order to test this view, I divided transversely with the point of a
lancet the central trunks of four leaves, just beneath the main
bifurcation; and two days afterwards placed rather large bits of raw
meat [page 249] (a most powerful stimulant) near the centre of the disc
above the incision—that is, a little towards the apex—with the
following results:—

[(1) This leaf proved rather torpid: after 4 hrs. 40 m. (in all cases
reckoning from the time when the meat was given) the tentacles at the
distal end were a little inflected, but nowhere else; they remained so
for three days, and re-expanded on the fourth day. The leaf was then
dissected, and the trunk, as well as the two sublateral branches, were
found divided.

(2) After 4 hrs. 30 m. many of the tentacles at the distal end were
well inflected. Next day the blade and all the tentacles at this end
were strongly inflected, and were separated by a distinct transverse
line from the basal half of the leaf, which was not in the least
affected. On the third day, however, some of the short tentacles on the
disc near the base were very slightly inflected. The incision was found
on dissection to extend across the leaf as in the last case.

(3) After 4 hrs. 30 m. strong inflection of the tentacles at the distal
end, which during the next two days never extended in the least to the
basal end. The incision as before.

(4) This leaf was not observed until 15 hrs. had elapsed, and then all
the tentacles, except the extreme marginal ones, were found equally
well inflected all round the leaf. On careful examination the spiral
vessels of the central trunk were certainly divided; but the incision
on one side had not passed through the fibrous tissue surrounding these
vessels, though it had passed through the tissue on the other side.*]

The appearance presented by the leaves (2) and (3) was very curious,
and might be aptly compared with that of a man with his backbone broken
and lower extremities paralysed. Excepting that the line between the
two halves was here transverse instead of longitudinal, these leaves
were in the same state as some of those in the former experiments, with
bits of meat placed on one side of the disc. The case of leaf (4)

* M. Ziegler made similar experiments by cutting the spiral vessels of
Drosera intermedia(‘Comptes rendus,’ 1874, p. 1417), but arrived at
conclusions widely different from mine. [page 250]


proves that the spiral vessels of the central trunk may be divided, and
yet the motor impulse be transmitted from the distal to the basal end;
and this led me at first to suppose that the motor force was sent
through the closely surrounding fibrous tissue; and that if one half of
this tissue was left undivided, it sufficed for complete transmission.
But opposed to this conclusion is the fact that no vessels pass
directly from one side of the leaf to the other, and yet, as we have
seen, if a rather large bit of meat is placed on one side, the motor
impulse is sent, though slowly and imperfectly, in a transverse
direction across the whole breadth of the leaf. Nor can this latter
fact be accounted for by supposing that the transmission is effected
through the two inosculations, or through the circumferential zigzag
line of union, for had this been the case, the exterior tentacles on
the opposite side of the disc would have been affected before the more
central ones, which never occurred. We have also seen that the extreme
marginal tentacles appear to have no power to transmit an impulse to
the adjoining tentacles; yet the little bundle of vessels which enters
each marginal tentacle sends off a minute branch to those on both
sides, and this I have not observed in any other tentacles; so that the
marginal ones are more closely connected together by spiral vessels
than are the others, and yet have much less power of communicating a
motor impulse to one another.

But besides these several facts and arguments we have conclusive
evidence that the motor impulse is not sent, at least exclusively,
through the spiral vessels, or through the tissue immediately
surrounding them. We know that if a bit of meat is placed on a gland
(the immediately adjoining ones having been removed) on any part of the
disc, all the short sur- [page 251] rounding tentacles bend almost
simultaneously with great precision towards it. Now there are tentacles
on the disc, for instance near the extremities of the sublateral
bundles (fig. 11), which are supplied with vessels that do not come
into contact with the branches that enter the surrounding tentacles,
except by a very long and extremely circuitous course. Nevertheless, if
a bit of meat is placed on the gland of a tentacle of this kind, all
the surrounding ones are inflected towards it with great precision. It
is, of course, possible that an impulse might be sent through a long
and circuitous course, but it is obviously impossible that the
direction of the movement could be thus communicated, so that all the
surrounding tentacles should bend precisely to the point of excitement.
The impulse no doubt is transmitted in straight radiating lines from
the excited gland to the surrounding tentacles; it cannot, therefore,
be sent along the fibro-vascular bundles. The effect of cutting the
central vessels, in the above cases, in preventing the transmission of
the motor impulse from the distal to the basal end of a leaf, may be
attributed to a considerable space of the cellular tissue having been
divided. We shall hereafter see, when we treat of Dionaea, that this
same conclusion, namely that the motor impulse is not transmitted by
the fibro-vascular bundles, is plainly confirmed; and Prof. Cohn has
come to the same conclusion with respect to Aldrovanda—both members of
the Droseraceae.

As the motor impulse is not transmitted along the vessels, there
remains for its passage only the cellular tissue; and the structure of
this tissue explains to a certain extent how it travels so quickly down
the long exterior tentacles, and much more slowly across the blade of
the leaf. We shall also see why it crosses [page 252] the blade more
quickly in a longitudinal than in a transverse direction; though with
time it can pass in any direction. We know that the same stimulus
causes movement of the tentacles and aggregation of the protoplasm, and
that both influences originate in and proceed from the glands within
the same brief space of time. It seems therefore probable that the
motor impulse consists of the first commencement of a molecular change
in the protoplasm, which, when well developed, is plainly visible, and
has been designated aggregation; but to this subject I shall return. We
further know that in the transmission of the aggregating process the
chief delay is caused by the passage of the transverse cell-walls; for
as the aggregation travels down the tentacles, the contents of each
successive cell seem almost to flash into a cloudy mass. We may
therefore infer that the motor impulse is in like manner delayed
chiefly by passing through the cell-walls.

The greater celerity with which the impulse is transmitted down the
long exterior tentacles than across the disc may be largely attributed
to its being closely confined within the narrow pedicel, instead of
radiating forth on all sides as on the disc. But besides this
confinement, the exterior cells of the tentacles are fully twice as
long as those of the disc; so that only half the number of transverse
partitions have to be traversed in a given length of a tentacle,
compared with an equal space on the disc; and there would be in the
same proportion less retardation of the impulse. Moreover, in sections
of the exterior tentacles given by Dr. Warming,* the parenchymatous

* ‘Videnskabelige Meddelelser de la Soc. d’Hist. nat. de Copenhague,’
Nos. 10-12, 1872, woodcuts iv. and v. [page 253]


cells are shown to be still more elongated; and these would form the
most direct line of communication from the gland to the bending place
of the tentacle. If the impulse travels down the exterior cells, it
would have to cross from between twenty to thirty transverse
partitions; but rather fewer if down the inner parenchymatous tissue.
In either case it is remarkable that the impulse is able to pass
through so many partitions down nearly the whole length of the pedicel,
and to act on the bending place, in ten seconds. Why the impulse, after
having passed so quickly down one of the extreme marginal tentacles
(about 1/20 of an inch in length), should never, as far as I have seen,
affect the adjoining tentacles, I do not understand. It may be in part
accounted for by much energy being expended in the rapidity of the
transmission.

Most of the cells of the disc, both the superficial ones and the larger
cells which form the five or six underlying layers, are about four
times as long as broad. They are arranged almost longitudinally,
radiating from the footstalk. The motor impulse, therefore, when
transmitted across the disc, has to cross nearly four times as many
cell-walls as when transmitted in a longitudinal direction, and would
consequently be much delayed in the former case. The cells of the disc
converge towards the bases of the tentacles, and are thus fitted to
convey the motor impulse to them from all sides. On the whole, the
arrangement and shape of the cells, both those of the disc and
tentacles, throw much light on the rate and manner of diffusion of the
motor impulse. But why the impulse proceeding from the glands of the
exterior rows of tentacles tends to travel laterally and towards the
centre of the leaf, but not centrifugally, is by no means clear. [page
254]

Mechanism of the Movements, and Nature of the Motor Impulse.—Whatever
may be the means of movement, the exterior tentacles, considering their
delicacy, are inflected with much force. A bristle, held so that a
length of 1 inch projected from a handle, yielded when I tried to lift
with it an inflected tentacle, which was somewhat thinner than the
bristle. The amount or extent, also, of the movement is great. Fully
expanded tentacles in becoming inflected sweep through an angle of
180o; and if they are beforehand reflexed, as often occurs, the angle
is considerably greater. It is probably the superficial cells at the
bending place which chiefly or exclusively contract; for the interior
cells have very delicate walls, and are so few in number that they
could hardly cause a tentacle to bend with precision to a definite
point. Though I carefully looked, I could never detect any wrinkling of
the surface at the bending place, even in the case of a tentacle
abnormally curved into a complete circle, under circumstances hereafter
to be mentioned.

All the cells are not acted on, though the motor impulse passes through
them. When the gland of one of the long exterior tentacles is excited,
the upper cells are not in the least affected; about halfway down there
is a slight bending, but the chief movement is confined to a short
space near the base; and no part of the inner tentacles bends except
the basal portion. With respect to the blade of the leaf, the motor
impulse may be transmitted through many cells, from the centre to the
circumference, without their being in the least affected, or they may
be strongly acted on and the blade greatly inflected. In the latter
case the movement seems to depend partly on the strength of the
stimulus, and partly on [page 255] its nature, as when leaves are
immersed in certain fluids.

The power of movement which various plants possess, when irritated, has
been attributed by high authorities to the rapid passage of fluid out
of certain cells, which, from their previous state of tension,
immediately contract.* Whether or not this is the primary cause of such
movements, fluid must pass out of closed cells when they contract or
are pressed together in one direction, unless they at the same time
expand in some other direction. For instance, fluid can be seen to ooze
from the surface of any young and vigorous shoot if slowly bent into a
semi-circle.** In the case of Drosera there is certainly much movement
of the fluid throughout the tentacles whilst they are undergoing
inflection. Many leaves can be found in which the purple fluid within
the cells is of an equally dark tint on the upper and lower sides of
the tentacles, extending also downwards on both sides to equally near
their bases. If the tentacles of such a leaf are excited into movement,
it will generally be found after some hours that the cells on the
concave side are much paler than they were before, or are quite
colourless, those on the convex side having become much darker. In two
instances, after particles of hair had been placed on glands, and when
in the course of 1 hr. 10 m. the tentacles were incurved halfway
towards the centre of the leaf, this change of colour in the two sides
was conspicuously plain. In another case, after a bit of meat had been
placed on a gland, the purple colour was observed at intervals to be
slowly travelling from the upper to the lower part, down the convex
side of

* Sachs, ‘Traité de Bot.’ 3rd edit. 1874, p. 1038. This view was, I
believe, first suggested by Lamarck.


** Sachs, ibid. p. 919. [page 256]


the bending tentacle. But it does not follow from these observations
that the cells on the convex side become filled with more fluid during
the act of inflection than they contained before; for fluid may all the
time be passing into the disc or into the glands which then secrete
freely.

The bending of the tentacles, when leaves are immersed in a dense
fluid, and their subsequent re-expansion in a less dense fluid, show
that the passage of fluid from or into the cells can cause movements
like the natural ones. But the inflection thus caused is often
irregular; the exterior tentacles being sometimes spirally curved.
Other unnatural movements are likewise caused by the application of
dense fluids, as in the case of drops of syrup placed on the backs of
leaves and tentacles. Such movements may be compared with the
contortions which many vegetable tissues undergo when subjected to
exosmose. It is therefore doubtful whether they throw any light on the
natural movements.

If we admit that the outward passage of fluid is the cause of the
bending of the tentacles, we must suppose that the cells, before the
act of inflection, are in a high state of tension, and that they are
elastic to an extraordinary degree; for otherwise their contraction
could not cause the tentacles often to sweep through an angle of above
180o. Prof. Cohn, in his interesting paper* on the movements of the
stamens of certain Compositae, states that these organs, when dead, are
as elastic as threads of india-rubber, and are then only half as long
as they were when alive. He believes that the living protoplasm

* ‘Abhand. der Schles. Gesell. fr vaterl. Cultur,’ 1861, Heft i. An
excellent abstract of this paper is given in the ‘Annals and Mag. of
Nat. Hist.’ 3rd series, 1863, vol. xi. pp. 188-197. [page 257]


within their cells is ordinarily in a state of expansion, but is
paralysed by irritation, or may be said to suffer temporary death; the
elasticity of the cell-walls then coming into play, and causing the
contraction of the stamens. Now the cells on the upper or concave side
of the bending part of the tentacles of Drosera do not appear to be in
a state of tension, nor to be highly elastic; for when a leaf is
suddenly killed, or dies slowly, it is not the upper but the lower
sides of the tentacles which contract from elasticity. We may,
therefore, conclude that their movements cannot be accounted for by the
inherent elasticity of certain cells, opposed as long as they are alive
and not irritated by the expanded state of their contents.

A somewhat different view has been advanced by other
physiologists—namely that the protoplasm, when irritated, contracts
like the soft sarcode of the muscles of animals. In Drosera the fluid
within the cells of the tentacles at the bending place appears under
the microscope thin and homogeneous, and after aggregation consists of
small, soft masses of matter, undergoing incessant changes of form and
floating in almost colourless fluid. These masses are completely
redissolved when the tentacles re-expand. Now it seems scarcely
possible that such matter should have any direct mechanical power; but
if through some molecular change it were to occupy less space than it
did before, no doubt the cell-walls would close up and contract. But in
this case it might be expected that the walls would exhibit wrinkles,
and none could ever be seen. Moreover, the contents of all the cells
seem to be of exactly the same nature, both before and after
aggregation; and yet only a few of the basal cells contract, the rest
of the tentacle remaining straight.

A third view maintained by some physiologists, [page 258] though
rejected by most others, is that the whole cell, including the walls,
actively contracts. If the walls are composed solely of non-nitrogenous
cellulose, this view is highly improbable; but it can hardly be doubted
that they must be permeated by proteid matter, at least whilst they are
growing. Nor does there seem any inherent improbability in the
cell-walls of Drosera contracting, considering their high state of
organisation; as shown in the case of the glands by their power of
absorption and secretion, and by being exquisitely sensitive so as to
be affected by the pressure of the most minute particles. The
cell-walls of the pedicels also allow various impulses to pass through
them, inducing movement, increased secretion and aggregation. On the
whole the belief that the walls of certain cells contract, some of
their contained fluid being at the same time forced outwards, perhaps
accords best with the observed facts. If this view is rejected, the
next most probable one is that the fluid contents of the cells shrink,
owing to a change in their molecular state, with the consequent closing
in of the walls. Anyhow, the movement can hardly be attributed to the
elasticity of the walls, together with a previous state of tension.

With respect to the nature of the motor impulse which is transmitted
from the glands down the pedicels and across the disc, it seems not
improbable that it is closely allied to that influence which causes the
protoplasm within the cells of the glands and tentacles to aggregate.
We have seen that both forces originate in and proceed from the glands
within a few seconds of the same time, and are excited by the same
causes. The aggregation of the protoplasm lasts almost as long as the
tentacles remain inflected, even though this be for more than a week;
but the [page 259] protoplasm is redissolved at the bending place
shortly before the tentacles re-expand, showing that the exciting cause
of the aggregating process has then quite ceased. Exposure to carbonic
acid causes both the latter process and the motor impulse to travel
very slowly down the tentacles. We know that the aggregating process is
delayed in passing through the cell- walls, and we have good reason to
believe that this holds good with the motor impulse; for we can thus
understand the different rates of its transmission in a longitudinal
and transverse line across the disc. Under a high power the first sign
of aggregation is the appearance of a cloud, and soon afterwards of
extremely fine granules, in the homogeneous purple fluid within the
cells; and this apparently is due to the union of molecules of
protoplasm. Now it does not seem an improbable view that the same
tendency—namely for the molecules to approach each other—should be
communicated to the inner surfaces of the cell-walls which are in
contact with the protoplasm; and if so, their molecules would approach
each other, and the cell-wall would contract.

To this view it may with truth be objected that when leaves are
immersed in various strong solutions, or are subjected to a heat of
above 130° Fahr. (54°.4 Cent.), aggregation ensues, but there is no
movement. Again, various acids and some other fluids cause rapid
movement, but no aggregation, or only of an abnormal nature, or only
after a long interval of time; but as most of these fluids are more or
less injurious, they may check or prevent the aggregating process by
injuring or killing the protoplasm. There is another and more important
difference in the two processes: when the glands on the disc are
excited, they transmit some influence up the surrounding [page 260]
tentacles, which acts on the cells at the bending place, but does not
induce aggregation until it has reached the glands; these then send
back some other influence, causing the protoplasm to aggregate, first
in the upper and then in the lower cells.

The Re-expansion of the Tentacles.—This movement is always slow and
gradual. When the centre of the leaf is excited, or a leaf is immersed
in a proper solution, all the tentacles bend directly towards the
centre, and afterwards directly back from it. But when the point of
excitement is on one side of the disc, the surrounding tentacles bend
towards it, and therefore obliquely with respect to their normal
direction; when they afterwards re-expand, they bend obliquely back, so
as to recover their original positions. The tentacles farthest from an
excited point, wherever that may be, are the last and the least
affected, and probably in consequence of this they are the first to
re-expand. The bent portion of a closely inflected tentacle is in a
state of active contraction, as shown by the following experiment. Meat
was placed on a leaf, and after the tentacles were closely inflected
and had quite ceased to move, narrow strips of the disc, with a few of
the outer tentacles attached to it, were cut off and laid on one side
under the microscope. After several failures, I succeeded in cutting
off the convex surface of the bent portion of a tentacle. Movement
immediately recommenced, and the already greatly bent portion went on
bending until it formed a perfect circle; the straight distal portion
of the tentacle passing on one side of the strip. The convex surface
must therefore have previously been in a state of tension, sufficient
to counter-balance that of the concave surface, which, when free,
curled into a complete ring.

The tentacles of an expanded and unexcited leaf [page 261] are
moderately rigid and elastic; if bent by a needle, the upper end yields
more easily than the basal and thicker part, which alone is capable of
becoming inflected. The rigidity of this basal part seems due to the
tension of the outer surface balancing a state of active and persistent
contraction of the cells of the inner surface. I believe that this is
the case, because, when a leaf is dipped into boiling water, the
tentacles suddenly become reflexed, and this apparently indicates that
the tension of the outer surface is mechanical, whilst that of the
inner surface is vital, and is instantly destroyed by the boiling
water. We can thus also understand why the tentacles as they grow old
and feeble slowly become much reflexed. If a leaf with its tentacles
closely inflected is dipped into boiling water, these rise up a little,
but by no means fully re-expand. This may be owing to the heat quickly
destroying the tension and elasticity of the cells of the convex
surface; but I can hardly believe that their tension, at any one time,
would suffice to carry back the tentacles to their original position,
often through an angle of above 180o. It is more probable that fluid,
which we know travels along the tentacles during the act of inflection,
is slowly re-attracted into the cells of the convex surface, their
tension being thus gradually and continually increased.

A recapitulation of the chief facts and discussions in this chapter
will be given at the close of the next chapter. [page 262]




CHAPTER XI.
RECAPITULATION OF THE CHIEF OBSERVATIONS ON DROSERA ROTUNDIFOLIA.


As summaries have been given to most of the chapters, it will be
sufficient here to recapitulate, as briefly as I can, the chief points.
In the first chapter a preliminary sketch was given of the structure of
the leaves, and of the manner in which they capture insects. This is
effected by drops of extremely viscid fluid surrounding the glands and
by the inward movement of the tentacles. As the plants gain most of
their nutriment by this means, their roots are very poorly developed;
and they often grow in places where hardly any other plant except
mosses can exist. The glands have the power of absorption, besides that
of secretion. They are extremely sensitive to various stimulants,
namely repeated touches, the pressure of minute particles, the
absorption of animal matter and of various fluids, heat, and galvanic
action. A tentacle with a bit of raw meat on the gland has been seen to
begin bending in 10 s., to be strongly incurved in 5 m., and to reach
the centre of the leaf in half an hour. The blade of the leaf often
becomes so much inflected that it forms a cup, enclosing any object
placed on it.

A gland, when excited, not only sends some influence down its own
tentacle, causing it to bend, but likewise to the surrounding
tentacles, which become incurved; so that the bending place can be
acted on by an impulse received from opposite directions, [page 263]
namely from the gland on the summit of the same tentacle, and from one
or more glands of the neighbouring tentacles. Tentacles, when
inflected, re-expand after a time, and during this process the glands
secrete less copiously, or become dry. As soon as they begin to secrete
again, the tentacles are ready to re-act; and this may be repeated at
least three, probably many more times.

It was shown in the second chapter that animal substances placed on the
discs cause much more prompt and energetic inflection than do inorganic
bodies of the same size, or mere mechanical irritation; but there is a
still more marked difference in the greater length of time during which
the tentacles remain inflected over bodies yielding soluble and
nutritious matter, than over those which do not yield such matter.
Extremely minute particles of glass, cinders, hair, thread,
precipitated chalk, &c., when placed on the glands of the outer
tentacles, cause them to bend. A particle, unless it sinks through the
secretion and actually touches the surface of the gland with some one
point, does not produce any effect. A little bit of thin human hair
8/1000 of an inch (.203 mm.) in length, and weighing only 1/78740 of a
grain (.000822 mg.), though largely supported by the dense secretion,
suffices to induce movement. It is not probable that the pressure in
this case could have amounted to that from the millionth of a grain.
Even smaller particles cause a slight movement, as could be seen
through a lens. Larger particles than those of which the measurements
have been given cause no sensation when placed on the tongue, one of
the most sensitive parts of the human body.

Movement ensues if a gland is momentarily touched three or four times;
but if touched only once or twice, [page 264] though with considerable
force and with a hard object, the tentacle does not bend. The plant is
thus saved from much useless movement, as during a high wind the glands
can hardly escape being occasionally brushed by the leaves of
surrounding plants. Though insensible to a single touch, they are
exquisitely sensitive, as just stated, to the slightest pressure if
prolonged for a few seconds; and this capacity is manifestly of service
to the plant in capturing small insects. Even gnats, if they rest on
the glands with their delicate feet, are quickly and securely embraced.
The glands are insensible to the weight and repeated blows of drops of
heavy rain, and the plants are thus likewise saved from much useless
movement.

The description of the movements of the tentacles was interrupted in
the third chapter for the sake of describing the process of
aggregation. This process always commences in the cells of the glands,
the contents of which first become cloudy; and this has been observed
within 10 s. after a gland has been excited. Granules just resolvable
under a very high power soon appear, sometimes within a minute, in the
cells beneath the glands; and these then aggregate into minute spheres.
The process afterwards travels down the tentacles, being arrested for a
short time at each transverse partition. The small spheres coalesce
into larger spheres, or into oval, club-headed, thread- or
necklace-like, or otherwise shaped masses of protoplasm, which,
suspended in almost colourless fluid, exhibit incessant spontaneous
changes of form. These frequently coalesce and again separate. If a
gland has been powerfully excited, all the cells down to the base of
the tentacle are affected. In cells, especially if filled with dark red
fluid, the first step in the [page 265] process often is the formation
of a dark red, bag-like mass of protoplasm, which afterwards divides
and undergoes the usual repeated changes of form. Before any
aggregation has been excited, a sheet of colourless protoplasm,
including granules (the primordial utricle of Mohl), flows round the
walls of the cells; and this becomes more distinct after the contents
have been partially aggregated into spheres or bag-like masses. But
after a time the granules are drawn towards the central masses and
unite with them; and then the circulating sheet can no longer be
distinguished, but there is still a current of transparent fluid within
the cells.

Aggregation is excited by almost all the stimulants which induce
movement; such as the glands being touched two or three times, the
pressure of minute inorganic particles, the absorption of various
fluids, even long immersion in distilled water, exosmose, and heat. Of
the many stimulants tried, carbonate of ammonia is the most energetic
and acts the quickest: a dose of 1/134400 of a grain (.00048 mg.) given
to a single gland suffices to cause in one hour well-marked aggregation
in the upper cells of the tentacle. The process goes on only as long as
the protoplasm is in a living, vigorous, and oxygenated condition.

The result is in all respects exactly the same, whether a gland has
been excited directly, or has received an influence from other and
distant glands. But there is one important difference: when the central
glands are irritated, they transmit centrifugally an influence up the
pedicels of the exterior tentacles to their glands; but the actual
process of aggregation travels centripetally, from the glands of the
exterior tentacles down their pedicels. The exciting influence,
therefore, which is transmitted from [page 266] one part of the leaf to
another must be different from that which actually induces aggregation.
The process does not depend on the glands secreting more copiously than
they did before; and is independent of the inflection of the tentacles.
It continues as long as the tentacles remain inflected, and as soon as
these are fully re-expanded, the little masses of protoplasm are all
redissolved; the cells becoming filled with homogeneous purple fluid,
as they were before the leaf was excited.

As the process of aggregation can be excited by a few touches, or by
the pressure of insoluble particles, it is evidently independent of the
absorption of any matter, and must be of a molecular nature. Even when
caused by the absorption of the carbonate or other salt of ammonia, or
an infusion of meat, the process seems to be of exactly the same
nature. The protoplasmic fluid must, therefore, be in a singularly
unstable condition, to be acted on by such slight and varied causes.
Physiologists believe that when a nerve is touched, and it transmits an
influence to other parts of the nervous system, a molecular change is
induced in it, though not visible to us. Therefore it is a very
interesting spectacle to watch the effects on the cells of a gland, of
the pressure of a bit of hair, weighing only 1/78700 of a grain and
largely supported by the dense secretion, for this excessively slight
pressure soon causes a visible change in the protoplasm, which change
is transmitted down the whole length of the tentacle, giving it at last
a mottled appearance, distinguishable even by the naked eye.

In the fourth chapter it was shown that leaves placed for a short time
in water at a temperature of 110° Fahr. (43°.3 Cent.) become somewhat
inflected; they are thus also rendered more sensitive to the action
[page 267] of meat than they were before. If exposed to a temperature
of between 115° and 125°(46°.1-51°.6 Cent.), they are quickly
inflected, and their protoplasm undergoes aggregation; when afterwards
placed in cold water, they re-expand. Exposed to 130° (54°.4 Cent.), no
inflection immediately occurs, but the leaves are only temporarily
paralysed, for on being left in cold water, they often become inflected
and afterwards re-expand. In one leaf thus treated, I distinctly saw
the protoplasm in movement. In other leaves, treated in the same
manner, and then immersed in a solution of carbonate of ammonia, strong
aggregation ensued. Leaves placed in cold water, after an exposure to
so high a temperature as 145° (62°.7 Cent.), sometimes become slightly,
though slowly, inflected; and afterwards have the contents of their
cells strongly aggregated by carbonate of ammonia. But the duration of
the immersion is an important element, for if left in water at 145°
(62°.7 Cent.), or only at 140° (60° Cent.), until it becomes cool, they
are killed, and the contents of the glands are rendered white and
opaque. This latter result seems to be due to the coagulation of the
albumen, and was almost always caused by even a short exposure to 150°
(65.5 Cent.); but different leaves, and even the separate cells in the
same tentacle, differ considerably in their power of resisting heat.
Unless the heat has been sufficient to coagulate the albumen, carbonate
of ammonia subsequently induces aggregation.

In the fifth chapter, the results of placing drops of various
nitrogenous and non-nitrogenous organic fluids on the discs of leaves
were given, and it was shown that they detect with almost unerring
certainty the presence of nitrogen. A decoction of green peas or of
fresh cabbage-leaves acts almost as powerfully as an infusion of raw
meat; whereas an infusion of cabbage- [page 268] leaves made by keeping
them for a long time in merely warm water is far less efficient. A
decoction of grass-leaves is less powerful than one of green peas or
cabbage-leaves.

These results led me to inquire whether Drosera possessed the power of
dissolving solid animal matter. The experiments proving that the leaves
are capable of true digestion, and that the glands absorb the digested
matter, are given in detail in the sixth chapter. These are, perhaps,
the most interesting of all my observations on Drosera, as no such
power was before distinctly known to exist in the vegetable kingdom. It
is likewise an interesting fact that the glands of the disc, when
irritated, should transmit some influence to the glands of the exterior
tentacles, causing them to secrete more copiously and the secretion to
become acid, as if they had been directly excited by an object placed
on them. The gastric juice of animals contains, as is well known, an
acid and a ferment, both of which are indispensable for digestion, and
so it is with the secretion of Drosera. When the stomach of an animal
is mechanically irritated, it secretes an acid, and when particles of
glass or other such objects were placed on the glands of Drosera, the
secretion, and that of the surrounding and untouched glands, was
increased in quantity and became acid. But, according to Schiff, the
stomach of an animal does not secrete its proper ferment, pepsin, until
certain substances, which he calls peptogenes, are absorbed; and it
appears from my experiments that some matter must be absorbed by the
glands of Drosera before they secrete their proper ferment. That the
secretion does contain a ferment which acts only in the presence of an
acid on solid animal matter, was clearly proved by adding minute doses
of [page 269] an alkali, which entirely arrested the process of
digestion, this immediately recommencing as soon as the alkali was
neutralised by a little weak hydrochloric acid. From trials made with a
large number of substances, it was found that those which the secretion
of Drosera dissolves completely, or partially, or not at all, are acted
on in exactly the same manner by gastric juice. We may, therefore,
conclude that the ferment of Drosera is closely analogous to, or
identical with, the pepsin of animals.

The substances which are digested by Drosera act on the leaves very
differently. Some cause much more energetic and rapid inflection of the
tentacles, and keep them inflected for a much longer time, than do
others. We are thus led to believe that the former are more nutritious
than the latter, as is known to be the case with some of these same
substances when given to animals; for instance, meat in comparison with
gelatine. As cartilage is so tough a substance and is so little acted
on by water, its prompt dissolution by the secretion of Drosera, and
subsequent absorption is, perhaps, one of the most striking cases. But
it is not really more remarkable than the digestion of meat, which is
dissolved by this secretion in the same manner and by the same stages
as by gastric juice. The secretion dissolves bone, and even the enamel
of teeth, but this is simply due to the large quantity of acid
secreted, owing, apparently, to the desire of the plant for phosphorus.
In the case of bone, the ferment does not come into play until all the
phosphate of lime has been decomposed and free acid is present, and
then the fibrous basis is quickly dissolved. Lastly, the secretion
attacks and dissolves matter out of living seeds, which it sometimes
kills, or injures, as shown by the diseased state [page 270] of the
seedlings. It also absorbs matter from pollen, and from fragments of
leaves.

The seventh chapter was devoted to the action of the salts of ammonia.
These all cause the tentacles, and often the blade of the leaf, to be
inflected, and the protoplasm to be aggregated. They act with very
different power; the citrate being the least powerful, and the
phosphate, owing, no doubt, to the presence of phosphorus and nitrogen,
by far the most powerful. But the relative efficiency of only three
salts of ammonia was carefully determined, namely the carbonate,
nitrate, and phosphate. The experiments were made by placing
half-minims (.0296 ml.) of solutions of different strengths on the
discs of the leaves,—by applying a minute drop (about the 1/20 of a
minim, or .00296 ml.) for a few seconds to three or four glands,—and by
the immersion of whole leaves in a measured quantity. In relation to
these experiments it was necessary first to ascertain the effects of
distilled water, and it was found, as described in detail, that the
more sensitive leaves are affected by it, but only in a slight degree.

A solution of the carbonate is absorbed by the roots and induces
aggregation in their cells, but does not affect the leaves. The vapour
is absorbed by the glands, and causes inflection as well as
aggregation. A drop of a solution containing 1/960 of a grain (.0675
mg.) is the least quantity which, when placed on the glands of the
disc, excites the exterior tentacles to bend inwards. But a minute
drop, containing 1/14400 of a grain (.00445 mg.), if applied for a few
seconds to the secretion surrounding a gland, causes the inflection of
the same tentacle. When a highly sensitive leaf is immersed in a
solution, and there is ample time for absorption, the 1/268800 of a
grain [page 271] (.00024 mg.) is sufficient to excite a single tentacle
into movement.

The nitrate of ammonia induces aggregation of the protoplasm much less
quickly than the carbonate, but is more potent in causing inflection. A
drop containing 1/2400 of a grain (.027 mg.) placed on the disc acts
powerfully on all the exterior tentacles, which have not themselves
received any of the solution; whereas a drop with 1/2800 of a grain
caused only a few of these tentacles to bend, but affected rather more
plainly the blade. A minute drop applied as before, and containing
1/28800 of a grain (.0025 mg.), caused the tentacle bearing this gland
to bend. By the immersion of whole leaves, it was proved that the
absorption by a single gland of 1/691200 of a grain (.0000937 mg.) was
sufficient to set the same tentacle into movement.

The phosphate of ammonia is much more powerful than the nitrate. A drop
containing 1/3840 of a grain (.0169 mg.) placed on the disc of a
sensitive leaf causes most of the exterior tentacles to be inflected,
as well as the blade of the leaf. A minute drop containing 1/153600 of
a grain (.000423 mg.), applied for a few seconds to a gland, acts, as
shown by the movement of the tentacle. When a leaf is immersed in
thirty minims (1.7748 ml.) of a solution of one part by weight of the
salt to 21,875,000 of water, the absorption by a gland of only the
1/19760000 of a grain (.00000328 mg.), that is, about the
one-twenty-millionth of a grain, is sufficient to cause the tentacle
bearing this gland to bend to the centre of the leaf. In this
experiment, owing to the presence of the water of crystallisation, less
than the one-thirty-millionth of a grain of the efficient elements
could have been absorbed. There is nothing remarkable in such minute
quantities being absorbed by the glands, [page 272] for all
physiologists admit that the salts of ammonia, which must be brought in
still smaller quantity by a single shower of rain to the roots, are
absorbed by them. Nor is it surprising that Drosera should be enabled
to profit by the absorption of these salts, for yeast and other low
fungoid forms flourish in solutions of ammonia, if the other necessary
elements are present. But it is an astonishing fact, on which I will
not here again enlarge, that so inconceivably minute a quantity as the
one-twenty-millionth of a grain of phosphate of ammonia should induce
some change in a gland of Drosera, sufficient to cause a motor impulse
to be sent down the whole length of the tentacle; this impulse exciting
movement often through an angle of above 180o. I know not whether to be
most astonished at this fact, or that the pressure of a minute bit of
hair, supported by the dense secretion, should quickly cause
conspicuous movement. Moreover, this extreme sensitiveness, exceeding
that of the most delicate part of the human body, as well as the power
of transmitting various impulses from one part of the leaf to another,
have been acquired without the intervention of any nervous system.

As few plants are at present known to possess glands specially adapted
for absorption, it seemed worth while to try the effects on Drosera of
various other salts, besides those of ammonia, and of various acids.
Their action, as described in the eighth chapter, does not correspond
at all strictly with their chemical affinities, as inferred from the
classification commonly followed. The nature of the base is far more
influential than that of the acid; and this is known to hold good with
animals. For instance, nine salts of sodium all caused well-marked
inflection, and none of them were poisonous in small doses; whereas
seven of the nine corre- [page 273] sponding salts of potassium
produced no effect, two causing slight inflection. Small doses,
moreover, of some of the latter salts were poisonous. The salts of
sodium and potassium, when injected into the veins of animals, likewise
differ widely in their action. The so-called earthy salts produce
hardly any effect on Drosera. On the other hand, most of the metallic
salts cause rapid and strong inflection, and are highly poisonous; but
there are some odd exceptions to this rule; thus chloride of lead and
zinc, as well as two salts of barium, did not cause inflection, and
were not poisonous.

Most of the acids which were tried, though much diluted (one part to
437 of water), and given in small doses, acted powerfully on Drosera;
nineteen, out of the twenty-four, causing the tentacles to be more or
less inflected. Most of them, even the organic acids, are poisonous,
often highly so; and this is remarkable, as the juices of so many
plants contain acids. Benzoic acid, which is innocuous to animals,
seems to be as poisonous to Drosera as hydrocyanic. On the other hand,
hydrochloric acid is not poisonous either to animals or to Drosera, and
induces only a moderate amount of inflection. Many acids excite the
glands to secrete an extraordinary quantity of mucus; and the
protoplasm within their cells seems to be often killed, as may be
inferred from the surrounding fluid soon becoming pink. It is strange
that allied acids act very differently: formic acid induces very slight
inflection, and is not poisonous; whereas acetic acid of the same
strength acts most powerfully and is poisonous. Lactic acid is also
poisonous, but causes inflection only after a considerable lapse of
time. Malic acid acts slightly, whereas citric and tartaric acids
produce no effect. [page 274]

In the ninth chapter the effects of the absorption of various alkaloids
and certain other substances were described. Although some of these are
poisonous, yet as several, which act powerfully on the nervous system
of animals, produce no effect on Drosera, we may infer that the extreme
sensibility of the glands, and their power of transmitting an influence
to other parts of the leaf, causing movement, or modified secretion, or
aggregation, does not depend on the presence of a diffused element,
allied to nerve-tissue. One of the most remarkable facts is that long
immersion in the poison of the cobra-snake does not in the least check,
but rather stimulates, the spontaneous movements of the protoplasm in
the cells of the tentacles. Solutions of various salts and acids behave
very differently in delaying or in quite arresting the subsequent
action of a solution of phosphate of ammonia. Camphor dissolved in
water acts as a stimulant, as do small doses of certain essential oils,
for they cause rapid and strong inflection. Alcohol is not a stimulant.
The vapours of camphor, alcohol, chloroform, sulphuric and nitric
ether, are poisonous in moderately large doses, but in small doses
serve as narcotics or, anaesthetics, greatly delaying the subsequent
action of meat. But some of these vapours also act as stimulants,
exciting rapid, almost spasmodic movements in the tentacles. Carbonic
acid is likewise a narcotic, and retards the aggregation of the
protoplasm when carbonate of ammonia is subsequently given. The first
access of air to plants which have been immersed in this gas sometimes
acts as a stimulant and induces movement. But, as before remarked, a
special pharmacopoeia would be necessary to describe the diversified
effects of various substances on the leaves of Drosera.

In the tenth chapter it was shown that the sensitive- [page 275] ness
of the leaves appears to be wholly confined to the glands and to the
immediately underlying cells. It was further shown that the motor
impulse and other forces or influences, proceeding from the glands when
excited, pass through the cellular tissue, and not along the
fibro-vascular bundles. A gland sends its motor impulse with great
rapidity down the pedicel of the same tentacle to the basal part which
alone bends. The impulse, then passing onwards, spreads on all sides to
the surrounding tentacles, first affecting those which stand nearest
and then those farther off. But by being thus spread out, and from the
cells of the disc not being so much elongated as those of the
tentacles, it loses force, and here travels much more slowly than down
the pedicels. Owing also to the direction and form of the cells, it
passes with greater ease and celerity in a longitudinal than in a
transverse line across the disc. The impulse proceeding from the glands
of the extreme marginal tentacles does not seem to have force enough to
affect the adjoining tentacles; and this may be in part due to their
length. The impulse from the glands of the next few inner rows spreads
chiefly to the tentacles on each side and towards the centre of the
leaf; but that proceeding from the glands of the shorter tentacles on
the disc radiates almost equally on all sides.

When a gland is strongly excited by the quantity or quality of the
substance placed on it, the motor impulse travels farther than from one
slightly excited; and if several glands are simultaneously excited, the
impulses from all unite and spread still farther. As soon as a gland is
excited, it discharges an impulse which extends to a considerable
distance; but afterwards, whilst the gland is secreting and absorbing,
the impulse suffices only to keep the same tentacle [page 276]
inflected; though the inflection may last for many days.

If the bending place of a tentacle receives an impulse from its own
gland, the movement is always towards the centre of the leaf; and so it
is with all the tentacles, when their glands are excited by immersion
in a proper fluid. The short ones in the middle part of the disc must
be excepted, as these do not bend at all when thus excited. On the
other hand, when the motor impulse comes from one side of the disc, the
surrounding tentacles, including the short ones in the middle of the
disc, all bend with precision towards the point of excitement, wherever
this may be seated. This is in every way a remarkable phenomenon; for
the leaf falsely appears as if endowed with the senses of an animal. It
is all the more remarkable, as when the motor impulse strikes the base
of a tentacle obliquely with respect to its flattened surface, the
contraction of the cells must be confined to one, two, or a very few
rows at one end. And different sides of the surrounding tentacles must
be acted on, in order that all should bend with precision to the point
of excitement.

The motor impulse, as it spreads from one or more glands across the
disc, enters the bases of the surrounding tentacles, and immediately
acts on the bending place. It does not in the first place proceed up
the tentacles to the glands, exciting them to reflect back an impulse
to their bases. Nevertheless, some influence is sent up to the glands,
as their secretion is soon increased and rendered acid; and then the
glands, being thus excited, send back some other influence (not
dependent on increased secretion, nor on the inflection of the
tentacles), causing the protoplasm to aggregate in cell beneath cell.
This may [page 277] be called a reflex action, though probably very
different from that proceeding from the nerve-ganglion of an animal;
and it is the only known case of reflex action in the vegetable
kingdom.

About the mechanism of the movements and the nature of the motor
impulse we know very little. During the act of inflection fluid
certainly travels from one part to another of the tentacles. But the
hypothesis which agrees best with the observed facts is that the motor
impulse is allied in nature to the aggregating process; and that this
causes the molecules of the cell-walls to approach each other, in the
same manner as do the molecules of the protoplasm within the cells; so
that the cell-walls contract. But some strong objections may be urged
against this view. The re-expansion of the tentacles is largely due to
the elasticity of their outer cells, which comes into play as soon as
those on the inner side cease contracting with prepotent force; but we
have reason to suspect that fluid is continually and slowly attracted
into the outer cells during the act of re-expansion, thus increasing
their tension.

I have now given a brief recapitulation of the chief points observed by
me, with respect to the structure, movements, constitution, and habits
of Drosera rotundifolia; and we see how little has been made out in
comparison with what remains unexplained and unknown. [page 278]




CHAPTER XII.
ON THE STRUCTURE AND MOVEMENTS OF SOME OTHER SPECIES OF DROSERA.


Drosera anglica—Drosera intermedia—Drosera capensis—Drosera
spathulata—Drosera filiformis—Drosera binata—Concluding remarks.


I examined six other species of Drosera, some of them inhabitants of
distant countries, chiefly for the sake of ascertaining whether they
caught insects. This seemed the more necessary as the leaves of some of
the species differ to an extraordinary degree in shape from the rounded
ones of Drosera rotundifolia. In functional powers, however, they
differ very little.

[Drosera anglica (Hudson).*—The leaves of this species, which was sent
to me from Ireland, are much elongated, and gradually widen from the
footstalk to the bluntly pointed apex. They stand almost erect, and
their blades sometimes exceed 1 inch in length, whilst their breadth is
only the 1/5 of an inch. The glands of all the tentacles have the same
structure, so that the extreme marginal ones do not differ from the
others, as in the case of Drosera rotundifolia. When they are irritated
by being roughly touched, or by the pressure of minute inorganic
particles, or by contact with animal matter, or by the absorption of
carbonate of ammonia, the tentacles become inflected; the basal portion
being the chief seat of movement. Cutting or pricking the blade of the
leaf did not excite any movement. They frequently capture insects, and
the glands of the inflected tentacles pour forth much acid secretion.
Bits of roast meat were placed on some glands, and the tentacles began
to move in 1 m. or

* Mrs. Treat has given an excellent account in ‘The American
Naturalist,’ December 1873, p. 705, of Drosera longifolia (which is a
synonym in part of Drosera anglica), of Drosera rotundifolia and
filiformis. [page 279]


1 m. 30 s.; and in 1 hr. 10 m. reached the centre. Two bits of boiled
cork, one of boiled thread, and two of coal-cinders taken from the
fire, were placed, by the aid of an instrument which had been immersed
in boiling water, on five glands; these superfluous precautions having
been taken on account of M. Ziegler’s statements. One of the particles
of cinder caused some inflection in 8 hrs. 45 m., as did after 23 hrs.
the other particle of cinder, the bit of thread, and both bits of cork.
Three glands were touched half a dozen times with a needle; one of the
tentacles became well inflected in 17 m., and re-expanded after 24
hrs.; the two others never moved. The homogeneous fluid within the
cells of the tentacles undergoes aggregation after these have become
inflected; especially if given a solution of carbonate of ammonia; and
I observed the usual movements in the masses of protoplasm. In one
case, aggregation ensued in 1 hr. 10 m. after a tentacle had carried a
bit of meat to the centre. From these facts it is clear that the
tentacles of Drosera anglica behave like those of Drosera rotundifolia.

If an insect is placed on the central glands, or has been naturally
caught there, the apex of the leaf curls inwards. For instance, dead
flies were placed on three leaves near their bases, and after 24 hrs.
the previously straight apices were curled completely over, so as to
embrace and conceal the flies; they had therefore moved through an
angle of 180o. After three days the apex of one leaf, together with the
tentacles, began to re-expand. But as far as I have seen— and I made
many trials—the sides of the leaf are never inflected, and this is the
one functional difference between this species and Drosera
rotundifolia.

Drosera intermedia (Hayne).—This species is quite as common in some
parts of England as Drosera rotundifolia. It differs from Drosera
anglica, as far as the leaves are concerned, only in their smaller
size, and in their tips being generally a little reflexed. They capture
a large number of insects. The tentacles are excited into movement by
all the causes above specified; and aggregation ensues, with movement
of the protoplasmic masses. I have seen, through a lens, a tentacle
beginning to bend in less than a minute after a particle of raw meat
had been placed on the gland. The apex of the leaf curls over an
exciting object as in the case of Drosera anglica. Acid secretion is
copiously poured over captured insects. A leaf which had embraced a fly
with all its tentacles re-expanded after nearly three days.

Drosera capensis.—This species, a native of the Cape of Good Hope, was
sent to me by Dr. Hooker. The leaves are elongated, slightly concave
along the middle and taper towards the apex, [page 280] which is
bluntly pointed and reflexed. They rise from an almost woody axis, and
their greatest peculiarity consists in their foliaceous green
footstalks, which are almost as broad and even longer than the
gland-bearing blade. This species, therefore, probably draws more
nourishment from the air, and less from captured insects, than the
other species of the genus. Nevertheless, the tentacles are crowded
together on the disc, and are extremely numerous; those on the margins
being much longer than the central ones. All the glands have the same
form; their secretion is extremely viscid and acid.

The specimen which I examined had only just recovered from a weak state
of health. This may account for the tentacles moving very slowly when
particles of meat were placed on the glands, and perhaps for my never
succeeding in causing any movement by repeatedly touching them with a
needle. But with all the species of the genus this latter stimulus is
the least effective of any. Particles of glass, cork, and coal-cinders,
were placed on the glands of six tentacles; and one alone moved after
an interval of 2 hrs. 30 m. Nevertheless, two glands were extremely
sensitive to very small doses of the nitrate of ammonia, namely to
about 1/20 of a minim of a solution (one part to 5250 of water),
containing only 1/115200 of a grain (.000562 mg.) of the salt.
Fragments of flies were placed on two leaves near their tips, which
became incurved in 15 hrs. A fly was also placed in the middle of the
leaf; in a few hours the tentacles on each side embraced it, and in 8
hrs. the whole leaf directly beneath the fly was a little bent
transversely. By the next morning, after 23 hrs., the leaf was curled
so completely over that the apex rested on the upper end of the
footstalk. In no case did the sides of the leaves become inflected. A
crushed fly was placed on the foliaceous footstalk, but produced no
effect.

Drosera spathulata (sent to me by Dr. Hooker).—I made only a few
observations on this Australian species, which has long, narrow leaves,
gradually widening towards their tips. The glands of the extreme
marginal tentacles are elongated and differ from the others, as in the
case of Drosera rotundifolia. A fly was placed on a leaf, and in 18
hrs. it was embraced by the adjoining tentacles. Gum-water dropped on
several leaves produced no effect. A fragment of a leaf was immersed in
a few drops of a solution of one part of carbonate of ammonia to 146 of
water; all the glands were instantly blackened; the process of
aggregation could be seen travelling rapidly down the cells of the
tentacles; and the granules of protoplasm soon united into spheres and
variously shaped masses, which displayed the usual move- [page 281]
ments. Half a minim of a solution of one part of nitrate of ammonia to
146 of water was next placed on the centre of a leaf; after 6 hrs. some
marginal tentacles on both sides were inflected, and after 9 hrs. they
met in the centre. The lateral edges of the leaf also became incurved,
so that it formed a half-cylinder; but the apex of the leaf in none of
my few trials was inflected. The above dose of the nitrate (viz. 1/320
of a grain, or .202 mg.) was too powerful, for in the course of 23 hrs.
the leaf died.

Drosera filiformis.—This North American species grows in such abundance
in parts of New Jersey as almost to cover the ground. It catches,
according to Mrs. Treat,* an extraordinary number of small and large
insects, even great flies of the genus Asilus, moths, and butterflies.
The specimen which I examined, sent me by Dr. Hooker, had thread-like
leaves, from 6 to 12 inches in length, with the upper surface convex
and the lower flat and slightly channelled. The whole convex surface,
down to the roots—for there is no distinct footstalk—is covered with
short gland-bearing tentacles, those on the margins being the longest
and reflexed. Bits of meat placed on the glands of some tentacles
caused them to be slightly inflected in 20 m.; but the plant was not in
a vigorous state. After 6 hrs. they moved through an angle of 90o, and
in 24 hrs. reached the centre. The surrounding tentacles by this time
began to curve inwards. Ultimately a large drop of extremely viscid,
slightly acid secretion was poured over the meat from the united
glands. Several other glands were touched with a little saliva, and the
tentacles became incurved in under 1 hr., and re-expanded after 18 hrs.
Particles of glass, cork, cinders, thread, and gold-leaf, were placed
on numerous glands on two leaves; in about 1 hr. four tentacles became
curved, and four others after an additional interval of 2 hrs. 30 m. I
never once succeeded in causing any movement by repeatedly touching the
glands with a needle; and Mrs. Treat made similar trials for me with no
success. Small flies were placed on several leaves near their tips, but
the thread-like blade became only on one occasion very slightly bent,
directly beneath the insect. Perhaps this indicates that the blades of
vigorous plants would bend over captured insects, and Dr. Canby informs
me that this is the case; but the movement cannot be strongly
pronounced, as it was not observed by Mrs. Treat.

Drosera binata (or dichotoma).—I am much indebted to Lady

* ‘American Naturalist,’ December 1873, page 705. [page 282]


Dorothy Nevill for a fine plant of this almost gigantic Australian
species, which differs in some interesting points from those previously
described. In this specimen the rush-like footstalks of the leaves were
20 inches in length. The blade bifurcates at its junction with the
footstalk, and twice or thrice afterwards, curling about in an
irregular manner. It is narrow, being only 3/20 of an inch in breadth.
One blade was 7 1/2 inches long, so that the entire leaf, including the
footstalk, was above 27 inches in length. Both surfaces are slightly
hollowed out. The upper surface is covered with tentacles arranged in
alternate rows; those in the middle being short and crowded together,
those towards the margins longer, even twice or thrice as long as the
blade is broad. The glands of the exterior tentacles are of a much
darker red than those of the central ones. The pedicels of all are
green. The apex of the blade is attenuated, and bears very long
tentacles. Mr. Copland informs me that the leaves of a plant which he
kept for some years were generally covered with captured insects before
they withered.

The leaves do not differ in essential points of structure or of
function from those of the previously described species. Bits of meat
or a little saliva placed on the glands of the exterior tentacles
caused well-marked movement in 3 m., and particles of glass acted in 4
m. The tentacles with the latter particles re-expanded after 22 hrs. A
piece of leaf immersed in a few drops of a solution of one part of
carbonate of ammonia to 437 of water had all the glands blackened and
all the tentacles inflected in 5 m. A bit of raw meat, placed on
several glands in the medial furrow, was well clasped in 2 hrs. 10 m.
by the marginal tentacles on both sides. Bits of roast meat and small
flies did not act quite so quickly; and albumen and fibrin still less
quickly. One of the bits of meat excited so much secretion (which is
always acid) that it flowed some way down the medial furrow, causing
the inflection of the tentacles on both sides as far as it extended.
Particles of glass placed on the glands in the medial furrow did not
stimulate them sufficiently for any motor impulse to be sent to the
outer tentacles. In no case was the blade of the leaf, even the
attenuated apex, at all inflected.

On both the upper and lower surface of the blade there are numerous
minute, almost sessile glands, consisting of four, eight, or twelve
cells. On the lower surface they are pale purple, on the upper
greenish. Nearly similar organs occur on the foot-stalks, but they are
smaller and often in a shrivelled condition. The minute glands on the
blade can absorb rapidly: thus, a piece of leaf was immersed in a
solution of one part of carbonate [page 283] of ammonia to 218 of water
(1 gr. to 2 oz.), and in 5 m. they were all so much darkened as to be
almost black, with their contents aggregated. They do not, as far as I
could observe, secrete spontaneously; but in between 2 and 3 hrs. after
a leaf had been rubbed with a bit of raw meat moistened with saliva,
they seemed to be secreting freely; and this conclusion was afterwards
supported by other appearances. They are, therefore, homologous with
the sessile glands hereafter to be described on the leaves of Dionaea
and Drosophyllum. In this latter genus they are associated, as in the
present case, with glands which secrete spontaneously, that is, without
being excited.

Drosera binata presents another and more remarkable peculiarity,
namely, the presence of a few tentacles on the backs of the leaves,
near their margins. These are perfect in structure; spiral vessels run
up their pedicels; their glands are surrounded by drops of viscid
secretion, and they have the power of absorbing. This latter fact was
shown by the glands immediately becoming black, and the protoplasm
aggregated, when a leaf was placed in a little solution of one part of
carbonate of ammonia to 437 of water. These dorsal tentacles are short,
not being nearly so long as the marginal ones on the upper surface;
some of them are so short as almost to graduate into the minute sessile
glands. Their presence, number, and size, vary on different leaves, and
they are arranged rather irregularly. On the back of one leaf I counted
as many as twenty-one along one side.

These dorsal tentacles differ in one important respect from those on
the upper surface, namely, in not possessing any power of movement, in
whatever manner they may be stimulated. Thus, portions of four leaves
were placed at different times in solutions of carbonate of ammonia
(one part to 437 or 218 of water), and all the tentacles on the upper
surface soon became closely inflected; but the dorsal ones did not
move, though the leaves were left in the solution for many hours, and
though their glands from their blackened colour had obviously absorbed
some of the salt. Rather young leaves should be selected for such
trials, for the dorsal tentacles, as they grow old and begin to wither,
often spontaneously incline towards the middle of the leaf. If these
tentacles had possessed the power of movement, they would not have been
thus rendered more serviceable to the plant; for they are not long
enough to bend round the margin of the leaf so as to reach an insect
caught on the upper surface, Nor would it have been of any use if these
tentacles could have [page 284] moved towards the middle of the lower
surface, for there are no viscid glands there by which insects can be
caught. Although they have no power of movement, they are probably of
some use by absorbing animal matter from any minute insect which may be
caught by them, and by absorbing ammonia from the rain-water. But their
varying presence and size, and their irregular position, indicate that
they are not of much service, and that they are tending towards
abortion. In a future chapter we shall see that Drosophyllum, with its
elongated leaves, probably represents the condition of an early
progenitor of the genus Drosera; and none of the tentacles of
Drosophyllum, neither those on the upper nor lower surface of the
leaves, are capable of movement when excited, though they capture
numerous insects, which serve as nutriment. Therefore it seems that
Drosera binata has retained remnants of certain ancestral
characters—namely a few motionless tentacles on the backs of the
leaves, and fairly well developed sessile glands—which have been lost
by most or all of the other species of the genus.]

Concluding Remarks.—From what we have now seen, there can be little
doubt that most or probably all the species of Drosera are adapted for
catching insects by nearly the same means. Besides the two Australian
species above described, it is said* that two other species from this
country, namely Drosera pallida and Drosera sulphurea, “close their
leaves upon insects with great rapidity: and the same phenomenon is
manifested by an Indian species, D. lunata, and by several of those of
the Cape of Good Hope, especially by D. trinervis.” Another Australian
species, Drosera heterophylla (made by Lindley into a distinct genus,
Sondera) is remarkable from its peculiarly shaped leaves, but I know
nothing of its power of catching insects, for I have seen only dried
specimens. The leaves form minute flattened cups, with the footstalks
attached not to one margin, but to the bottom. The

* ‘Gardener’s Chronicle,’ 1874, p. 209. [page 285]


inner surface and the edges of the cups are studded with tentacles,
which include fibro-vascular bundles, rather different from those seen
by me in any other species; for some of the vessels are barred and
punctured, instead of being spiral. The glands secrete copiously,
judging from the quantity of dried secretion adhering to them. [page
286]




CHAPTER XIII.
DIONAEA MUSCIPULA.


Structure of the leaves—Sensitiveness of the filaments—Rapid movement
of the lobes caused by irritation of the filaments—Glands, their power
of secretion—Slow movement caused by the absorption of animal
matter—Evidence of absorption from the aggregated condition of the
glands—Digestive power of the secretion—Action of chloroform, ether,
and hydrocyanic acid—The manner in which insects are captured—Use of
the marginal spikes—Kinds of insects captured—The transmission of the
motor impulse and mechanism of the movements—Re-expansion of the lobes.


This plant, commonly called Venus’ fly-trap, from the rapidity and
force of its movements, is one of the most wonderful in the world.* It
is a member of the small family of the Droseraceae, and is found only
in the eastern part of North Carolina, growing in damp situations. The
roots are small; those of a moderately fine plant which I examined
consisted of two branches about 1 inch in length, springing from a
bulbous enlargement. They probably serve, as in the case of Drosera,
solely for the absorption of water; for a gardener, who has been very
successful in the cultivation of this plant, grows it, like an
epiphytic orchid, in well-drained damp moss without any soil.** The
form of the bilobed leaf, with its foliaceous footstalk, is shown in
the accompanying drawing (fig. 12).

* Dr. Hooker, in his address to the British Association at Belfast,
1874, has given so full an historical account of the observations which
have been published on the habits of this plant, that it would be
superfluous on my part to repeat them.


** ‘Gardener’s Chronicle,’ 1874, p. 464. [page 287]


The two lobes stand at rather less than a right angle to each other.
Three minute pointed processes or filaments, placed triangularly,
project from the upper surfaces of both; but I have seen two leaves
with four filaments on each side, and another with only two. These
filaments are remarkable from their extreme sensitiveness to a touch,
as shown not by their own movement, but by that of the lobes. The
margins of the leaf are prolonged into sharp rigid projections which I
will call spikes, into each of which a bundle

FIG. 12. (Dionaea muscipula.) Leaf viewed laterally in its expanded
state.

of spiral vessels enters. The spikes stand in such a position that,
when the lobes close, they inter-lock like the teeth of a rat-trap. The
midrib of the leaf, on the lower side, is strongly developed and
prominent.

The upper surface of the leaf is thickly covered, excepting towards the
margins, with minute glands of a reddish or purplish colour, the rest
of the leaf being green. There are no glands on the spikes, or on the
foliaceous footstalk, The glands are formed of from [page 288] twenty
to thirty polygonal cells, filled with purple fluid. Their upper
surface is convex. They stand on very short pedicels, into which spiral
vessels do not enter, in which respect they differ from the tentacles
of Drosera. They secrete, but only when excited by the absorption of
certain matters; and they have the power of absorption. Minute
projections, formed of eight divergent arms of a reddish-brown or
orange colour, and appearing under the microscope like elegant little
flowers, are scattered in considerable numbers over the foot-stalk, the
backs of the leaves, and the spikes, with a few on the upper surface of
the lobes. These octofid projections are no doubt homologous with the
papillae on the leaves of Drosera rotundifolia. There are also a few
very minute, simple, pointed hairs, about 7/12000 (.0148 mm.) of an
inch in length on the backs of the leaves.

The sensitive filaments are formed of several rows of elongated cells,
filled with purplish fluid. They are a little above the 1/20 of an inch
in length; are thin and delicate, and taper to a point. I examined the
bases of several, making sections of them, but no trace of the entrance
of any vessel could be seen. The apex is sometimes bifid or even
trifid, owing to a slight separation between the terminal pointed
cells. Towards the base there is constriction, formed of broader cells,
beneath which there is an articulation, supported on an enlarged base,
consisting of differently shaped polygonal cells. As the filaments
project at right angles to the surface of the leaf, they would have
been liable to be broken whenever the lobes closed together, had it not
been for the articulation which allows them to bend flat down.

These filaments, from their tips to their bases, are exquisitely
sensitive to a momentary touch. It is scarcely [page 289] possible to
touch them ever so lightly or quickly with any hard object without
causing the lobes to close. A piece of very delicate human hair, 2 1/2
inches in length, held dangling over a filament, and swayed to and fro
so as to touch it, did not excite any movement. But when a rather thick
cotton thread of the same length was similarly swayed, the lobes
closed. Pinches of fine wheaten flour, dropped from a height, produced
no effect. The above-mentioned hair was then fixed into a handle, and
cut off so that 1 inch projected; this length being sufficiently rigid
to support itself in a nearly horizontal line. The extremity was then
brought by a slow movement laterally into contact with the tip of a
filament, and the leaf instantly closed. On another occasion two or
three touches of the same kind were necessary before any movement
ensued. When we consider how flexible a fine hair is, we may form some
idea how slight must be the touch given by the extremity of a piece, 1
inch in length, moved slowly.

Although these filaments are so sensitive to a momentary and delicate
touch, they are far less sensitive than the glands of Drosera to
prolonged pressure. Several times I succeeded in placing on the tip of
a filament, by the aid of a needle moved with extreme slowness, bits of
rather thick human hair, and these did not excite movement, although
they were more than ten times as long as those which caused the
tentacles of Drosera to bend; and although in this latter case they
were largely supported by the dense secretion. On the other hand, the
glands of Drosera may be struck with a needle or any hard object, once,
twice, or even thrice, with considerable force, and no movement ensues.
This singular difference in the nature of the sensitiveness of the
filaments of Dionaea and of [page 290] the glands of Drosera evidently
stands in relation to the habits of the two plants. If a minute insect
alights with its delicate feet on the glands of Drosera, it is caught
by the viscid secretion, and the slight, though prolonged pressure,
gives notice of the presence of prey, which is secured by the slow
bending of the tentacles. On the other hand, the sensitive filaments of
Dionaea are not viscid, and the capture of insects can be assured only
by their sensitiveness to a momentary touch, followed by the rapid
closure of the lobes.

As just stated, the filaments are not glandular, and do not secrete.
Nor have they the power of absorption, as may be inferred from drops of
a solution of carbonate of ammonia (one part to 146 of water), placed
on two filaments, not producing any effect on the contents of their
cells, nor causing the lobes to close, When, however, a small portion
of a leaf with an attached filament was cut off and immersed in the
same solution, the fluid within the basal cells became almost instantly
aggregated into purplish or colourless, irregularly shaped masses of
matter. The process of aggregation gradually travelled up the filaments
from cell to cell to their extremities, that is in a reverse course to
what occurs in the tentacles of Drosera when their glands have been
excited. Several other filaments were cut off close to their bases, and
left for 1 hr. 30 m. in a weaker solution of one part of the carbonate
to 218 of water, and this caused aggregation in all the cells,
commencing as before at the bases of the filaments.

Long immersion of the filaments in distilled water likewise causes
aggregation. Nor is it rare to find the contents of a few of the
terminal cells in a spontaneously aggregated condition. The aggregated
[page 291] masses undergo incessant slow changes of form, uniting and
again separating; and some of them apparently revolve round their own
axes. A current of colourless granular protoplasm could also be seen
travelling round the walls of the cells. This current ceases to be
visible as soon as the contents are well aggregated; but it probably
still continues, though no longer visible, owing to all the granules in
the flowing layer having become united with the central masses. In all
these respects the filaments of Dionaea behave exactly like the
tentacles of Drosera.

Notwithstanding this similarity there is one remarkable difference. The
tentacles of Drosera, after their glands have been repeatedly touched,
or a particle of any kind has been placed on them, become inflected and
strongly aggregated. No such effect is produced by touching the
filaments of Dionaea; I compared, after an hour or two, some which had
been touched and some which had not, and others after twenty-five
hours, and there was no difference in the contents of the cells. The
leaves were kept open all the time by clips; so that the filaments were
not pressed against the opposite lobe.

Drops of water, or a thin broken stream, falling from a height on the
filaments, did not cause the blades to close; though these filaments
were afterwards proved to be highly sensitive. No doubt, as in the case
of Drosera, the plant is indifferent to the heaviest shower of rain.
Drops of a solution of a half an ounce of sugar to a fluid ounce of
water were repeatedly allowed to fall from a height on the filaments,
but produced no effect, unless they adhered to them. Again, I blew many
times through a fine pointed tube with my utmost force against the
filaments without any effect; such blowing being received [page 292]
with as much indifference as no doubt is a heavy gale of wind. We thus
see that the sensitiveness of the filaments is of a specialised nature,
being related to a momentary touch rather than to prolonged pressure;
and the touch must not be from fluids, such as air or water, but from
some solid object.

Although drops of water and of a moderately strong solution of sugar,
falling on the filaments, does not excite them, yet the immersion of a
leaf in pure water sometimes caused the lobes to close. One leaf was
left immersed for 1 hr. 10 m., and three other leaves for some minutes,
in water at temperatures varying between 59° and 65° (15° to 18°.3
Cent.) without any effect. One, however, of these four leaves, on being
gently withdrawn from the water, closed rather quickly. The three other
leaves were proved to be in good condition, as they closed when their
filaments were touched. Nevertheless two fresh leaves on being dipped
into water at 75° and 62 1/2° (23°.8 and 16°.9 Cent.) instantly closed.
These were then placed with their footstalks in water, and after 23
hrs. partially re-expanded; on touching their filaments one of them
closed. This latter leaf after an additional 24 hrs. again re-expanded,
and now, on the filaments of both leaves being touched, both closed. We
thus see that a short immersion in water does not at all injure the
leaves, but sometimes excites the lobes to close. The movement in the
above cases was evidently not caused by the temperature of the water.
It has been shown that long immersion causes the purple fluid within
the cells of the sensitive filaments to become aggregated; and the
tentacles of Drosera are acted on in the same manner by long immersion,
often being somewhat inflected. In both cases the result is probably
due to a slight degree of exosmose. [page 293]

I am confirmed in this belief by the effects of immersing a leaf of
Dionaea in a moderately strong solution of sugar; the leaf having been
previously left for 1 hr. 10 m. in water without any effect; for now
the lobes closed rather quickly, the tips of the marginal spikes
crossing in 2 m. 30 s., and the leaf being completely shut in 3 m.
Three leaves were then immersed in a solution of half an ounce of sugar
to a fluid ounce of water, and all three leaves closed quickly. As I
was doubtful whether this was due to the cells on the upper surface of
the lobes, or to the sensitive filaments, being acted on by exosmose,
one leaf was first tried by pouring a little of the same solution in
the furrow between the lobes over the midrib, which is the chief seat
of movement. It was left there for some time, but no movement ensued.
The whole upper surface of leaf was then painted (except close round
the bases of the sensitive filaments, which I could not do without risk
of touching them) with the same solution, but no effect was produced.
So that the cells on the upper surface are not thus affected. But when,
after many trials, I succeeded in getting a drop of the solution to
cling to one of the filaments, the leaf quickly closed. Hence we may, I
think, conclude that the solution causes fluid to pass out of the
delicate cells of the filaments by exosmose; and that this sets up some
molecular change in their contents, analogous to that which must be
produced by a touch.

The immersion of leaves in a solution of sugar affects them for a much
longer time than does an immersion in water, or a touch on the
filaments; for in these latter cases the lobes begin to re-expand in
less than a day. On the other hand, of the three leaves which were
immersed for a short time in the solution, and were then washed by
means of a syringe inserted [page 294] between the lobes, one
re-expanded after two days; a second after seven days; and the third
after nine days. The leaf which closed, owing to a drop of the solution
having adhered to one of the filaments, opened after two days.

I was surprised to find on two occasions that the heat from the rays of
the sun, concentrated by a lens on the bases of several filaments, so
that they were scorched and discoloured, did not cause any movement;
though the leaves were active, as they closed, though rather slowly,
when a filament on the opposite side was touched. On a third trial, a
fresh leaf closed after a time, though very slowly; the rate not being
increased by one of the filaments, which had not been injured, being
touched. After a day these three leaves opened, and were fairly
sensitive when the uninjured filaments were touched. The sudden
immersion of a leaf into boiling water does not cause it to close.
Judging from the analogy of Drosera, the heat in these several cases
was too great and too suddenly applied. The surface of the blade is
very slightly sensitive; It may be freely and roughly handled, without
any movement being caused. A leaf was scratched rather hard with a
needle, but did not close; but when the triangular space between the
three filaments on another leaf was similarly scratched, the lobes
closed. They always closed when the blade or midrib was deeply pricked
or cut. Inorganic bodies, even of large size, such as bits of stone,
glass, &c.—or organic bodies not containing soluble nitrogenous matter,
such as bits of wood, cork, moss,—or bodies containing soluble
nitrogenous matter, if perfectly dry, such as bits of meat, albumen,
gelatine, &c., may be long left (and many were tried) on the lobes, and
no movement is excited. The result, however, is widely different, as we
[page 295] shall presently see, if nitrogenous organic bodies which are
at all damp, are left on the lobes; for these then close by a slow and
gradual movement, very different from that caused by touching one of
the sensitive filaments. The footstalk is not in the least sensitive; a
pin may be driven through it, or it may be cut off, and no movement
follows.

The upper surface of the lobes, as already stated, is thickly covered
with small purplish, almost sessile glands. These have the power both
of secretion and absorption; but unlike those of Drosera, they do not
secrete until excited by the absorption of nitrogenous matter. No other
excitement, as far as I have seen, produces this effect. Objects, such
as bits of wood, cork, moss, paper, stone, or glass, may be left for a
length of time on the surface of a leaf, and it remains quite dry. Nor
does it make any difference if the lobes close over such objects. For
instance, some little balls of blotting paper were placed on a leaf,
and a filament was touched; and when after 24 hrs. the lobes began to
re-open, the balls were removed by the aid of thin pincers, and were
found perfectly dry. On the other hand, if a bit of damp meat or a
crushed fly is placed on the surface of an expanded leaf, the glands
after a time secrete freely. In one such case there was a little
secretion directly beneath the meat in 4 hrs.; and after an additional
3 hrs. there was a considerable quantity both under and close round it.
In another case, after 3 hrs. 40 m., the bit of meat was quite wet. But
none of the glands secreted, excepting those which actually touched the
meat or the secretion containing dissolved animal matter.

If, however, the lobes are made to close over a bit of meat or an
insect, the result is different, for the glands over the whole surface
of the leaf now secrete copiously. [page 296] As in this case the
glands on both sides are pressed against the meat or insect, the
secretion from the first is twice as great as when a bit of meat is
laid on the surface of one lobe; and as the two lobes come into almost
close contact, the secretion, containing dissolved animal matter,
spreads by capillary attraction, causing fresh glands on both sides to
begin secreting in a continually widening circle. The secretion is
almost colourless, slightly mucilaginous, and, judging by the manner in
which it coloured litmus paper, more strongly acid than that of
Drosera. It is so copious that on one occasion, when a leaf was cut
open, on which a small cube of albumen had been placed 45 hrs. before,
drops rolled off the leaf. On another occasion, in which a leaf with an
enclosed bit of roast meat spontaneously opened after eight days, there
was so much secretion in the furrow over the midrib that it trickled
down. A large crushed fly (Tipula) was placed on a leaf from which a
small portion at the base of one lobe had previously been cut away, so
that an opening was left; and through this, the secretion continued to
run down the footstalk during nine days,—that is, for as long a time as
it was observed. By forcing up one of the lobes, I was able to see some
distance between them, and all the glands within sight were secreting
freely.

We have seen that inorganic and non-nitrogenous objects placed on the
leaves do not excite any movement; but nitrogenous bodies, if in the
least degree damp, cause after several hours the lobes to close slowly.
Thus bits of quite dry meat and gelatine were placed at opposite ends
of the same leaf, and in the course of 24 hrs. excited neither
secretion nor movement. They were then dipped in water, their surfaces
dried on blotting paper, and replaced on the same [page 297] leaf, the
plant being now covered with a bell-glass. After 24 hrs. the damp meat
had excited some acid secretion, and the lobes at this end of the leaf
were almost shut. At the other end, where the damp gelatine lay, the
leaf was still quite open, nor had any secretion been excited; so that,
as with Drosera, gelatine is not nearly so exciting a substance as
meat. The secretion beneath the meat was tested by pushing a strip of
litmus paper under it (the filaments not being touched), and this
slight stimulus caused the leaf to shut. On the eleventh day it
reopened; but the end where the gelatine lay, expanded several hours
before the opposite end with the meat.

A second bit of roast meat, which appeared dry, though it had not been
purposely dried, was left for 24 hrs. on a leaf, caused neither
movement nor secretion. The plant in its pot was now covered with a
bell-glass, and the meat absorbed some moisture from the air; this
sufficed to excite acid secretion, and by the next morning the leaf was
closely shut. A third bit of meat, dried so as to be quite brittle, was
placed on a leaf under a bell-glass, and this also became in 24 hrs.
slightly damp, and excited some acid secretion, but no movement.

A rather large piece of perfectly dry albumen was left at one end of a
leaf for 24 hrs. without any effect. It was then soaked for a few
minutes in water, rolled about on blotting paper, and replaced on the
leaf; in 9 hrs. some slightly acid secretion was excited, and in 24
hrs. this end of the leaf was partially closed. The bit of albumen,
which was now surrounded by much secretion, was gently removed, and
although no filament was touched, the lobes closed. In this and the
previous case, it appears that the absorption of animal matter by the
glands renders [page 298] the surface of the leaf much more sensitive
to a touch than it is in its ordinary state; and this is a curious
fact. Two days afterwards the end of the leaf where nothing had been
placed began to open, and on the third day was much more open than the
opposite end where the albumen had lain.

Lastly, large drops of a solution of one part of carbonate of ammonia
to 146 of water were placed on some leaves, but no immediate movement
ensued. I did not then know of the slow movement caused by animal
matter, otherwise I should have observed the leaves for a longer time,
and they would probably have been found closed, though the solution
(judging from Drosera) was, perhaps, too strong.

From the foregoing cases it is certain that bits of meat and albumen,
if at all damp, excite not only the glands to secrete, but the lobes to
close. This movement is widely different from the rapid closure caused
by one of the filaments being touched. We shall see its importance when
we treat of the manner in which insects are captured. There is a great
contrast between Drosera and Dionaea in the effects produced by
mechanical irritation on the one hand, and the absorption of animal
matter on the other. Particles of glass placed on the glands of the
exterior tentacles of Drosera excite movement within nearly the same
time, as do particles of meat, the latter being rather the most
efficient; but when the glands of the disc have bits of meat given
them, they transmit a motor impulse to the exterior tentacles much more
quickly than do these glands when bearing inorganic particles, or when
irritated by repeated touches. On the other hand, with Dionaea,
touching the filaments excites incomparably quicker movement than the
absorption of animal matter by the glands. Nevertheless, in [page 299]
certain cases, this latter stimulus is the more powerful of the two. On
three occasions leaves were found which from some cause were torpid, so
that their lobes closed only slightly, however much their filaments
were irritated; but on inserting crushed insects between the lobes,
they became in a day closely shut.

The facts just given plainly show that the glands have the power of
absorption, for otherwise it is impossible that the leaves should be so
differently affected by non-nitrogenous and nitrogenous bodies, and
between these latter in a dry and damp condition. It is surprising how
slightly damp a bit of meat or albumen need be in order to excite
secretion and afterwards slow movement, and equally surprising how
minute a quantity of animal matter, when absorbed, suffices to produce
these two effects. It seems hardly credible, and yet it is certainly a
fact, that a bit of hard-boiled white of egg, first thoroughly dried,
then soaked for some minutes in water and rolled on blotting paper,
should yield in a few hours enough animal matter to the glands to cause
them to secrete, and afterwards the lobes to close. That the glands
have the power of absorption is likewise shown by the very different
lengths of time (as we shall presently see) during which the lobes
remain closed over insects and other bodies yielding soluble
nitrogenous matter, and over such as do not yield any. But there is
direct evidence of absorption in the condition of the glands which have
remained for some time in contact with animal matter. Thus bits of meat
and crushed insects were several times placed on glands, and these were
compared after some hours with other glands from distant parts of the
same leaf. The latter showed not a trace of aggregation, whereas those
which had been in contact with the animal matter were [page 300] well
aggregated. Aggregation may be seen to occur very quickly if a piece of
a leaf is immersed in a weak solution of carbonate of ammonia. Again,
small cubes of albumen and gelatine were left for eight days on a leaf,
which was then cut open. The whole surface was bathed with acid
secretion, and every cell in the many glands which were examined had
its contents aggregated in a beautiful manner into dark or pale purple,
or colourless globular masses of protoplasm. These underwent incessant
slow changes of forms; sometimes separating from one another and then
reuniting, exactly as in the cells of Drosera. Boiling water makes the
contents of the gland-cells white and opaque, but not so purely white
and porcelain-like as in the case of Drosera. How living insects, when
naturally caught, excite the glands to secrete so quickly as they do, I
know not; but I suppose that the great pressure to which they are
subjected forces a little excretion from either extremity of their
bodies, and we have seen that an extremely small amount of nitrogenous
matter is sufficient to excite the glands.

Before passing on to the subject of digestion, I may state that I
endeavoured to discover, with no success, the functions of the minute
octofid processes with which the leaves are studded. From facts
hereafter to be given in the chapters on Aldrovanda and Utricularia, it
seemed probable that they served to absorb decayed matter left by the
captured insects; but their position on the backs of the leaves and on
the footstalks rendered this almost impossible. Nevertheless, leaves
were immersed in a solution of one part of urea to 437 of water, and
after 24 hrs. the orange layer of protoplasm within the arms of these
processes did not appear more aggregated than in other speci- [page
301] mens kept in water, I then tried suspending a leaf in a bottle
over an excessively putrid infusion of raw meat, to see whether they
absorbed the vapour, but their contents were not affected.

Digestive Power of the Secretion.*—When a leaf closes over any object,
it may be said to form itself into a temporary stomach; and if the
object yields ever so little animal matter, this serves, to use
Schiff’s expression, as a peptogene, and the glands on the surface pour
forth their acid secretion, which acts like the gastric juice of
animals. As so many experiments were tried on the digestive power of
Drosera, only a few were made with Dionaea, but they were amply
sufficient to prove that it digests, This plant, moreover, is not so
well fitted as Drosera for observation, as the process goes on within
the closed lobes. Insects, even beetles, after being subjected to the
secretion for several days, are surprisingly softened, though their
chitinous coats are not corroded,

[Experiment 1.—A cube of albumen of 1/10 of an inch (2.540 mm.) was
placed at one end of a leaf, and at the other end an oblong piece of
gelatine, 1/5 of an inch (5.08 mm.) long, and

* Dr. W.M. Canby, of Wilmington, to whom I am much indebted for
information regarding Dionaea in its native home, has published in the
‘Gardener’s Monthly,’ Philadelphia, August 1868, some interesting
observations. He ascertained that the secretion digests animal matter,
such as the contents of insects, bits of meat, &c. and that the
secretion is reabsorbed. He was also well aware that the lobes remain
closed for a much longer time when in contact with animal matter than
when made to shut by a mere touch, or over objects not yielding soluble
nutriment; and that in these latter cases the glands do not secrete.
The Rev. Dr. Curtis first observed (‘Boston Journal Nat. Hist.’ vol.
i., p. 123) the secretion from the glands. I may here add that a
gardener, Mr. Knight, is said (Kirby and Spencer’s ‘Introduction to
Entomology,’ 1818, vol. i., p. 295) to have found that a plant of the
Dionaea, on the leaves of which “he laid fine filaments of raw beef,
was much more luxuriant in its growth than others not so treated.”
[page 302]


1/10 broad; the leaf was then made to close. It was cut open after 45
hrs. The albumen was hard and compressed, with its angles only a little
rounded; the gelatine was corroded into an oval form; and both were
bathed in so much acid secretion that it dropped off the leaf. The
digestive process apparently is rather slower than in Drosera, and this
agrees with the length of time during which the leaves remain closed
over digestible objects.

Experiment 2.—A bit of albumen 1/10 of an inch square, but only 1/20 in
thickness, and a piece of gelatine of the same size as before, were
placed on a leaf, which eight days afterwards was cut open. The surface
was bathed with slightly adhesive, very acid secretion, and the glands
were all in an aggregated condition. Not a vestige of the albumen or
gelatine was left. Similarly sized pieces were placed at the same time
on wet moss on the same pot, so that they were subjected to nearly
similar conditions; after eight days these were brown, decayed, and
matted with fibres of mould, but had not disappeared.

Experiment 3.—A piece of albumen 3/20 of an inch (3.81 mm.) long, and
1/20 broad and thick, and a piece of gelatine of the same size as
before, were placed on another leaf, which was cut open after seven
days; not a vestige of either substance was left, and only a moderate
amount of secretion on the surface.

Experiment 4.—Pieces of albumen and gelatine, of the same size as in
the last experiment, were placed on a leaf, which spontaneously opened
after twelve days, and here again not a vestige of either was left, and
only a little secretion at one end of the midrib.

Experiment 5.—Pieces of albumen and gelatine of the same size were
placed on another leaf, which after twelve days was still firmly
closed, but had begun to wither; it was cut open, and contained nothing
except a vestige of brown matter where the albumen had lain.

Experiment 6.—A cube of albumen of 1/10 of an inch and a piece of
gelatine of the same size as before were placed on a leaf, which opened
spontaneously after thirteen days, The albumen, which was twice as
thick as in the latter experiments, was too large; for the glands in
contact with it were injured and were dropping off; a film also of
albumen of a brown colour, matted with mould, was left. All the
gelatine was absorbed, and there was only a little acid secretion left
on the midrib.

Experiment 7.—A bit of half roasted meat (not measured) and a bit of
gelatine were placed on the two ends of a leaf, which [page 303] opened
spontaneously after eleven days; a vestige of the meat was left, and
the surface of the leaf was here blackened; the gelatine had all
disappeared.

Experiment 8.—A bit of half roasted meat (not measured) was placed on a
leaf which was forcibly kept open by a clip, so that it was moistened
with the secretion (very acid) only on its lower surface. Nevertheless,
after only 22 1/2 hrs. it was surprisingly softened, when compared with
another bit of the same meat which had been kept damp.

Experiment 9.—A cube of 1/10 of an inch of very compact roasted beef
was placed on a leaf, which opened spontaneously after twelve days; so
much feebly acid secretion was left on the leaf that it trickled off.
The meat was completely disintegrated, but not all dissolved; there was
no mould. The little mass was placed under the microscope; some of the
fibrillae in the middle still exhibited transverse striae; others
showed not a vestige of striae; and every gradation could be traced
between these two states. Globules, apparently of fat, and some
undigested fibro-elastic tissue remained. The meat was thus in the same
state as that formerly described, which was half digested by Drosera.
Here, again, as in the case of albumen, the digestive process seems
slower than in Drosera. At the opposite end of the same leaf, a firmly
compressed pellet of bread had been placed; this was completely
disintegrated, I suppose, owing to the digestion of the gluten, but
seemed very little reduced in bulk.

Experiment 10.—A cube of 1/20 of an inch of cheese and another of
albumen were placed at opposite ends of the same leaf. After nine days
the lobes opened spontaneously a little at the end enclosing the
cheese, but hardly any or none was dissolved, though it was softened
and surrounded by secretion. Two days subsequently the end with the
albumen also opened spontaneously (i.e. eleven days after it was put
on), a mere trace in a blackened and dry condition being left.

Experiment 11.—The same experiment with cheese and albumen repeated on
another and rather torpid leaf. The lobes at the end with the cheese,
after an interval of six days, opened spontaneously a little; the cube
of cheese was much softened, but not dissolved, and but little, if at
all, reduced in size. Twelve hours afterwards the end with the albumen
opened, which now consisted of a large drop of transparent, not acid,
viscid fluid.

Experiment 12.—Same experiment as the two last, and here again the leaf
at the end enclosing the cheese opened before the [page 304] opposite
end with the albumen; but no further observations were made.

Experiment 13.—A globule of chemically prepared casein, about 1/10 of
an inch in diameter, was placed on a leaf, which spontaneously opened
after eight days. The casein now consisted of a soft sticky mass, very
little, if at all, reduced in size, but bathed in acid secretion.]

These experiments are sufficient to show that the secretion from the
glands of Dionaea dissolves albumen, gelatine, and meat, if too large
pieces are not given. Globules of fat and fibro-elastic tissue are not
digested. The secretion, with its dissolved matter, if not in excess,
is subsequently absorbed. On the other hand, although chemically
prepared casein and cheese (as in the case of Drosera) excite much acid
secretion, owing, I presume, to the absorption of some included
albuminous matter, these substances are not digested, and are not
appreciably, if at all, reduced in bulk.

[Effects of the Vapours of Chloroform, Sulphuric Ether, and Hydrocyanic
Acid.—A plant bearing one leaf was introduced into a large bottle with
a drachm (3.549 ml.) of chloroform, the mouth being imperfectly closed
with cotton-wool. The vapour caused in 1 m. the lobes to begin moving
at an imperceptibly slow rate; but in 3 m. the spikes crossed, and the
leaf was soon completely shut. The dose, however, was much too large,
for in between 2 and 3 hrs. the leaf appeared as if burnt, and soon
died.

Two leaves were exposed for 30 m. in a 2-oz: vessel to the vapour of 30
minims (1.774 ml.) of sulphuric ether. One leaf closed after a time, as
did the other whilst being removed from the vessel without being
touched. Both leaves were greatly injured. Another leaf, exposed for 20
m. to 15 minims of ether, closed its lobes to a certain extent, and the
sensitive filaments were now quite insensible. After 24 hrs. this leaf
recovered its sensibility, but was still rather torpid. A leaf exposed
in a large bottle for only 3 m. to ten drops was rendered insensible.
After 52 m. it recovered its sensibility, and when one of the filaments
was touched, the lobes closed. It began [page 305] to reopen after 20
hrs. Lastly another leaf was exposed for 4 m. to only four drops of the
ether; it was rendered insensible, and did not close when its filaments
were repeatedly touched, but closed when the end of the open leaf was
cut off. This shows either that the internal parts had not been
rendered insensible, or that an incision is a more powerful stimulus
than repeated touches on the filaments. Whether the larger doses of
chloroform and ether, which caused the leaves to close slowly, acted on
the sensitive filaments or on the leaf itself, I do not know.

Cyanide of potassium, when left in a bottle, generates prussic or
hydrocyanic acid. A leaf was exposed for 1 hr. 35 m. to the vapour thus
formed; and the glands became within this time so colourless and
shrunken as to be scarcely visible, and I at first thought that they
had all dropped off. The leaf was not rendered insensible; for as soon
as one of the filaments was touched it closed. It had, however,
suffered, for it did not reopen until nearly two days had passed, and
was not even then in the least sensitive. After an additional day it
recovered its powers, and closed on being touched and subsequently
reopened. Another leaf behaved in nearly the same manner after a
shorter exposure to this vapour.]

On the Manner in which Insects are caught.—We will now consider the
action of the leaves when insects happen to touch one of the sensitive
filaments. This often occurred in my greenhouse, but I do not know
whether insects are attracted in any special way by the leaves. They
are caught in large numbers by the plant in its native country. As soon
as a filament is touched, both lobes close with astonishing quickness;
and as they stand at less than a right angle to each other, they have a
good chance of catching any intruder. The angle between the blade and
footstalk does not change when the lobes close. The chief seat of
movement is near the midrib, but is not confined to this part; for, as
the lobes come together, each curves inwards across its whole breadth;
the marginal spikes however, not becoming curved. This move- [page 306]
ment of the whole lobe was well seen in a leaf to which a large fly had
been given, and from which a large portion had been cut off the end of
one lobe; so that the opposite lobe, meeting with no resistance in this
part, went on curving inwards much beyond the medial line. The whole of
the lobe, from which a portion had been cut, was afterwards removed,
and the opposite lobe now curled completely over, passing through an
angle of from 120o to 130o, so as to occupy a position almost at right
angles to that which it would have held had the opposite lobe been
present.

From the curving inwards of the two lobes, as they move towards each
other, the straight marginal spikes intercross by their tips at first,
and ultimately by their bases. The leaf is then completely shut and
encloses a shallow cavity. If it has been made to shut merely by one of
the sensitive filaments having been touched, or if it includes an
object not yielding soluble nitrogenous matter, the two lobes retain
their inwardly concave form until they re-expand. The re-expansion
under these circumstances—that is when no organic matter is
enclosed—was observed in ten cases. In all of these, the leaves
re-expanded to about two-thirds of the full extent in 24 hrs. from the
time of closure. Even the leaf from which a portion of one lobe had
been cut off opened to a slight degree within this same time. In one
case a leaf re-expanded to about two-thirds of the full extent in 7
hrs., and completely in 32 hrs.; but one of its filaments had been
touched merely with a hair just enough to cause the leaf to close. Of
these ten leaves only a few re-expanded completely in less than two
days, and two or three required even a little longer time. Before,
however, they fully re-expand, they are ready to close [page 307]
instantly if their sensitive filaments are touched. How many times a
leaf is capable of shutting and opening if no animal matter is left
enclosed, I do not know; but one leaf was made to close four times,
reopening afterwards, within six days, On the last occasion it caught a
fly, and then remained closed for many days.

This power of reopening quickly after the filaments have been
accidentally touched by blades of grass, or by objects blown on the
leaf by the wind, as occasionally happens in its native place,* must be
of some importance to the plant; for as long as a leaf remains closed,
it cannot of course capture an insect.

When the filaments are irritated and a leaf is made to shut over an
insect, a bit of meat, albumen, gelatine, casein, and, no doubt, any
other substance containing soluble nitrogenous matter, the lobes,
instead of remaining concave, thus including a concavity, slowly press
closely together throughout their whole breadth. As this takes place,
the margins gradually become a little everted, so that the spikes,
which at first intercrossed, at last project in two parallel rows. The
lobes press against each other with such force that I have seen a cube
of albumen much flattened, with distinct impressions of the little
prominent glands; but this latter circumstance may have been partly
caused by the corroding action of the secretion. So firmly do they
become pressed together that, if any large insect or other object has
been caught, a corresponding projection on the outside of the leaf is
distinctly visible. When the two lobes are thus completely shut, they

* According to Dr. Curtis, in ‘Boston Journal of Nat. Hist,’ vol. i
1837, p. 123. [page 308]


resist being opened, as by a thin wedge driven between them, with
astonishing force, and are generally ruptured rather than yield. If not
ruptured, they close again, as Dr. Canby informs me in a letter, “with
quite a loud flap.” But if the end of a leaf is held firmly between the
thumb and finger, or by a clip, so that the lobes cannot begin to
close, they exert, whilst in this position, very little force.

I thought at first that the gradual pressing together of the lobes was
caused exclusively by captured insects crawling over and repeatedly
irritating the sensitive filaments; and this view seemed the more
probable when I learnt from Dr. Burdon Sanderson that whenever the
filaments of a closed leaf are irritated, the normal electric current
is disturbed. Nevertheless, such irritation is by no means necessary,
for a dead insect, or a bit of meat, or of albumen, all act equally
well; proving that in these cases it is the absorption of animal matter
which excites the lobes slowly to press close together. We have seen
that the absorption of an extremely small quantity of such matter also
causes a fully expanded leaf to close slowly; and this movement is
clearly analogous to the slow pressing together of the concave lobes.
This latter action is of high functional importance to the plant, for
the glands on both sides are thus brought into contact with a captured
insect, and consequently secrete. The secretion with animal matter in
solution is then drawn by capillary attraction over the whole surface
of the leaf, causing all the glands to secrete and allowing them to
absorb the diffused animal matter. The movement, excited by the
absorption of such matter, though slow, suffices for its final purpose,
whilst the movement excited by one of the sensitive filaments being
touched is rapid, and this is indis- [page 309] pensable for the
capturing of insects. These two movements, excited by two such widely
different means, are thus both well adapted, like all the other
functions of the plant, for the purposes which they subserve.

There is another wide difference in the action of leaves which enclose
objects, such as bits of wood, cork, balls of paper, or which have had
their filaments merely touched, and those which enclose organic bodies
yielding soluble nitrogenous matter. In the former case the leaves, as
we have seen, open in under 24 hrs. and are then ready, even before
being fully-expanded, to shut again. But if they have closed over
nitrogen-yielding bodies, they remain closely shut for many days; and
after re-expanding are torpid, and never act again, or only after a
considerable interval of time. In four instances, leaves after catching
insects never reopened, but began to wither, remaining closed—in one
case for fifteen days over a fly; in a second, for twenty-four days,
though the fly was small; in a third for twenty-four days over a
woodlouse; and in a fourth, for thirty-five days over a large Tipula.
In two other cases leaves remained closed for at least nine days over
flies, and for how many more I do not know. It should, however, be
added that in two instances in which very small insects had been
naturally caught the leaf opened as quickly as if nothing had been
caught; and I suppose that this was due to such small insects not
having been crushed or not having excreted any animal matter, so that
the glands were not excited. Small angular bits of albumen and gelatine
were placed at both ends of three leaves, two of which remained closed
for thirteen and the other for twelve days. Two other leaves remained
closed over bits of [page 310] meat for eleven days, a third leaf for
eight days, and a fourth (but this had been cracked and injured) for
only six days. Bits of cheese, or casein, were placed at one end and
albumen at the other end of three leaves; and the ends with the former
opened after six, eight, and nine days, whilst the opposite ends opened
a little later. None of the above bits of meat, albumen, &c., exceeded
a cube of 1/10 of an inch (2.54 mm.) in size, and were sometimes
smaller; yet these small portions sufficed to keep the leaves closed
for many days. Dr. Canby informs me that leaves remain shut for a
longer time over insects than over meat; and from what I have seen, I
can well believe that this is the case, especially if the insects are
large.

In all the above cases, and in many others in which leaves remained
closed for a long but unknown period over insects naturally caught,
they were more or less torpid when they reopened. Generally they were
so torpid during many succeeding days that no excitement of the
filaments caused the least movement. In one instance, however, on the
day after a leaf opened which had clasped a fly, it closed with extreme
slowness when one of its filaments was touched; and although no object
was left enclosed, it was so torpid that it did not re-open for the
second time until 44 hrs. had elapsed. In a second case, a leaf which
had expanded after remaining closed for at least nine days over a fly,
when greatly irritated, moved one alone of its two lobes, and retained
this unusual position for the next two days. A third case offers the
strongest exception which I have observed; a leaf, after remaining
clasped for an unknown time over a fly, opened, and when one of its
filaments was touched, closed, though rather slowly. Dr. Canby, [page
311] who observed in the United States a large number of plants which,
although not in their native site, were probably more vigorous than my
plants, informs me that he has “several times known vigorous leaves to
devour their prey several times; but ordinarily twice, or, quite often,
once was enough to render them unserviceable.” Mrs. Treat, who
cultivated many plants in New Jersey, also informs me that “several
leaves caught successively three insects each, but most of them were
not able to digest the third fly, but died in the attempt. Five leaves,
however, digested each three flies, and closed over the fourth, but
died soon after the fourth capture. Many leaves did not digest even one
large insect.” It thus appears that the power of digestion is somewhat
limited, and it is certain that leaves always remain clasped for many
days over an insect, and do not recover their power of closing again
for many subsequent days. In this respect Dionaea differs from Drosera,
which catches and digests many insects after shorter intervals of time.

We are now prepared to understand the use of the marginal spikes, which
form so conspicuous a feature in the appearance of the plant (fig. 12,
p. 287), and which at first seemed to me in my ignorance useless
appendages. From the inward curvature of the lobes as they approach
each other, the tips of the marginal spikes first intercross, and
ultimately their bases. Until the edges of the lobes come into contact,
elongated spaces between the spikes, varying from the 1/15 to the 1/10
of an inch (1.693 to 2.54 mm.) in breadth, according to the size of the
leaf, are left open. Thus an insect, if its body is not thicker than
these measurements, can easily escape between the crossed spikes, when
disturbed by the closing lobes and in- [page 312] creasing darkness;
and one of my sons actually saw a small insect thus escaping. A
moderately large insect, on the other hand, if it tries to escape
between the bars will surely be pushed back again into its horrid
prison with closing walls, for the spikes continue to cross more and
more until the edges of the lobes come into contact. A very strong
insect, however, would be able to free itself, and Mrs. Treat saw this
effected by a rose-chafer (Macrodactylus subspinosus) in the United
States. Now it would manifestly be a great disadvantage to the plant to
waste many days in remaining clasped over a minute insect, and several
additional days or weeks in afterwards recovering its sensibility;
inasmuch as a minute insect would afford but little nutriment. It would
be far better for the plant to wait for a time until a moderately large
insect was captured, and to allow all the little ones to escape; and
this advantage is secured by the slowly intercrossing marginal spikes,
which act like the large meshes of a fishing-net, allowing the small
and useless fry to escape.

As I was anxious to know whether this view was correct—and as it seems
a good illustration of how cautious we ought to be in assuming, as I
had done with respect to the marginal spikes, that any fully developed
structure is useless—I applied to Dr. Canby. He visited the native site
of the plant, early in the season, before the leaves had grown to their
full size, and sent me fourteen leaves, containing naturally captured
insects. Four of these had caught rather small insects, viz. three of
them ants, and the fourth a rather small fly, but the other ten had all
caught large insects, namely, five elaters, two chrysomelas, a
curculio, a thick and broad spider, and a scolopendra. Out of these ten
insects, no less than eight [page 313] were beetles,* and out of the
whole fourteen there was only one, viz. a dipterous insect, which could
readily take flight. Drosera, on the other hand, lives chiefly on
insects which are good flyers, especially Diptera, caught by the aid of
its viscid secretion. But what most concerns us is the size of the ten
larger insects. Their average length from head to tail was .256 of an
inch, the lobes of the leaves being on an average .53 of an inch in
length, so that the insects were very nearly half as long as the leaves
within which they were enclosed. Only a few of these leaves, therefore,
had wasted their powers by capturing small prey, though it is probable
that many small insects had crawled over them and been caught, but had
then escaped through the bars.

The Transmission of the Motor Impulse, and Means of Movement.—It is
sufficient to touch any one of the six filaments to cause both lobes to
close, these becoming at the same time incurved throughout their whole
breadth. The stimulus must therefore radiate in all directions from any
one filament. It must also be transmitted with much rapidity across the
leaf, for in all ordinary cases both lobes close simultaneously, as far
as the eye can judge. Most physiologists believe that in irritable
plants the excitement is transmitted along, or in close connection
with, the fibro-vascular bundles. In Dionaea, the course of these
vessels (composed of spiral and ordinary vascular

* Dr. Canby remarks (‘Gardener’s Monthly,’ August 1868), “as a general
thing beetles and insects of that kind, though always killed, seem to
be too hard-shelled to serve as food, and after a short time are
rejected.” I am surprised at this statement, at least with respect to
such beetles as elaters, for the five which I examined were in an
extremely fragile and empty condition, as if all their internal parts
had been partially digested. Mrs. Treat informs me that the plants
which she cultivated in New Jersey chiefly caught Diptera. [page 314]


tissue) seems at first sight to favour this belief; for they run up the
midrib in a great bundle, sending off small bundles almost at right
angles on each side. These bifurcate occasionally as they extend
towards the margin, and close to the margin small branches from
adjoining vessels unite and enter the marginal spikes. At some of these
points of union the vessels form curious loops, like those described
under Drosera. A continuous zigzag line of vessels thus runs round the
whole circumference of the leaf, and in the midrib all the vessels are
in close contact; so that all parts of the leaf seem to be brought into
some degree of communication. Nevertheless, the presence of vessels is
not necessary for the transmission of the motor impulse, for it is
transmitted from the tips of the sensitive filaments (these being about
the 1/20 of an inch in length), into which no vessels enter; and these
could not have been overlooked, as I made thin vertical sections of the
leaf at the bases of the filaments.

On several occasions, slits about the 1/10 of an inch in length were
made with a lancet, close to the bases of the filaments, parallel to
the midrib, and, therefore, directly across the course of the vessels.
These were made sometimes on the inner and sometimes on the outer sides
of the filaments; and after several days, when the leaves had reopened,
these filaments were touched roughly (for they were always rendered in
some degree torpid by the operation), and the lobes then closed in the
ordinary manner, though slowly, and sometimes not until after a
considerable interval of time. These cases show that the motor impulse
is not transmitted along the vessels, and they further show that there
is no necessity for a direct line of communication from the filament
which is [page 315] touched towards the midrib and opposite lobe, or
towards the outer parts of the same lobe.

Two slits near each other, both parallel to the midrib, were next made
in the same manner as before, one on each side of the base of a
filament, on five distinct leaves, so that a little slip bearing a
filament was connected with the rest of the leaf only at its two ends.
These slips were nearly of the same size; one was carefully measured;
it was .12 of an inch (3.048 mm.) in length, and .08 of an inch (2.032
mm.) in breadth; and in the middle stood the filament. Only one of
these slips withered and perished. After the leaf had recovered from
the operation, though the slits were still open, the filaments thus
circumstanced were roughly touched, and both lobes, or one alone,
slowly closed. In two instances touching the filament produced no
effect; but when the point of a needle was driven into the slip at the
base of the filament, the lobes slowly closed. Now in these cases the
impulse must have proceeded along the slip in a line parallel to the
midrib, and then have radiated forth, either from both ends or from one
end alone of the slip, over the whole surface of the two lobes.

Again, two parallel slits, like the former ones, were made, one on each
side of the base of a filament, at right angles to the midrib. After
the leaves (two in number) had recovered, the filaments were roughly
touched, and the lobes slowly closed; and here the impulse must have
travelled for a short distance in a line at right angles to the midrib,
and then have radiated forth on all sides over both lobes. These
several cases prove that the motor impulse travels in all directions
through the cellular tissue, independently of the course of the
vessels.

With Drosera we have seen that the motor impulse [page 316] is
transmitted in like manner in all directions through the cellular
tissue; but that its rate is largely governed by the length of the
cells and the direction of their longer axes. Thin sections of a leaf
of Dionaea were made by my son, and the cells, both those of the
central and of the more superficial layers, were found much elongated,
with their longer axes directed towards the midrib; and it is in this
direction that the motor impulse must be sent with great rapidity from
one lobe to the other, as both close simultaneously. The central
parenchymatous cells are larger, more loosely attached together, and
have more delicate walls than the more superficial cells. A thick mass
of cellular tissue forms the upper surface of the midrib over the great
central bundle of vessels.

When the filaments were roughly touched, at the bases of which slits
had been made, either on both sides or on one side, parallel to the
midrib or at right angles to it, the two lobes, or only one, moved. In
one of these cases, the lobe on the side which bore the filament that
was touched moved, but in three other cases the opposite lobe alone
moved; so that an injury which was sufficient to prevent a lobe moving
did not prevent the transmission from it of a stimulus which excited
the opposite lobe to move. We thus also learn that, although normally
both lobes move together, each has the power of independent movement. A
case, indeed, has already been given of a torpid leaf that had lately
re-opened after catching an insect, of which one lobe alone moved when
irritated. Moreover, one end of the same lobe can close and re- expand,
independently of the other end, as was seen in some of the foregoing
experiments.

When the lobes, which are rather thick, close, no trace of wrinkling
can be seen on any part of their upper [page 317] surfaces, It appears
therefore that the cells must contract. The chief seat of the movement
is evidently in the thick mass of cells which overlies the central
bundle of vessels in the midrib. To ascertain whether this part
contracts, a leaf was fastened on the stage of the microscope in such a
manner that the two lobes could not become quite shut, and having made
two minute black dots on the midrib, in a transverse line and a little
towards one side, they were found by the micrometer to be 17/1000 of an
inch apart. One of the filaments was then touched and the lobes closed;
but as they were prevented from meeting, I could still see the two
dots, which now were 15/1000 of an inch apart, so that a small portion
of the upper surface of the midrib had contracted in a transverse line
2/1000 of an inch (.0508 mm.).

We know that the lobes, whilst closing, become slightly incurved
throughout their whole breadth. This movement appears to be due to the
contraction of the superficial layers of cells over the whole upper
surface. In order to observe their contraction, a narrow strip was cut
out of one lobe at right angles to the midrib, so that the surface of
the opposite lobe could be seen in this part when the leaf was shut.
After the leaf had recovered from the operation and had re-expanded,
three minute black dots were made on the surface opposite to the slit
or window, in a line at right angles to the midrib. The distance
between the dots was found to be 40/1000 of an inch, so that the two
extreme dots were 80/1000 of an inch apart. One of the filaments was
now touched and the leaf closed. On again measuring the distances
between the dots, the two next to the midrib were nearer together by 1
to 2/1000 of an inch, and the two further dots by 3 to 4/1000 of an
inch, than they were before; so that the two extreme [page 318] dots
now stood about 5/1000 of an inch (.127 mm.) nearer together than
before. If we suppose the whole upper surface of the lobe, which was
400/1000 of an inch in breadth, to have contracted in the same
proportion, the total contraction will have amounted to about 25/1000
or 1/40 of an inch (.635 mm.); but whether this is sufficient to
account for the slight inward curvature of the whole lobe, I am unable
to say.

Finally, with respect to the movement of the leaves, the wonderful
discovery made by Dr. Burdon Sanderson* is now universally known;
namely that there exists a normal electrical current in the blade and
footstalk; and that when the leaves are irritated, the current is
disturbed in the same manner as takes place during the contraction of
the muscle of an animal.

The Re-expansion of the Leaves.—This is effected at an insensibly slow
rate, whether or not any object is enclosed.** One lobe can re-expand
by itself, as occurred with the torpid leaf of which one lobe alone had
closed. We have also seen in the experiments with cheese and albumen
that the two ends of the same lobe can re-expand to a certain extent
independently of each other. But in all ordinary cases both lobes open
at the same time. The re-expansion is not determined by the sensitive
filaments; all three filaments on one lobe were cut off close to their
bases; and the three

* Proc. Royal Soc.’ vol. xxi. p. 495; and lecture at the Royal
Institution, June 5, 1874, given in ‘Nature,’ 1874, pp. 105 and 127.


** Nuttall, in his ‘Gen. American Plants,’ p. 277 (note), says that,
whilst collecting this plant in its native home, “I had occasion to
observe that a detached leaf would make repeated efforts towards
disclosing itself to the influence of the sun; these attempts consisted
in an undulatory motion of the marginal ciliae, accompanied by a
partial opening and succeeding collapse of the lamina, which at length
terminated in a complete expansion and in the destruction of
sensibility.” I am indebted to Prof. Oliver for this reference; but I
do not understand what took place. [page 319]


leaves thus treated re-expanded,—one to a partial extent in 24 hrs.,—a
second to the same extent in 48 hrs., and the third, which had been
previously injured, not until the sixth day. These leaves after their
re-expansion closed quickly when the filaments on the other lobe were
irritated. These were then cut off one of the leaves, so that none were
left. This mutilated leaf, notwithstanding the loss of all its
filaments, re-expanded in two days in the usual manner. When the
filaments have been excited by immersion in a solution of sugar, the
lobes do not expand so soon as when the filaments have been merely
touched; and this, I presume, is due to their having been strongly
affected through exosmose, so that they continue for some time to
transmit a motor impulse to the upper surface of the leaf.

The following facts make me believe that the several layers of cells
forming the lower surface of the leaf are always in a state of tension;
and that it is owing to this mechanical state, aided probably by fresh
fluid being attracted into the cells, that the lobes begin to separate
or expand as soon as the contraction of the upper surface diminishes. A
leaf was cut off and suddenly plunged perpendicularly into boiling
water: I expected that the lobes would have closed, but instead of
doing so, they diverged a little. I then took another fine leaf, with
the lobes standing at an angle of nearly 80o to each other; and on
immersing it as before, the angle suddenly increased to 90o. A third
leaf was torpid from having recently re-expanded after having caught a
fly, so that repeated touches of the filaments caused not the least
movement; nevertheless, when similarly immersed, the lobes separated a
little. As these leaves were inserted perpendicularly into the boiling
water, both surfaces and the filaments [page 320] must have been
equally affected; and I can understand the divergence of the lobes only
by supposing that the cells on the lower side, owing to their state of
tension, acted mechanically and thus suddenly drew the lobes a little
apart, as soon as the cells on the upper surface were killed and lost
their contractile power. We have seen that boiling water in like manner
causes the tentacles of Drosera to curve backwards; and this is an
analogous movement to the divergence of the lobes of Dionaea.

In some concluding remarks in the fifteenth chapter on the Droseraceae,
the different kinds of irritability possessed by the several genera,
and the different manner in which they capture insects, will be
compared. [page 321]




CHAPTER XIV.
ALDROVANDA VESICULOSA.


Captures crustaceans—Structure of the leaves in comparison with those
of Dionaea— Absorption by the glands, by the quadrifid processes, and
points on the infolded margins— Aldrovanda vesiculosa, var.
australis—Captures prey—Absorption of animal matter—Aldrovanda
vesiculosa, var. verticillata—Concluding remarks.


This plant may be called a miniature aquatic Dionaea. Stein discovered
in 1873 that the bilobed leaves, which are generally found closed in
Europe, open under a sufficiently high temperature, and, when touched,
suddenly close.* They re-expand in from 24 to 36 hours, but only, as it
appears, when inorganic objects are enclosed. The leaves sometimes
contain bubbles of air, and were formerly supposed to be bladders;
hence the specific name of vesiculosa. Stein observed that
water-insects were sometimes caught, and Prof. Cohn has recently found
within the leaves of naturally growing plants many kinds of crustaceans
and larvæ.** Plants which had been kept in filtered water were placed
by him in a vessel con-

* Since his original publication, Stein has found out that the
irritability of the leaves was observed by De Sassus, as recorded in
‘Bull. Bot. Soc. de France,’ in 1861. Delpino states in a paper
published in 1871 (‘Nuovo Giornale Bot. Ital.’ vol. iii. p. 174) that
“una quantit di chioccioline e di altri animalcoli acquatici” are
caught and suffocated by the leaves. I presume that chioccioline are
fresh-water molluscs. It would be interesting to know whether their
shells are at all corroded by the acid of the digestive secretion.


** I am greatly indebted to this distinguished naturalist for having
sent me a copy of his memoir on Aldrovanda, before its publication in
his ‘Beiträge zur Biologie der Pflanzen,’ drittes Heft, 1875, page 71.
[page 322]


taining numerous crustaceans of the genus Cypris, and next morning many
were found imprisoned and alive, still swimming about within the closed
leaves, but doomed to certain death.

Directly after reading Prof. Cohn’s memoir, I received through the
kindness of Dr. Hooker living plants from Germany. As I can add nothing
to Prof. Cohn’s excellent description, I will give only two
illustrations, one of a whorl of leaves copied from his work, and the
other of a leaf pressed flat open, drawn by my son Francis. I will,
however, append a few remarks on the differences between this plant and
Dionaea.

Aldrovanda is destitute of roots and floats freely in the water. The
leaves are arranged in whorls round the stem. Their broad petioles
terminate in from four to six rigid projections,* each tipped with a
stiff, short bristle. The bilobed leaf, with the midrib likewise tipped
with a bristle, stands in the midst of these projections, and is
evidently defended by them. The lobes are formed of very delicate
tissue, so as to be translucent; they open, according to Cohn, about as
much as the two valves of a living mussel-shell, therefore even less
than the lobes of Dionaea; and this must make the capture of aquatic
animals more easy. The outside of the leaves and the petioles are
covered with minute two-armed papillae, evidently answering to the
eight-rayed papillae of Dionaea.

Each lobe rather exceeds a semi-circle in convexity, and consists of
two very different concentric portions; the inner and lesser portion,
or that next to the midrib,

* There has been much discussion by botanists on the homological nature
of these projections. Dr. Nitschke (‘Bot. Zeitung,’ 1861, p. 146)
believes that they correspond with the fimbriated scale-like bodies
found at the bases of the petioles of Drosera. [page 323]


is slightly concave, and is formed, according to Cohn, of three layers
of cells. Its upper surface is studded with colourless glands like, but
more simple than, those of Dionaea; they are supported on distinct
footstalks, consisting of two rows of cells. The outer

FIG. 13. (Aldrovanda vesiculosa.) Upper figure, whorl of leaves (from
Prof. Cohn). Lower figure, leaf pressed flat open and greatly enlarged.

and broader portion of the lobe is flat and very thin, being formed of
only two layers of cells. Its upper surface does not bear any glands,
but, in their place, small quadrifid processes, each consisting of four
tapering projections, which rise from a common [page 324] prominence.
These processes are formed of very delicate membrane lined with a layer
of protoplasm; and they sometimes contain aggregated globules of
hyaline matter. Two of the slightly diverging arms are directed towards
the circumference, and two towards the midrib, forming together a sort
of Greek cross. Occasionally two of the arms are replaced by one, and
then the projection is trifid. We shall see in a future chapter that
these projections curiously resemble those found within the bladders of
Utricularia, more especially of Utricularia montana, although this
genus is not related to Aldrovanda.

A narrow rim of the broad flat exterior part of each lobe is turned
inwards, so that, when the lobes are closed, the exterior surfaces of
the infolded portions come into contact. The edge itself bears a row of
conical, flattened, transparent points with broad bases, like the
prickles on the stem of a bramble or Rubus. As the rim is infolded,
these points are directed towards the midrib, and they appear at first
as if they were adapted to prevent the escape of prey; but this can
hardly be their chief function, for they are composed of very delicate
and highly flexible membrane, which can be easily bent or quite doubled
back without being cracked. Nevertheless, the infolded rims, together
with the points, must somewhat interfere with the retrograde movement
of any small creature, as soon as the lobes begin to close. The
circumferential part of the leaf of Aldrovanda thus differs greatly
from that of Dionaea; nor can the points on the rim be considered as
homologous with the spikes round the leaves of Dionaea, as these latter
are prolongations of the blade, and not mere epidermic productions.
They appear also to serve for a widely different purpose. [page 325]

On the concave gland-bearing portion of the lobes, and especially on
the midrib, there are numerous, long, finely pointed hairs, which, as
Prof. Cohn remarks, there can be little doubt are sensitive to a touch,
and, when touched, cause the leaf to close. They are formed of two rows
of cells, or, according to Cohn, sometimes of four, and do not include
any vascular tissue. They differ also from the six sensitive filaments
of Dionaea in being colourless, and in having a medial as well as a
basal articulation. No doubt it is owing to these two articulations
that, notwithstanding their length, they escape being broken when the
lobes close.

The plants which I received during the early part of October from Kew
never opened their leaves, though subjected to a high temperature.
After examining the structure of some of them, I experimented on only
two, as I hoped that the plants would grow; and I now regret that I did
not sacrifice a greater number.

A leaf was cut open along the midrib, and the glands examined under a
high power. It was then placed in a few drops of an infusion of raw
meat. After 3 hrs. 20 m. there was no change, but when next examined
after 23 hrs. 20 m., the outer cells of the glands contained, instead
of limpid fluid, spherical masses of a granular substance, showing that
matter had been absorbed from the infusion. That these glands secrete a
fluid which dissolves or digests animal matter out of the bodies of the
creatures which the leaves capture, is also highly probable from the
analogy of Dionaea. If we may trust to the same analogy, the concave
and inner portions of the two lobes probably close together by a slow
movement, as soon as the glands have absorbed a slight amount of [page
326] already soluble animal matter. The included water would thus be
pressed out, and the secretion consequently not be too much diluted to
act. With respect to the quadrifid processes on the outer parts of the
lobes, I was not able to decide whether they had been acted on by the
infusion; for the lining of protoplasm was somewhat shrunk before they
were immersed. Many of the points on the infolded rims also had their
lining of protoplasm similarly shrunk, and contained spherical granules
of hyaline matter.

A solution of urea was next employed. This substance was chosen partly
because it is absorbed by the quadrifid processes and more especially
by the glands of Utricularia—a plant which, as we shall hereafter see,
feeds on decayed animal matter. As urea is one of the last products of
the chemical changes going on in the living body, it seems fitted to
represent the early stages of the decay of the dead body. I was also
led to try urea from a curious little fact mentioned by Prof. Cohn,
namely that when rather large crustaceans are caught between the
closing lobes, they are pressed so hard whilst making their escape that
they often void their sausage-shaped masses of excrement, which were
found within most of the leaves. These masses, no doubt, contain urea.
They would be left either on the broad outer surfaces of the lobes
where the quadrifids are situated, or within the closed concavity. In
the latter case, water charged with excrementitious and decaying matter
would be slowly forced outwards, and would bathe the quadrifids, if I
am right in believing that the concave lobes contract after a time like
those of Dionaea. Foul water would also be apt to ooze out at all
times, especially when bubbles of air were generated within the
concavity.

A leaf was cut open and examined, and the outer [page 327] cells of the
glands were found to contain only limpid fluid. Some of the quadrifids
included a few spherical granules, but several were transparent and
empty, and their positions were marked. This leaf was now immersed in a
little solution of one part of urea to 146 of water, or three grains to
the ounce. After 3 hrs. 40 m. there was no change either in the glands
or quadrifids; nor was there any certain change in the glands after 24
hrs.; so that, as far as one trial goes, urea does not act on them in
the same manner as an infusion of raw meat. It was different with the
quadrifids; for the lining of protoplasm, instead of presenting a
uniform texture, was now slightly shrunk, and exhibited in many places
minute, thickened, irregular, yellowish specks and ridges, exactly like
those which appear within the quadrifids of Utricularia when treated
with this same solution. Moreover, several of the quadrifids, which
were before empty, now contained moderately sized or very small, more
or less aggregated, globules of yellowish matter, as likewise occurs
under the same circumstances with Utricularia. Some of the points on
the infolded margins of the lobes were similarly affected; for their
lining of protoplasm was a little shrunk and included yellowish specks;
and those which were before empty now contained small spheres and
irregular masses of hyaline matter, more or less aggregated; so that
both the points on the margins and the quadrifids had absorbed matter
from the solution in the course of 24 hrs.; but to this subject I shall
recur. In another rather old leaf, to which nothing had been given, but
which had been kept in foul water, some of the quadrifids contained
aggregated translucent globules. These were not acted on by a solution
of one part of carbonate of ammonia to 218 of water; and this negative
result [page 328] agrees with what I have observed under similar
circumstances with Utricularia.

Aldrovanda vesiculosa, var. australis.—Dried leaves of this plant from
Queensland in Australia were sent me by Prof. Oliver from the herbarium
at Kew. Whether it ought to be considered as a distinct species or a
variety, cannot be told until the flowers are examined by a botanist.
The projections at the upper end of the petiole (from four to six in
number) are considerably longer relatively to the blade, and much more
attenuated than those of the European form. They are thickly covered
for a considerable space near their extremities with the upcurved
prickles, which are quite absent in the latter form; and they generally
bear on their tips two or three straight prickles instead of one. The
bilobed leaf appears also to be rather larger and somewhat broader,
with the pedicel by which it is attached to the upper end of the
petiole a little longer. The points on the infolded margins likewise
differ; they have narrower bases, and are more pointed; long and short
points also alternate with much more regularity than in the European
form. The glands and sensitive hairs are similar in the two forms. No
quadrifid processes could be seen on several of the leaves, but I do
not doubt that they were present, though indistinguishable from their
delicacy and from having shrivelled; for they were quite distinct on
one leaf under circumstances presently to be mentioned.

Some of the closed leaves contained no prey, but in one there was a
rather large beetle, which from its flattened tibiae I suppose was an
aquatic species, but was not allied to Colymbetes. All the softer
tissues of this beetle were completely dissolved, and its chitinous
integuments were as clean as if they had been [page 329] boiled in
caustic potash; so that it must have been enclosed for a considerable
time. The glands were browner and more opaque than those on other
leaves which had caught nothing; and the quadrifid processes, from
being partly filled with brown granular matter, could be plainly
distinguished, which was not the case, as already stated, on the other
leaves. Some of the points on the infolded margins likewise contained
brownish granular matter. We thus gain additional evidence that the
glands, the quadrifid processes, and the marginal points, all have the
power of absorbing matter, though probably of a different nature.

Within another leaf disintegrated remnants of a rather small animal,
not a crustacean, which had simple, strong, opaque mandibles, and a
large unarticulated chitinous coat, were present. Lumps of black
organic matter, possibly of a vegetable nature, were enclosed in two
other leaves; but in one of these there was also a small worm much
decayed. But the nature of partially digested and decayed bodies, which
have been pressed flat, long dried, and then soaked in water, cannot be
recognised easily. All the leaves contained unicellular and other
Algae, still of a greenish colour, which had evidently lived as
intruders, in the same manner as occurs, according to Cohn, within the
leaves of this plant in Germany.

Aldrovanda vesiculosa, var. verticillata.—Dr. King, Superintendent of
the Botanic Gardens, kindly sent me dried specimens collected near
Calcutta. This form was, I believe, considered by Wallich as a distinct
species, under the name of verticillata. It resembles the Australian
form much more nearly than the European; namely in the projections at
the upper end of the petiole being much attenuated and covered with
[page 330] upcurved prickles; they terminate also in two straight
little prickles. The bilobed leaves are, I believe, larger and
certainly broader even than those of the Australian form; so that the
greater convexity of their margins was conspicuous. The length of an
open leaf being taken at 100, the breadth of the Bengal form is nearly
173, of the Australian form 147, and of the German 134. The points on
the infolded margins are like those in the Australian form. Of the few
leaves which were examined, three contained entomostracan crustaceans.

Concluding Remarks.—The leaves of the three foregoing closely allied
species or varieties are manifestly adapted for catching living
creatures. With respect to the functions of the several parts, there
can be little doubt that the long jointed hairs are sensitive, like
those of Dionaea, and that, when touched, they cause the lobes to
close. That the glands secrete a true digestive fluid and afterwards
absorb the digested matter, is highly probable from the analogy of
Dionaea,—from the limpid fluid within their cells being aggregated into
spherical masses, after they had absorbed an infusion of raw meat,—from
their opaque and granular condition in the leaf, which had enclosed a
beetle for a long time,—and from the clean condition of the integuments
of this insect, as well as of crustaceans (as described by Cohn), which
have been long captured. Again, from the effect produced on the
quadrifid processes by an immersion for 24 hrs. in a solution of
urea,—from the presence of brown granular matter within the quadrifids
of the leaf in which the beetle had been caught,—and from the analogy
of Utricularia,—it is probable that these processes absorb
excrementitious and decaying animal matter. It is a more curious fact
that the points on [page 331] the infolded margins apparently serve to
absorb decayed animal matter in the same manner as the quadrifids. We
can thus understand the meaning of the infolded margins of the lobes
furnished with delicate points directed inwards, and of the broad,
flat, outer portions, bearing quadrifid processes; for these surfaces
must be liable to be irrigated by foul water flowing from the concavity
of the leaf when it contains dead animals. This would follow from
various causes,—from the gradual contraction of the concavity,—from
fluid in excess being secreted,—and from the generation of bubbles of
air. More observations are requisite on this head; but if this view is
correct, we have the remarkable case of different parts of the same
leaf serving for very different purposes—one part for true digestion,
and another for the absorption of decayed animal matter. We can thus
also understand how, by the gradual loss of either power, a plant might
be gradually adapted for the one function to the exclusion of the
other; and it will hereafter be shown that two genera, namely
Pinguicula and Utricularia, belonging to the same family, have been
adapted for these two different functions. [page 332]




CHAPTER XV.
DROSOPHYLLUM—RORIDULA—BYBLIS—GLANDULAR HAIRS OF OTHER PLANTS—CONCLUDING
REMARKS ON THE DROSERACEÆ.


Drosophyllum—Structure of leaves—Nature of the secretion—Manner of
catching insects— Power of absorption—Digestion of animal
substances—Summary on Drosophyllum—Roridula—Byblis—Glandular hairs of
other plants, their power of absorption—Saxifraga—Primula—
Pelargonium—Erica—Mirabilis—Nicotiana—Summary on glandular
hairs—Concluding remarks on the Droseraceae.


Drosophyllum lusitanicum.—This rare plant has been found only in
Portugal, and, as I hear from Dr. Hooker, in Morocco. I obtained living
specimens through the great kindness of Mr. W.C. Tait, and afterwards
from Mr. G. Maw and Dr. Moore. Mr. Tait informs me that it grows
plentifully on the sides of dry hills near Oporto, and that vast
numbers of flies adhere to the leaves. This latter fact is well-known
to the villagers, who call the plant the “fly-catcher,” and hang it up
in their cottages for this purpose. A plant in my hot-house caught so
many insects during the early part of April, although the weather was
cold and insects scarce, that it must have been in some manner strongly
attractive to them. On four leaves of a young and small plant, 8, 10,
14, and 16 minute insects, chiefly Diptera, were found in the autumn
adhering to them. I neglected to examine the roots, but I hear from Dr.
Hooker that they are very small, as in the case of the previously
mentioned members of the same family of the Droseraceae.

The leaves arise from an almost woody axis; they [page 333] are linear,
much attenuated towards their tips, and several inches in length. The
upper surface is concave, the lower convex, with a narrow channel down
the middle. Both surfaces, with the exception of the channel, are
covered with glands, supported on pedicels and arranged in irregular
longitudinal rows. These organs I shall call tentacles, from their
close resemblance to those of Drosera, though they have no power of
movement. Those on the same leaf differ much in length. The glands also
differ in size, and are of a bright pink or of a purple colour; their
upper surfaces are convex, and the lower flat or even concave, so that
they resemble miniature mushrooms in appearance. They are formed of two
(as I believe) layers of delicate angular cells, enclosing eight or ten
larger cells with thicker, zigzag walls. Within these larger cells
there are others marked by spiral lines, and apparently connected with
the spiral vessels which run up the green multi-cellular pedicels. The
glands secrete large drops of viscid secretion. Other glands, having
the same general appearance, are found on the flower-peduncles and
calyx.

FIG. 14. (Drosophyllum lusitanicum.) Part of leaf, enlarged seven
times, showing lower surface.

Besides the glands which are borne on longer or shorter pedicels, there
are numerous ones, both on the upper and lower surfaces of the leaves,
so small as to be scarcely visible to the naked eye. They are
colourless and almost sessile, either circular or oval in outline; the
latter occurring chiefly on the backs of the leaves (fig. 14).
Internally they have exactly the same structure as the larger glands
which are supported on pedicels; [page 334] and indeed the two sets
almost graduate into one another. But the sessile glands differ in one
important respect, for they never secrete spontaneously, as far as I
have seen, though I have examined them under a high power on a hot day,
whilst the glands on pedicels were secreting copiously. Nevertheless,
if little bits of damp albumen or fibrin are placed on these sessile
glands, they begin after a time to secrete, in the same manner as do
the glands of Dionaea when similarly treated. When they were merely
rubbed with a bit of raw meat, I believe that they likewise secreted.
Both the sessile glands and the taller ones on pedicels have the power
of rapidly absorbing nitrogenous matter.

The secretion from the taller glands differs in a remarkable manner
from that of Drosera, in being acid before the glands have been in any
way excited; and judging from the changed colour of litmus paper, more
strongly acid than that of Drosera. This fact was observed repeatedly;
on one occasion I chose a young leaf, which was not secreting freely,
and had never caught an insect, yet the secretion on all the glands
coloured litmus paper of a bright red. From the quickness with which
the glands are able to obtain animal matter from such substances as
well-washed fibrin and cartilage, I suspect that a small quantity of
the proper ferment must be present in the secretion before the glands
are excited, so that a little animal matter is quickly dissolved.

Owing to the nature of the secretion or to the shape of the glands, the
drops are removed from them with singular facility. It is even somewhat
difficult, by the aid of a finely pointed polished needle, slightly
damped with water, to place a minute particle of any kind on one of the
drops; for on withdrawing the [page 335] needle, the drop is generally
withdrawn; whereas with Drosera there is no such difficulty, though the
drops are occasionally withdrawn. From this peculiarity, when a small
insect alights on a leaf of Drosophyllum, the drops adhere to its
wings, feet, or body, and are drawn from the gland; the insect then
crawls onward and other drops adhere to it; so that at last, bathed by
the viscid secretion, it sinks down and dies, resting on the small
sessile glands with which the surface of the leaf is thickly covered.
In the case of Drosera, an insect sticking to one or more of the
exterior glands is carried by their movement to the centre of the leaf;
with Drosophyllum, this is effected by the crawling of the insect, as
from its wings being clogged by the secretion it cannot fly away.

There is another difference in function between the glands of these two
plants: we know that the glands of Drosera secrete more copiously when
properly excited. But when minute particles of carbonate of ammonia,
drops of a solution of this salt or of the nitrate of ammonia, saliva,
small insects, bits of raw or roast meat, albumen, fibrin or cartilage,
as well as inorganic particles, were placed on the glands of
Drosophyllum, the amount of secretion never appeared to be in the least
increased. As insects do not commonly adhere to the taller glands, but
withdraw the secretion, we can see that there would be little use in
their having acquired the habit of secreting copiously when stimulated;
whereas with Drosera this is of use, and the habit has been acquired.
Nevertheless, the glands of Drosophyllum, without being stimulated,
continually secrete, so as to replace the loss by evaporation. Thus
when a plant was placed under a small bell-glass with its inner surface
and support thoroughly wetted, there was no loss by evaporation, and so
much [page 336] secretion was accumulated in the course of a day that
it ran down the tentacles and covered large spaces of the leaves.

The glands to which the above named nitrogenous substances and liquids
were given did not, as just stated, secrete more copiously; on the
contrary, they absorbed their own drops of secretion with surprising
quickness. Bits of damp fibrin were placed on five glands, and when
they were looked at after an interval of 1 hr. 12 m., the fibrin was
almost dry, the secretion having been all absorbed. So it was with
three cubes of albumen after 1 hr. 19 m., and with four other cubes,
though these latter were not looked at until 2 hrs. 15 m. had elapsed.
The same result followed in between 1 hr. 15 m. and 1 hr. 30 m. when
particles both of cartilage and meat were placed on several glands.
Lastly, a minute drop (about 1/20 of a minim) of a solution of one part
of nitrate of ammonia to 146 of water was distributed between the
secretion surrounding three glands, so that the amount of fluid
surrounding each was slightly increased; yet when looked at after 2
hrs., all three were dry. On the other hand, seven particles of glass
and three of coal-cinders, of nearly the same size as those of the
above named organic substances, were placed on ten glands; some of them
being observed for 18 hrs., and others for two or three days; but there
was not the least sign of the secretion being absorbed. Hence, in the
former cases, the absorption of the secretion must have been due to the
presence of some nitrogenous matter, which was either already soluble
or was rendered so by the secretion. As the fibrin was pure, and had
been well washed in distilled water after being kept in glycerine, and
as the cartilage had been soaked in water, I suspect that these
substances must [page 337] have been slightly acted on and rendered
soluble within the above stated short periods.

The glands have not only the power of rapid absorption, but likewise of
secreting again quickly; and this latter habit has perhaps been gained,
inasmuch as insects, if they touch the glands, generally withdraw the
drops of secretion, which have to be restored. The exact period of
re-secretion was recorded in only a few cases. The glands on which bits
of meat were placed, and which were nearly dry after about 1 hr. 30 m.,
when looked at after 22 additional hours, were found secreting; so it
was after 24 hrs. with one gland on which a bit of albumen had been
placed. The three glands to which a minute drop of a solution of
nitrate of ammonia was distributed, and which became dry after 2 hrs.,
were beginning to re-secrete after only 12 additional hours.

Tentacles Incapable of Movement.—Many of the tall tentacles, with
insects adhering to them, were carefully observed; and fragments of
insects, bits of raw meat, albumen, &c., drops of a solution of two
salts of ammonia and of saliva, were placed on the glands of many
tentacles; but not a trace of movement could ever be detected. I also
repeatedly irritated the glands with a needle, and scratched and
pricked the blades, but neither the blade nor the tentacles became at
all inflected. We may therefore conclude that they are incapable of
movement.

On the Power of Absorption possessed by the Glands.—It has already been
indirectly shown that the glands on pedicels absorb animal matter; and
this is further shown by their changed colour, and by the aggregation
of their contents, after they have been left in contact with
nitrogenous substances or liquids. The following observations apply
both to the glands supported on [page 338] pedicels and to the minute
sessile ones. Before a gland has been in any way stimulated, the
exterior cells commonly contain only limpid purple fluid; the more
central ones including mulberry-like masses of purple granular matter.
A leaf was placed in a little solution of one part of carbonate of
ammonia to 146 of water (3 grs. to 1 oz.), and the glands were
instantly darkened and very soon became black; this change being due to
the strongly marked aggregation of their contents, more especially of
the inner cells. Another leaf was placed in a solution of the same
strength of nitrate of ammonia, and the glands were slightly darkened
in 25 m., more so in 50 m., and after 1 hr. 30 m. were of so dark a red
as to appear almost black. Other leaves were placed in a weak infusion
of raw meat and in human saliva, and the glands were much darkened in
25 m., and after 40 m. were so dark as almost to deserve to be called
black. Even immersion for a whole day in distilled water occasionally
induces some aggregation within the glands, so that they become of a
darker tint. In all these cases the glands are affected in exactly the
same manner as those of Drosera. Milk, however, which acts so
energetically on Drosera, seems rather less effective on Drosophyllum,
for the glands were only slightly darkened by an immersion of 1 hr. 20
m., but became decidedly darker after 3 hrs. Leaves which had been left
for 7 hrs. in an infusion of raw meat or in saliva were placed in the
solution of carbonate of ammonia, and the glands now became greenish;
whereas, if they had been first placed in the carbonate, they would
have become black. In this latter case, the ammonia probably combines
with the acid of the secretion, and therefore does not act on the
colouring matter; but when the glands are first subjected to an organic
[page 339] fluid, either the acid is consumed in the work of digestion
or the cell-walls are rendered more permeable, so that the undecomposed
carbonate enters and acts on the colouring matter. If a particle of the
dry carbonate is placed on a gland, the purple colour is quickly
discharged, owing probably to an excess of the salt. The gland,
moreover, is killed.

Turning now to the action of organic substances, the glands on which
bits of raw meat were placed became dark-coloured; and in 18 hrs. their
contents were conspicuously aggregated. Several glands with bits of
albumen and fibrin were darkened in between 2 hrs. and 3 hrs.; but in
one case the purple colour was completely discharged. Some glands which
had caught flies were compared with others close by; and though they
did not differ much in colour, there was a marked difference in their
state of aggregation. In some few instances, however, there was no such
difference, and this appeared to be due to the insects having been
caught long ago, so that the glands had recovered their pristine state.
In one case, a group of the sessile colourless glands, to which a small
fly adhered, presented a peculiar appearance; for they had become
purple, owing to purple granular matter coating the cell-walls. I may
here mention as a caution that, soon after some of my plants arrived in
the spring from Portugal, the glands were not plainly acted on by bits
of meat, or insects, or a solution of ammonia—a circumstance for which
I cannot account.

Digestion of Solid Animal Matter.—Whilst I was trying to place on two
of the taller glands little cubes of albumen, these slipped down, and,
besmeared with secretion, were left resting on some of the small
sessile glands. After 24 hrs. one of these cubes was found [page 340]
completely liquefied, but with a few white streaks still visible; the
other was much rounded, but not quite dissolved. Two other cubes were
left on tall glands for 2 hrs. 45 m., by which time all the secretion
was absorbed; but they were not perceptibly acted on, though no doubt
some slight amount of animal matter had been absorbed from them. They
were then placed on the small sessile glands, which being thus
stimulated secreted copiously in the course of 7 hrs. One of these
cubes was much liquefied within this short time; and both were
completely liquefied after 21 hrs. 15 m.; the little liquid masses,
however, still showing some white streaks. These streaks disappeared
after an additional period of 6 hrs. 30 m.; and by next morning (i.e.
48 hrs. from the time when the cubes were first placed on the glands)
the liquefied matter was wholly absorbed. A cube of albumen was left on
another tall gland, which first absorbed the secretion and after 24
hrs. poured forth a fresh supply. This cube, now surrounded by
secretion, was left on the gland for an additional 24 hrs., but was
very little, if at all, acted on. We may, therefore, conclude, either
that the secretion from the tall glands has little power of digestion,
though strongly acid, or that the amount poured forth from a single
gland is insufficient to dissolve a particle of albumen which within
the same time would have been dissolved by the secretion from several
of the small sessile glands. Owing to the death of my last plant, I was
unable to ascertain which of these alternatives is the true one.

Four minute shreds of pure fibrin were placed, each resting on one,
two, or three of the taller glands. In the course of 2 hrs. 30 m. the
secretion was all absorbed, and the shreds were left almost dry. They
[page 341] were then pushed on to the sessile glands. One shred, after
2 hrs. 30 m., seemed quite dissolved, but this may have been a mistake.
A second, when examined after 17 hrs. 25 m., was liquefied, but the
liquid as seen under the microscope still contained floating granules
of fibrin. The other two shreds were completely liquefied after 21 hrs.
30 m.; but in one of the drops a very few granules could still be
detected. These, however, were dissolved after an additional interval
of 6 hrs. 30 m.; and the surface of the leaf for some distance all
round was covered with limpid fluid. It thus appears that Drosophyllum
digests albumen and fibrin rather more quickly than Drosera can; and
this may perhaps be attributed to the acid, together probably with some
small amount of the ferment, being present in the secretion, before the
glands have been stimulated; so that digestion begins at once.

Concluding Remarks.—The linear leaves of Drosophyllum differ but
slightly from those of certain species of Drosera; the chief
differences being, firstly, the presence of minute, almost sessile,
glands, which, like those of Dionaea, do not secrete until they are
excited by the absorption of nitrogenous matter. But glands of this
kind are present on the leaves of Drosera binata, and appear to be
represented by the papillae on the leaves of Drosera rotundifolia.
Secondly, the presence of tentacles on the backs of the leaves; but we
have seen that a few tentacles, irregularly placed and tending towards
abortion, are retained on the backs of the leaves of Drosera binata.
There are greater differences in function between the two genera. The
most important one is that the tentacles of Drosophyllum have no power
of movement; this loss being partially replaced by the drops of viscid
[page 342] secretion being readily withdrawn from the glands; so that,
when an insect comes into contact with a drop, it is able to crawl
away, but soon touches other drops, and then, smothered by the
secretion, sinks down on the sessile glands and dies. Another
difference is, that the secretion from the tall glands, before they
have been in any way excited, is strongly acid, and perhaps contains a
small quantity of the proper ferment. Again, these glands do not
secrete more copiously from being excited by the absorption of
nitrogenous matter; on the contrary, they then absorb their own
secretion with extraordinary quickness. In a short time they begin to
secrete again. All these circumstances are probably connected with the
fact that insects do not commonly adhere to the glands with which they
first come into contact, though this does sometimes occur; and that it
is chiefly the secretion from the sessile glands which dissolves animal
matter out of their bodies.

RORIDULA.


Roridula dentata.—This plant, a native of the western parts of the Cape
of Good Hope, was sent to me in a dried state from Kew. It has an
almost woody stem and branches, and apparently grows to a height of
some feet. The leaves are linear, with their summits much attenuated.
Their upper and lower surfaces are concave, with a ridge in the middle,
and both are covered with tentacles, which differ greatly in length;
some being very long, especially those on the tips of the leaves, and
some very short. The glands also differ much in size and are somewhat
elongated. They are supported on multicellular pedicels.

This plant, therefore, agrees in several respects with [page 343]
Drosophyllum, but differs in the following points. I could detect no
sessile glands; nor would these have been of any use, as the upper
surface of the leaves is thickly clothed with pointed, unicellular
hairs directed upwards. The pedicels of the tentacles do not include
spiral vessels; nor are there any spiral cells within the glands. The
leaves often arise in tufts and are pinnatifid, the divisions
projecting at right angles to the main linear blade. These lateral
divisions are often very short and bear only a single terminal
tentacle, with one or two short ones on the sides. No distinct line of
demarcation can be drawn between the pedicels of the long terminal
tentacles and the much attenuated summits of the leaves. We may,
indeed, arbitrarily fix on the point to which the spiral vessels
proceeding from the blade extend; but there is no other distinction.

It was evident from the many particles of dirt sticking to the glands
that they secrete much viscid matter. A large number of insects of many
kinds also adhered to the leaves. I could nowhere discover any signs of
the tentacles having been inflected over the captured insects; and this
probably would have been seen even in the dried specimens, had they
possessed the power of movement. Hence, in this negative character,
Roridula resembles its northern representative, Drosophyllum.

BYBLIS.


Byblis gigantea (Western Australia).—A dried specimen, about 18 inches
in height, with a strong stem, was sent me from Kew. The leaves are
some inches in length, linear, slightly flattened, with a small
projecting rib on the lower surface. They are covered on all sides by
glands of two kinds [page 344] —sessile ones arranged in rows, and
others supported on moderately long pedicels. Towards the narrow
summits of the leaves the pedicels are longer than elsewhere, and here
equal the diameter of the leaf. The glands are purplish, much
flattened, and formed of a single layer of radiating cells, which in
the larger glands are from forty to fifty in number. The pedicels
consist of single elongated cells, with colourless, extremely delicate
walls, marked with the finest intersecting spiral lines. Whether these
lines are the result of contraction from the drying of the walls, I do
not know, but the whole pedicel was often spirally rolled up. These
glandular hairs are far more simple in structure than the so-called
tentacles of the preceding genera, and they do not differ essentially
from those borne by innumerable other plants. The flower-peduncles bear
similar glands. The most singular character about the leaves is that
the apex is enlarged into a little knob, covered with glands, and about
a third broader than the adjoining part of the attenuated leaf. In two
places dead flies adhered to the glands. As no instance is known of
unicellular structures having any power of movement,* Byblis, no doubt,
catches insects solely by the aid of its viscid secretion. These
probably sink down besmeared with the secretion and rest on the small
sessile glands, which, if we may judge by the analogy of Drosophyllum,
then pour forth their secretion and afterwards absorb the digested
matter.

Supplementary Observations on the Power of Absorption by the Glandular
Hairs of other Plants.—A few observations on this subject may be here
conveniently introduced. As the glands of many, probably of all,

* Sachs, ‘Traité de Bot.,’ 3rd edit. 1874, p. 1026. [page 345]


the species of Droseraceae absorb fluids or at least allow them readily
to enter,* it seemed desirable to ascertain how far the glands of other
plants which are not specially adapted for capturing insects, had the
same power. Plants were chosen for trial at hazard, with the exception
of two species of saxifrage, which were selected from belonging to a
family allied to the Droseraceae. Most of the experiments were made by
immersing the glands either in an infusion of raw meat or more commonly
in a solution of carbonate of ammonia, as this latter substance acts so
powerfully and rapidly on protoplasm. It seemed also particularly
desirable to ascertain whether ammonia was absorbed, as a small amount
is contained in rain-water. With the Droseraceae the secretion of a
viscid fluid by the glands does not prevent their absorbing; so that
the glands of other plants might excrete superfluous matter, or secrete
an odoriferous fluid as a protection against the attacks of insects, or
for any other purpose, and yet have the power of absorbing. I regret
that in the following cases I did not try whether the secretion could
digest or render soluble animal substances, but such experiments would
have been difficult on account of the small size of the glands and the
small amount of secretion. We shall see in the next chapter that the
secretion from the glandular hairs of Pinguicula certainly dissolves
animal matter.

[Saxifraga umbrosa.—The flower-peduncles and petioles of the leaves are
clothed with short hairs, bearing pink-coloured glands, formed of
several polygonal cells, with their pedicels divided by partitions into
distinct cells, which are generally colourless, but sometimes pink. The
glands secrete a yellowish viscid fluid, by

* The distinction between true absorption and mere permeation, or
imbibition, is by no means clearly understood: see Müller’s
‘Physiology,’ Eng. translat. 1838, vol. i. p. 280. [page 346]


which minute Diptera are sometimes, though not often, caught.* The
cells of the glands contain bright pink fluid, charged with granules or
with globular masses of pinkish pulpy matter. This matter must be
protoplasm, for it is seen to undergo slow but incessant changes of
form if a gland be placed in a drop of water and examined. Similar
movements were observed after glands had been immersed in water for 1,
3, 5, 18, and 27 hrs. Even after this latter period the glands retained
their bright pink colour; and the protoplasm within their cells did not
appear to have become more aggregated. The continually changing forms
of the little masses of protoplasm are not due to the absorption of
water, as they were seen in glands kept dry.

A flower-stem, still attached to a plant, was bent (May 29) so as to
remain immersed for 23 hrs. 30 m. in a strong infusion of raw meat. The
colour of the contents of the glands was slightly changed, being now of
a duller and more purple tint than before. The contents also appeared
more aggregated, for the spaces between the little masses of protoplasm
were wider; but this latter result did not follow in some other and
similar experiments. The masses seemed to change their forms more
rapidly than did those in water; so that the cells had a different
appearance every four or five minutes. Elongated masses became in the
course of one or two minutes spherical; and spherical ones drew
themselves out and united with others. Minute masses rapidly increased
in size, and three distinct ones were seen to unite. The movements
were, in short, exactly like those described in the case of Drosera.
The cells of the pedicels were not affected by the infusion; nor were
they in the following experiment.

Another flower-stem was placed in the same manner and for the same
length of time in a solution of one part of nitrate of ammonia to 146
of water (or 3 grs. to 1 oz.), and the glands were discoloured in
exactly the same manner as by the infusion of raw meat.

Another flower-stem was immersed, as before, in a solution of one part
of carbonate of ammonia to 109 of water. The glands, after 1 hr. 30 m.,
were not discoloured, but after 3 hrs. 45 m. most of them had become
dull purple, some of them blackish-

* In the case of Saxifraga tridactylites, Mr. Druce says
(‘Pharmaceutical Journal,’ May 1875) that he examined some dozens of
plants, and in almost every instance remnants of insects adhered to the
leaves. So it is, as I hear from a friend, with this plant in Ireland.
[page 347]


green, a few being still unaffected. The little masses of protoplasm
within the cells were seen in movement. The cells of the pedicels were
unaltered. The experiment was repeated, and a fresh flower-stem was
left for 23 hrs. in the solution, and now a great effect was produced;
all the glands were much blackened, and the previously transparent
fluid in the cells of the pedicels, even down to their bases, contained
spherical masses of granular matter. By comparing many different hairs,
it was evident that the glands first absorb the carbonate, and that the
effect thus produced travels down the hairs from cell to cell. The
first change which could be observed is a cloudy appearance in the
fluid, due to the formation of very fine granules, which afterwards
aggregate into larger masses. Altogether, in the darkening of the
glands, and in the process of aggregation travelling down the cells of
the pedicels, there is the closest resemblance to what takes place when
a tentacle of Drosera is immersed in a weak solution of the same salt.
The glands, however, absorb very much more slowly than those of
Drosera. Besides the glandular hairs, there are star-shaped organs
which do not appear to secrete, and which were not in the least
affected by the above solutions.

Although in the case of uninjured flower-stems and leaves the carbonate
seems to be absorbed only by the glands, yet it enters a cut surface
much more quickly than a gland. Strips of the rind of a flower-stem
were torn off, and the cells of the pedicels were seen to contain only
colourless transparent fluid; those of the glands including as usual
some granular matter. These strips were then immersed in the same
solution as before (one part of the carbonate to 109 of water), and in
a few minutes granular matter appeared in the lowercells of all the
pedicels. The action invariably commenced (for I tried the experiment
repeatedly) in the lowest cells, and therefore close to the torn
surface, and then gradually travelled up the hairs until it reached the
glands, in a reversed direction to what occurs in uninjured specimens.
The glands then became discoloured, and the previously contained
granular matter was aggregated into larger masses. Two short bits of a
flower-stem were also left for 2 hrs. 40 m. in a weaker solution of one
part of the carbonate to 218 of water; and in both specimens the
pedicels of the hairs near the cut ends now contained much granular
matter; and the glands were completely discoloured.

Lastly, bits of meat were placed on some glands; these were examined
after 23 hrs., as were others, which had apparently not long before
caught minute flies; but they did not present any [page 348] difference
from the glands of other hairs. Perhaps there may not have been time
enough for absorption. I think so as some glands, on which dead flies
had evidently long lain, were of a pale dirty purple colour or even
almost colourless, and the granular matter within them presented an
unusual and somewhat peculiar appearance. That these glands had
absorbed animal matter from the flies, probably by exosmose into the
viscid secretion, we may infer, not only from their changed colour, but
because, when placed in a solution of carbonate of ammonia, some of the
cells in their pedicels become filled with granular matter; whereas the
cells of other hairs, which had not caught flies, after being treated
with the same solution for the same length of time, contained only a
small quantity of granular matter. But more evidence is necessary
before we fully admit that the glands of this saxifrage can absorb,
even with ample time allowed, animal matter from the minute insects
which they occasionally and accidentally capture.

Saxifraga rotundifolia (?).—The hairs on the flower-stems of this
species are longer than those just described, and bear pale brown
glands. Many were examined, and the cells of the pedicels were quite
transparent. A bent stem was immersed for 30 m. in a solution of one
part of carbonate of ammonia to 109 of water, and two or three of the
uppermost cells in the pedicels now contained granular or aggregated
matter; the glands having become of a bright yellowish-green. The
glands of this species therefore absorb the carbonate much more quickly
than do those of Saxifraga umbrosa, and the upper cells of the pedicels
are likewise affected much more quickly. Pieces of the stem were cut
off and immersed in the same solution; and now the process of
aggregation travelled up the hairs in a reversed direction; the cells
close to the cut surfaces being first affected.

Primula sinensis.—The flower-stems, the upper and lower surfaces of the
leaves and their footstalks, are all clothed with a multitude of longer
and shorter hairs. The pedicels of the longer hairs are divided by
transverse partitions into eight or nine cells. The enlarged terminal
cell is globular, forming a gland which secretes a variable amount of
thick, slightly viscid, not acid, brownish-yellow matter.

A piece of a young flower-stem was first immersed in distilled water
for 2 hrs. 30 m., and the glandular hairs were not at all affected.
Another piece, bearing twenty-five short and nine long hairs, was
carefully examined. The glands of the latter contained no solid or
semi-solid matter; and those of only two [page 349] of the twenty-five
short hairs contained some globules. This piece was then immersed for 2
hrs. in a solution of one part of carbonate of ammonia to 109 of water,
and now the glands of the twenty-five shorter hairs, with two or three
exceptions, contained either one large or from two to five smaller
spherical masses of semi-solid matter. Three of the glands of the nine
long hairs likewise included similar masses. In a few hairs there were
also globules in the cells immediately beneath the glands. Looking to
all thirty-four hairs, there could be no doubt that the glands had
absorbed some of the carbonate. Another piece was left for only 1 hr.
in the same solution, and aggregated matter appeared in all the glands.
My son Francis examined some glands of the longer hairs, which
contained little masses of matter, before they were immersed in any
solution; and these masses slowly changed their forms, so that no doubt
they consisted of protoplasm. He then irrigated these hairs for 1 hr.
15 m., whilst under the microscope, with a solution of one part of the
carbonate to 218 of water; the glands were not perceptibly affected,
nor could this have been expected, as their contents were already
aggregated. But in the cells of the pedicels numerous, almost
colourless, spheres of matter appeared, which changed their forms and
slowly coalesced; the appearance of the cells being thus totally
changed at successive intervals of time.

The glands on a young flower-stem, after having been left for 2 hrs. 45
m. in a strong solution of one part of the carbonate to 109 of water,
contained an abundance of aggregated masses, but whether generated by
the action of the salt, I do not know. This piece was again placed in
the solution, so that it was immersed altogether for 6 hrs. 15 m., and
now there was a great change; for almost all the spherical masses
within the gland-cells had disappeared, being replaced by granular
matter of a darker brown. The experiment was thrice repeated with
nearly the same result. On one occasion the piece was left immersed for
8 hrs. 30 m., and though almost all the spherical masses were changed
into the brown granular matter, a few still remained. If the spherical
masses of aggregated matter had been originally produced merely by some
chemical or physical action, it seems strange that a somewhat longer
immersion in the same solution should so completely alter their
character. But as the masses which slowly and spontaneously changed
their forms must have consisted of living protoplasm, there is nothing
surprising in its being injured or killed, and its appearance wholly
changed by long immersion in so strong a solution of the carbonate as
that [page 350] employed. A solution of this strength paralyses all
movement in Drosera, but does not kill the protoplasm; a still stronger
solution prevents the protoplasm from aggregating into the ordinary
full-sized globular masses, and these, though they do not disintegrate,
become granular and opaque. In nearly the same manner, too hot water
and certain solutions (for instance, of the salts of soda and potash)
cause at first an imperfect kind of aggregation in the cells of
Drosera; the little masses afterwards breaking up into granular or
pulpy brown matter. All the foregoing experiments were made on
flower-stems, but a piece of a leaf was immersed for 30 m. in a strong
solution of the carbonate (one part to 109 of water), and little
globular masses of matter appeared in all the glands, which before
contained only limpid fluid.

I made also several experiments on the action of the vapour of the
carbonate on the glands; but will give only a few cases. The cut end of
the footstalk of a young leaf was protected with sealing-wax, and was
then placed under a small bell-glass, with a large pinch of the
carbonate. After 10 m. the glands showed a considerable degree of
aggregation, and the protoplasm lining the cells of the pedicels was a
little separated from the walls. Another leaf was left for 50 m. with
the same result, excepting that the hairs became throughout their whole
length of a brownish colour. In a third leaf, which was exposed for 1
hr. 50 m., there was much aggregated matter in the glands; and some of
the masses showed signs of breaking up into brown granular matter. This
leaf was again placed in the vapour, so that it was exposed altogether
for 5 hrs. 30 m.; and now, though I examined a large number of glands,
aggregated masses were found in only two or three; in all the others,
the masses, which before had been globular, were converted into brown,
opaque, granular matter. We thus see that exposure to the vapour for a
considerable time produces the same effects as long immersion in a
strong solution. In both cases there could hardly be a doubt that the
salt had been absorbed chiefly or exclusively by the glands.

On another occasion bits of damp fibrin, drops of a weak infusion of
raw meat and of water, were left for 24 hrs. on some leaves; the hairs
were then examined, but to my surprise differed in no respect from
others which had not been touched by these fluids. Most of the cells,
however, included hyaline, motionless little spheres, which did not
seem to consist of protoplasm, but, I suppose, of some balsam or
essential oil.

Pelargonium zonale (var. edged with white).—The leaves [page 351] are
clothed with numerous multicellular hairs; some simply pointed; others
bearing glandular heads, and differing much in length. The glands on a
piece of leaf were examined and found to contain only limpid fluid;
most of the water was removed from beneath the covering glass, and a
minute drop of one part of carbonate of ammonia to 146 of water was
added; so that an extremely small dose was given. After an interval of
only 3 m. there were signs of aggregation within the glands of the
shorter hairs; and after 5 m. many small globules of a pale brown tint
appeared in all of them; similar globules, but larger, being found in
the large glands of the longer hairs. After the specimen had been left
for 1 hr. in the solution, many of the smaller globules had changed
their positions; and two or three vacuoles or small spheres (for I know
not which they were) of a rather darker tint appeared within some of
the larger globules. Little globules could now be seen in some of the
uppermost cells of the pedicels, and the protoplasmic lining was
slightly separated from the walls of the lower cells. After 2 hrs. 30
m. from the time of first immersion, the large globules within the
glands of the longer hairs were converted into masses of darker brown
granular matter. Hence from what we have seen with Primula sinensis,
there can be little doubt that these masses originally consisted of
living protoplasm.

A drop of a weak infusion of raw meat was placed on a leaf, and after 2
hrs. 30 m. many spheres could be seen within the glands. These spheres,
when looked at again after 30 m., had slightly changed their positions
and forms, and one had separated into two; but the changes were not
quite like those which the protoplasm of Drosera undergoes. These
hairs, moreover, had not been examined before immersion, and there were
similar spheres in some glands which had not been touched by the
infusion.

Erica tetralix.—A few long glandular hairs project from the margins of
the upper surfaces of the leaves. The pedicels are formed of several
rows of cells, and support rather large globular heads, secreting
viscid matter, by which minute insects are occasionally, though rarely,
caught. Some leaves were left for 23 hrs. in a weak infusion of raw
meat and in water, and the hairs were then compared, but they differed
very little or not at all. In both cases the contents of the cells
seemed rather more granular than they were before; but the granules did
not exhibit any movement. Other leaves were left for 23 hrs. in a
solution of one part of carbonate of ammonia to 218 of water, and here
again the granular matter appeared to have increased [page 352] in
amount; but one such mass retained exactly the same form as before
after an interval of 5 hrs., so that it could hardly have consisted of
living protoplasm. These glands seem to have very little or no power of
absorption, certainly much less than those of the foregoing plants.

Mirabilis longiflora.—The stems and both surfaces of the leaves bear
viscid hairs. young plants, from 12 to 18 inches in height in my
greenhouse, caught so many minute Diptera, Coleoptera, and larvæ, that
they were quite dusted with them. The hairs are short, of unequal
lengths, formed of a single row of cells, surmounted by an enlarged
cell which secretes viscid matter. These terminal cells or glands
contain granules and often globules of granular matter. Within a gland
which had caught a small insect, one such mass was observed to undergo
incessant changes of form, with the occasional appearance of vacuoles.
But I do not believe that this protoplasm had been generated by matter
absorbed from the dead insect; for, on comparing several glands which
had and had not caught insects, not a shade of difference could be
perceived between them, and they all contained fine granular matter. A
piece of leaf was immersed for 24 hrs. in a solution of one part of
carbonate of ammonia to 218 of water, but the hairs seemed very little
affected by it, excepting that perhaps the glands were rendered rather
more opaque. In the leaf itself, however, the grains of chlorophyll
near the cut surfaces had run together, or become aggregated. Nor were
the glands on another leaf, after an immersion for 24 hrs. in an
infusion of raw meat, in the least affected; but the protoplasm lining
the cells of the pedicels had shrunk greatly from the walls. This
latter effect may have been due to exosmose, as the infusion was
strong. We may, therefore, conclude that the glands of this plant
either have no power of absorption or that the protoplasm which they
contain is not acted on by a solution of carbonate of ammonia (and this
seems scarcely credible) or by an infusion of meat.

Nicotiana tabacum.—This plant is covered with innumerable hairs of
unequal lengths, which catch many minute insects. The pedicels of the
hairs are divided by transverse partitions, and the secreting glands
are formed of many cells, containing greenish matter with little
globules of some substance. Leaves were left in an infusion of raw meat
and in water for 26 hrs., but presented no difference. Some of these
same leaves were then left for above 2 hrs. in a solution of carbonate
of ammonia, but no effect was produced. I regret that other experiments
were not tried with more care, as M. Schloesing [page 353] has shown*
that tobacco plants supplied with the vapour of carbonate of ammonia
yield on analysis a greater amount of nitrogen than other plants not
thus treated; and, from what we have seen, it is probable that some of
the vapour may be absorbed by the glandular hairs.]

A Summary of the Observations on Glandular Hairs.—From the foregoing
observations, few as they are, we see that the glands of two species of
Saxifraga, of a Primula and Pelargonium, have the power of rapid
absorption; whereas the glands of an Erica, Mirabilis, and Nicotiana,
either have no such power, or the contents of the cells are not
affected by the fluids employed, namely a solution of carbonate of
ammonia and an infusion of raw meat. As the glands of the Mirabilis
contain protoplasm, which did not become aggregated from exposure to
the fluids just named, though the contents of the cells in the blade of
the leaf were greatly affected by carbonate of ammonia, we may infer
that they cannot absorb. We may further infer that the innumerable
insects caught by this plant are of no more service to it than are
those which adhere to the deciduous and sticky scales of the leaf-buds
of the horse-chestnut.

The most interesting case for us is that of the two species of
Saxifraga, as this genus is distantly allied to Drosera. Their glands
absorb matter from an infusion of raw meat, from solutions of the
nitrate and carbonate of ammonia, and apparently from decayed insects.
This was shown by the changed dull purple colour of the protoplasm
within the cells of the glands, by its state of aggregation, and
apparently by its more rapid spontaneous movements.

* ‘Comptes rendus,’ June 15, 1874. A good abstract of this paper is
given in the ‘Gardener’s Chronicle,’ July 11, 1874. [page 354]


The aggregating process spreads from the glands down the pedicels of
the hairs; and we may assume that any matter which is absorbed
ultimately reaches the tissues of the plant. On the other hand, the
process travels up the hairs whenever a surface is cut and exposed to a
solution of the carbonate of ammonia.

The glands on the flower-stalks and leaves of Primula sinensis quickly
absorb a solution of the carbonate of ammonia, and the protoplasm which
they contain becomes aggregated. The process was seen in some cases to
travel from the glands into the upper cells of the pedicels. Exposure
for 10 m. to the vapour of this salt likewise induced aggregation. When
leaves were left from 6 hrs. to 7 hrs. in a strong solution, or were
long exposed to the vapour, the little masses of protoplasm became
disintegrated, brown, and granular, and were apparently killed. An
infusion of raw meat produced no effect on the glands.

The limpid contents of the glands of Pelargonium zonale became cloudy
and granular in from 3 m. to 5 m. when they were immersed in a weak
solution of the carbonate of ammonia; and in the course of 1 hr.
granules appeared in the upper cells of the pedicels. As the aggregated
masses slowly changed their forms, and as they suffered disintegration
when left for a considerable time in a strong solution, there can be
little doubt that they consisted of protoplasm. It is doubtful whether
an infusion of raw meat produced any effect.

The glandular hairs of ordinary plants have generally been considered
by physiologists to serve only as secreting or excreting organs, but we
now know that they have the power, at least in some cases, of absorbing
both a solution and the vapour of ammonia. As rain-water contains a
small percentage of ammonia, and the atmosphere a minute quantity of
the carbonate, this [page 355] power can hardly fail to be beneficial.
Nor can the benefit be quite so insignificant as it might at first be
thought, for a moderately fine plant of Primula sinensis bears the
astonishing number of above two millions and a half of glandular
hairs,* all of which are able to absorb ammonia brought to them by the
rain. It is moreover probable that the glands of some of the above
named plants obtain animal matter from the insects which are
occasionally entangled by the viscid secretion.

CONCLUDING REMARKS ON THE DROSERACEÆ.


The six known genera composing this family have now been described in
relation to our present subject, as far as my means have permitted.
They all capture insects. This is effected by Drosophyllum, Roridula,
and Byblis, solely by the viscid fluid secreted from their glands; by
Drosera, through the same means, together with the movements of the
tentacles; by Dionaea and Aldrovanda, through the closing of the blades
of the leaf. In these two last genera rapid

* My son Francis counted the hairs on a space measured by means of a
micrometer, and found that there were 35,336 on a square inch of the
upper surface of a leaf, and 30,035 on the lower surface; that is, in
about the proportion of 100 on the upper to 85 on the lower surface. On
a square inch of both surfaces there were 65,371 hairs. A moderately
fine plant bearing twelve leaves (the larger ones being a little more
than 2 inches in diameter) was now selected, and the area of all the
leaves, together with their foot-stalks (the flower-stems not being
included), was found by a planimeter to be 39.285 square inches; so
that the area of both surfaces was 78.57 square inches. Thus the plant
(excluding the flower-stems) must have borne the astonishing number of
2,568,099 glandular hairs. The hairs were counted late in the autumn,
and by the following spring (May) the leaves of some other plants of
the same lot were found to be from one-third to one-fourth broader and
longer than they were before; so that no doubt the glandular hairs had
increased in number, and probably now much exceeded three millions.
[page 356]


movement makes up for the loss of viscid secretion. In every case it is
some part of the leaf which moves. In Aldrovanda it appears to be the
basal parts alone which contract and carry with them the broad, thin
margins of the lobes. In Dionaea the whole lobe, with the exception of
the marginal prolongations or spikes, curves inwards, though the chief
seat of movement is near the midrib. In Drosera the chief seat is in
the lower part of the tentacles, which, homologically, may be
considered as prolongations of the leaf; but the whole blade often
curls inwards, converting the leaf into a temporary stomach.

There can hardly be a doubt that all the plants belonging to these six
genera have the power of dissolving animal matter by the aid of their
secretion, which contains an acid, together with a ferment almost
identical in nature with pepsin; and that they afterwards absorb the
matter thus digested. This is certainly the case with Drosera,
Drosophyllum, and Dionaea; almost certainly with Aldrovanda; and, from
analogy, very probable with Roridula and Byblis. We can thus understand
how it is that the three first-named genera are provided with such
small roots, and that Aldrovanda is quite rootless; about the roots of
the two other genera nothing is known. It is, no doubt, a surprising
fact that a whole group of plants (and, as we shall presently see, some
other plants not allied to the Droseraceae) should subsist partly by
digesting animal matter, and partly by decomposing carbonic acid,
instead of exclusively by this latter means, together with the
absorption of matter from the soil by the aid of roots. We have,
however, an equally anomalous case in the animal kingdom; the
rhizocephalous crustaceans do not feed like other animals by their
mouths, for they are destitute of an [page 357] alimentary canal; but
they live by absorbing through root-like processes the juices of the
animals on which they are parasitic.*

Of the six genera, Drosera has been incomparably the most successful in
the battle for life; and a large part of its success may be attributed
to its manner of catching insects. It is a dominant form, for it is
believed to include about 100 species,** which range in the Old World
from the Arctic regions to Southern India, to the Cape of Good Hope,
Madagascar, and Australia; and in the New World from Canada to Tierra
del Fuego. In this respect it presents a marked contrast with the five
other genera, which appear to be failing groups. Dionaea includes only
a single species, which is confined to one district in Carolina. The
three varieties or closely allied species of Aldrovanda, like so many
water-plants, have a wide range from Central Europe to Bengal and
Australia. Drosophyllum includes only one species, limited to Portugal
and Morocco. Roridula and Byblis each have (as I

* Fritz Müller, ‘Facts for Darwin,’ Eng. trans. 1869, p. 139. The
rhizocephalous crustaceans are allied to the cirripedes. It is hardly
possible to imagine a greater difference than that between an animal
with prehensile limbs, a well-constructed mouth and alimentary canal,
and one destitute of all these organs and feeding by absorption through
branching root-like processes. If one rare cirripede, the Anelasma
squalicola, had become extinct, it would have been very difficult to
conjecture how so enormous a change could have been gradually effected.
But, as Fritz Müller remarks, we have in Anelasma an animal in an
almost exactly intermediate condition, for it has root-like processes
embedded in the skin of the shark on which it is parasitic, and its
prehensile cirri and mouth (as described in my monograph on the
Lepadidae, ‘Ray Soc.’ 1851, p. 169) are in a most feeble and almost
rudimentary condition. Dr. R. Kossmann has given a very interesting
discussion on this subject in his ‘Suctoria and Lepadidae,’ 1873. See
also, Dr. Dohrn, ‘Der Ursprung der Wirbelthiere,’ 1875, p. 77.


** Bentham and Hooker, ‘Genera Plantarum.’ Australia is the metropolis
of the genus, forty-one species having been described from this
country, as Prof. Oliver informs me. [page 358]


hear from Prof. Oliver) two species; the former confined to the western
parts of the Cape of Good Hope, and the latter to Australia. It is a
strange fact that Dionaea, which is one of the most beautifully adapted
plants in the vegetable kingdom, should apparently be on the high-road
to extinction. This is all the more strange as the organs of Dionaea
are more highly differentiated than those of Drosera; its filaments
serve exclusively as organs of touch, the lobes for capturing insects,
and the glands, when excited, for secretion as well as for absorption;
whereas with Drosera the glands serve all these purposes, and secrete
without being excited.

By comparing the structure of the leaves, their degree of complication,
and their rudimentary parts in the six genera, we are led to infer that
their common parent form partook of the characters of Drosophyllum,
Roridula, and Byblis. The leaves of this ancient form were almost
certainly linear, perhaps divided, and bore on their upper and lower
surfaces glands which had the power of secreting and absorbing. Some of
these glands were mounted on pedicels, and others were almost sessile;
the latter secreting only when stimulated by the absorption of
nitrogenous matter. In Byblis the glands consist of a single layer of
cells, supported on a unicellular pedicel; in Roridula they have a more
complex structure, and are supported on pedicels formed of several rows
of cells; in Drosophyllum they further include spiral cells, and the
pedicels include a bundle of spiral vessels. But in these three genera
these organs do not possess any power of movement, and there is no
reason to doubt that they are of the nature of hairs or trichomes.
Although in innumerable instances foliar organs move when excited, no
case is known of a trichome having such [page 359] power.* We are thus
led to inquire how the so-called tentacles of Drosera, which are
manifestly of the same general nature as the glandular hairs of the
above three genera, could have acquired the power of moving. Many
botanists maintain that these tentacles consist of prolongations of the
leaf, because they include vascular tissue, but this can no longer be
considered as a trustworthy distinction.** The possession of the power
of movement on excitement would have been safer evidence. But when we
consider the vast number of the tentacles on both surfaces of the
leaves of Drosophyllum, and on the upper surface of the leaves of
Drosera, it seems scarcely possible that each tentacle could have
aboriginally existed as a prolongation of the leaf. Roridula, perhaps,
shows us how we may reconcile these difficulties with respect to the
homological nature of the tentacles. The lateral divisions of the
leaves of this plant terminate in long tentacles; and these include
spiral vessels which extend for only a short distance up them, with no
line of demarcation between what is plainly the prolongation of the
leaf and the pedicel of a glandular hair. Therefore there would be
nothing anomalous or unusual in the basal parts of these tentacles,
which correspond with the marginal ones of Drosera, acquiring the power
of movement; and we know that in Drosera it is only the lower part
which becomes inflected. But in order to understand how in this latter
genus not only the marginal but all the inner tentacles have become
capable of movement, we must further assume, either that through the
principle of correlated development this

* Sachs, ‘Traité de Botanique’ 3rd edit. 1874, p. 1026.


** Dr. Warming ‘Sur la Diffrence entres les Trichomes,’ Copenhague,
1873, p. 6. ‘Extrait des Videnskabelige Meddelelser de la Soc. d’Hist.
nat. de Copenhague,’ Nos. 10-12, 1872. [page 360]


power was transferred to the basal parts of the hairs, or that the
surface of the leaf has been prolonged upwards at numerous points, so
as to unite with the hairs, thus forming the bases of the inner
tentacles.

The above named three genera, namely Drosophyllum, Roridula, and
Byblis, which appear to have retained a primordial condition, still
bear glandular hairs on both surfaces of their leaves; but those on the
lower surface have since disappeared in the more highly developed
genera, with the partial exception of one species, Drosera binata. The
small sessile glands have also disappeared in some of the genera, being
replaced in Roridula by hairs, and in most species of Drosera by
absorbent papillae. Drosera binata, with its linear and bifurcating
leaves, is in an intermediate condition. It still bears some sessile
glands on both surfaces of the leaves, and on the lower surface a few
irregularly placed tentacles, which are incapable of movement. A
further slight change would convert the linear leaves of this latter
species into the oblong leaves of Drosera anglica, and these might
easily pass into orbicular ones with footstalks, like those of Drosera
rotundifolia. The footstalks of this latter species bear multicellular
hairs, which we have good reason to believe represent aborted
tentacles.

The parent form of Dionaea and Aldrovanda seems to have been closely
allied to Drosera, and to have had rounded leaves, supported on
distinct footstalks, and furnished with tentacles all round the
circumference, with other tentacles and sessile glands on the upper
surface. I think so because the marginal spikes of Dionaea apparently
represent the extreme marginal tentacles of Drosera, the six (sometimes
eight) sensitive filaments on the upper surface, as well as the more
numerous ones in Aldrovanda, representing the central [page 361]
tentacles of Drosera, with their glands aborted, but their
sensitiveness retained. Under this point of view we should bear in mind
that the summits of the tentacles of Drosera, close beneath the glands,
are sensitive.

The three most remarkable characters possessed by the several members
of the Droseraceae consist in the leaves of some having the power of
movement when excited, in their glands secreting a fluid which digests
animal matter, and in their absorption of the digested matter. Can any
light be thrown on the steps by which these remarkable powers were
gradually acquired?

As the walls of the cells are necessarily permeable to fluids, in order
to allow the glands to secrete, it is not surprising that they should
readily allow fluids to pass inwards; and this inward passage would
deserve to be called an act of absorption, if the fluids combined with
the contents of the glands. Judging from the evidence above given, the
secreting glands of many other plants can absorb salts of ammonia, of
which they must receive small quantities from the rain. This is the
case with two species of Saxifraga, and the glands of one of them
apparently absorb matter from captured insects, and certainly from an
infusion of raw meat. There is, therefore, nothing anomalous in the
Droseraceae having acquired the power of absorption in a much more
highly developed degree.

It is a far more remarkable problem how the members of this family, and
Pinguicula, and, as Dr. Hooker has recently shown, Nepenthes, could all
have acquired the power of secreting a fluid which dissolves or digests
animal matter. The six genera of the Droseraceae very probably
inherited this power from a common progenitor, but this cannot apply to
[page 362] Pinguicula or Nepenthes, for these plants are not at all
closely related to the Droceraceae. But the difficulty is not nearly so
great as it at first appears. Firstly, the juices of many plants
contain an acid, and, apparently, any acid serves for digestion.
Secondly, as Dr. Hooker has remarked in relation to the present subject
in his address at Belfast (1874), and as Sachs repeatedly insists,* the
embryos of some plants secrete a fluid which dissolves albuminous
substances out of the endosperm; although the endosperm is not actually
united with, only in contact with, the embryo. All plants, moreover,
have the power of dissolving albuminous or proteid substances, such as
protoplasm, chlorophyll, gluten, aleurone, and of carrying them from
one part to other parts of their tissues. This must be effected by a
solvent, probably consisting of a ferment together with an acid.** Now,
in the case of plants which are able to absorb already soluble matter
from captured insects, though not capable of true digestion, the
solvent just referred to, which must be occasionally present in the
glands, would be apt to exude from the glands together with the viscid
secretion, inasmuch as endosmose is accompanied by exosmose. If such
exudation did ever occur, the solvent would act on the animal matter
contained within the captured insects, and this would be an act of true
digestion. As it cannot be doubted that this process would be of high
service to plants

* ‘Traité de Botanique’ 3rd edit. 1874, p. 844. See also for following
facts pp. 64, 76, 828, 831.


** Since this sentence was written, I have received a paper by
Gorup-Besanez (‘Berichte der Deutschen Chem. Gesellschaft,’ Berlin,
1874, p. 1478), who, with the aid of Dr. H. Will, has actually made the
discovery that the seeds of the vetch contain a ferment, which, when
extracted by glycerine, dissolves albuminous substances, such as
fibrin, and converts them into true peptones. [page 363]


growing in very poor soil, it would tend to be perfected through
natural selection. Therefore, any ordinary plant having viscid glands,
which occasionally caught insects, might thus be converted under
favourable circumstances into a species capable of true digestion. It
ceases, therefore, to be any great mystery how several genera of
plants, in no way closely related together, have independently acquired
this same power.

As there exist several plants the glands of which cannot, as far as is
known, digest animal matter, yet can absorb salts of ammonia and animal
fluids, it is probable that this latter power forms the first stage
towards that of digestion. It might, however, happen, under certain
conditions, that a plant, after having acquired the power of digestion,
should degenerate into one capable only of absorbing animal matter in
solution, or in a state of decay, or the final products of decay,
namely the salts of ammonia. It would appear that this has actually
occurred to a partial extent with the leaves of Aldrovanda; the outer
parts of which possess absorbent organs, but no glands fitted for the
secretion of any digestive fluid, these being confined to the inner
parts.

Little light can be thrown on the gradual acquirement of the third
remarkable character possessed by the more highly developed genera of
the Droseraceae, namely the power of movement when excited. It should,
however, be borne in mind that leaves and their homologues, as well as
flower-peduncles, have gained this power, in innumerable instances,
independently of inheritance from any common parent form; for instance,
in tendril-bearers and leaf-climbers (i.e. plants with their leaves,
petioles and flower-peduncles, &c., modified for prehension) belonging
to a large [page 364] number of the most widely distinct orders,—in the
leaves of the many plants which go to sleep at night, or move when
shaken,—and in the irritable stamens and pistils of not a few species.
We may therefore infer that the power of movement can be by some means
readily acquired. Such movements imply irritability or sensitiveness,
but, as Cohn has remarked,* the tissues of the plants thus endowed do
not differ in any uniform manner from those of ordinary plants; it is
therefore probable that all leaves are to a slight degree irritable.
Even if an insect alights on a leaf, a slight molecular change is
probably transmitted to some distance across its tissue, with the sole
difference that no perceptible effect is produced. We have some
evidence in favour of this belief, for we know that a single touch on
the glands of Drosera does not excite inflection; yet it must produce
some effect, for if the glands have been immersed in a solution of
camphor, inflection follows within a shorter time than would have
followed from the effects of camphor alone. So again with Dionaea, the
blades in their ordinary state may be roughly touched without their
closing; yet some effect must be thus caused and transmitted across the
whole leaf, for if the glands have recently absorbed animal matter,
even a delicate touch causes them to close instantly. On the whole we
may conclude that the acquirement of a high degree of sensitiveness and
of the power of movement by certain genera of the Droseraceae presents
no greater difficulty than that presented by the similar but feebler
powers of a multitude of other plants.

* See the abstract of his memoir on the contractile tissues of plants,
in the ‘Annals and Mag. of Nat. Hist.’ 3rd series, vol. xi. p. 188.)
[page 365]


The specialised nature of the sensitiveness possessed by Drosera and
Dionaea, and by certain other plants, well deserves attention. A gland
of Drosera may be forcibly hit once, twice, or even thrice, without any
effect being produced, whilst the continued pressure of an extremely
minute particle excites movement. On the other hand, a particle many
times heavier may be gently laid on one of the filaments of Dionaea
with no effect; but if touched only once by the slow movement of a
delicate hair, the lobes close; and this difference in the nature of
the sensitiveness of these two plants stands in manifest adaptation to
their manner of capturing insects. So does the fact, that when the
central glands of Drosera absorb nitrogenous matter, they transmit a
motor impulse to the exterior tentacles much more quickly than when
they are mechanically irritated; whilst with Dionaea the absorption of
nitrogenous matter causes the lobes to press together with extreme
slowness, whilst a touch excites rapid movement. Somewhat analogous
cases may be observed, as I have shown in another work, with the
tendrils of various plants; some being most excited by contact with
fine fibres, others by contact with bristles, others with a flat or a
creviced surface. The sensitive organs of Drosera and Dionaea are also
specialised, so as not to be uselessly affected by the weight or impact
of drops of rain, or by blasts of air. This may be accounted for by
supposing that these plants and their progenitors have grown accustomed
to the repeated action of rain and wind, so that no molecular change is
thus induced; whilst they have been rendered more sensitive by means of
natural selection to the rarer impact or pressure of solid bodies.
Although the absorption by the glands of Drosera of various fluids
excites move- [page 366] ment, there is a great difference in the
action of allied fluids; for instance, between certain vegetable acids,
and between citrate and phosphate of ammonia. The specialised nature
and perfection of the sensitiveness in these two plants is all the more
astonishing as no one supposes that they possess nerves; and by testing
Drosera with several substances which act powerfully on the nervous
system of animals, it does not appear that they include any diffused
matter analogous to nerve-tissue.

Although the cells of Drosera and Dionaea are quite as sensitive to
certain stimulants as are the tissues which surround the terminations
of the nerves in the higher animals, yet these plants are inferior even
to animals low down in the scale, in not being affected except by
stimulants in contact with their sensitive parts. They would, however,
probably be affected by radiant heat; for warm water excites energetic
movement. When a gland of Drosera, or one of the filaments of Dionaea,
is excited, the motor impulse radiates in all directions, and is not,
as in the case of animals, directed towards special points or organs.
This holds good even in the case of Drosera when some exciting
substance has been placed at two points on the disc, and when the
tentacles all round are inflected with marvellous precision towards the
two points. The rate at which the motor impulse is transmitted, though
rapid in Dionaea, is much slower than in most or all animals. This
fact, as well as that of the motor impulse not being specially directed
to certain points, are both no doubt due to the absence of nerves.
Nevertheless we perhaps see the prefigurement of the formation of
nerves in animals in the transmission of the motor impulse being so
much more rapid down the confined space within the tentacles of Drosera
than [page 367] elsewhere, and somewhat more rapid in a longitudinal
than in a transverse direction across the disc. These plants exhibit
still more plainly their inferiority to animals in the absence of any
reflex action, except in so far as the glands of Drosera, when excited
from a distance, send back some influence which causes the contents of
the cells to become aggregated down to the bases of the tentacles. But
the greatest inferiority of all is the absence of a central organ, able
to receive impressions from all points, to transmit their effects in
any definite direction, to store them up and reproduce them. [page 368]




CHAPTER XVI.
PINGUICULA.


Pinguicula vulgaris—Structure of leaves—Number of insects and other
objects caught— Movement of the margins of the leaves—Uses of this
movement—Secretion, digestion, and absorption—Action of the secretion
on various animal and vegetable substances—The effects of substances
not containing soluble nitrogenous matter on the glands—Pinguicula
grandiflora—Pinguicula lusitanica, catches insects—Movement of the
leaves, secretion and digestion.


Pinguicula vulgaris.—This plant grows in moist places, generally on
mountains. It bears on an average eight, rather thick, oblong, light
green leaves, having scarcely any footstalk. A full-sized leaf is about
1 1/2 inch in length and 3/4 inch in breadth. The young central leaves
are deeply concave, and project upwards; the older ones towards the
outside are flat or convex, and lie close to the ground, forming a
rosette from 3 to 4 inches in diameter. The margins of the leaves are
incurved. Their upper surfaces are thickly covered with two sets of
glandular hairs, differing in the size of the glands and in the length
of their pedicels. The larger glands have a circular outline as seen
from above, and are of moderate thickness; they are divided by
radiating partitions into sixteen cells, containing light-green,
homogeneous fluid. They are supported on elongated, unicellular
pedicels (containing a nucleus with a nucleolus) which rest on slight
prominences. The small glands differ only in being formed of about half
the number of cells, containing much paler fluid, and supported on much
shorter pedicels. Near the midrib, towards the base of the leaf, the
[page 369] pedicels are multicellular, are longer than elsewhere, and
bear smaller glands. All the glands secrete a colourless fluid, which
is so viscid that I have seen a fine thread drawn out to a length of 18
inches; but the fluid in this case was secreted by a gland which had
been excited. The edge of the leaf is translucent, and does not bear
any glands; and here the spiral vessels, proceeding from the midrib,
terminate in cells marked by a spiral line, somewhat like those within
the glands of Drosera.

The roots are short. Three plants were dug up in North Wales on June
20, and carefully washed; each bore five or six unbranched roots, the
longest of which was only 1.2 of an inch. Two rather young plants were
examined on September 28; these had a greater number of roots, namely
eight and eighteen, all under 1 inch in length, and very little
branched.

I was led to investigate the habits of this plant by being told by Mr.
W. Marshall that on the mountains of Cumberland many insects adhere to
the leaves.

[A friend sent me on June 23 thirty-nine leaves from North Wales, which
were selected owing to objects of some kind adhering to them. Of these
leaves, thirty-two had caught 142 insects, or on an average 4.4 per
leaf, minute fragments of insects not being included. Besides the
insects, small leaves belonging to four different kinds of plants,
those of Erica tetralix being much the commonest, and three minute
seedling plants, blown by the wind, adhered to nineteen of the leaves.
One had caught as many as ten leaves of the Erica. Seeds or fruits,
commonly of Carex and one of Juncus, besides bits of moss and other
rubbish, likewise adhered to six of the thirty-nine leaves. The same
friend, on June 27, collected nine plants bearing seventy-four leaves,
and all of these, with the exception of three young leaves, had caught
insects; thirty insects were counted on one leaf, eighteen on a second,
and sixteen on a third. Another friend examined on August 22 some
plants in Donegal, Ireland, and found insects on 70 out of 157 leaves;
fifteen of [page 370] these leaves were sent me, each having caught on
an average 2.4 insects. To nine of them, leaves (mostly of Erica
tetralix) adhered; but they had been specially selected on this latter
account. I may add that early in August my son found leaves of this
same Erica and the fruits of a Carex on the leaves of a Pinguicula in
Switzerland, probably Pinguicula alpina; some insects, but no great
number, also adhered to the leaves of this plant, which had much better
developed roots than those of Pinguicula vulgaris. In Cumberland, Mr.
Marshall, on September 3, carefully examined for me ten plants bearing
eighty leaves; and on sixty-three of these (i.e. on 79 per cent.) he
found insects, 143 in number; so that each leaf had on an average 2.27
insects. A few days later he sent me some plants with sixteen seeds or
fruits adhering to fourteen leaves. There was a seed on three leaves on
the same plant. The sixteen seeds belonged to nine different kinds,
which could not be recognised, excepting one of Ranunculus, and several
belonging to three or four distinct species of Carex. It appears that
fewer insects are caught late in the year than earlier; thus in
Cumberland from twenty to twenty-four insects were observed in the
middle of July on several leaves, whereas in the beginning of September
the average number was only 2.27. Most of the insects, in all the
foregoing cases, were Diptera, but with many minute Hymenoptera,
including some ants, a few small Coleoptera, larvæ, spiders, and even
small moths.]

We thus see that numerous insects and other objects are caught by the
viscid leaves; but we have no right to infer from this fact that the
habit is beneficial to the plant, any more than in the before given
case of the Mirabilis, or of the horse-chestnut. But it will presently
be seen that dead insects and other nitrogenous bodies excite the
glands to increased secretion; and that the secretion then becomes acid
and has the power of digesting animal substances, such as albumen,
fibrin, &c. Moreover, the dissolved nitrogenous matter is absorbed by
the glands, as shown by their limpid contents being aggregated into
slowly moving granular masses of protoplasm. The same results follow
when insects are naturally captured, and as the plant lives in poor
soil and has small roots, there can be no [page 371] doubt that it
profits by its power of digesting and absorbing matter from the prey
which it habitually captures in such large numbers. It will, however,
be convenient first to describe the movements of the leaves.

Movements of the Leaves.—That such thick, large leaves as those of
Pinguicula vulgarisshould have the power of curving inwards when
excited has never even been suspected. It is necessary to select for
experiment leaves with their glands secreting freely, and which have
been prevented from capturing many insects; as old leaves, at least
those growing in a state of nature, have their margins already curled
so much inwards that they exhibit little power of movement, or move
very slowly. I will first give in detail the more important experiments
which were tried, and then make some concluding remarks.

[Experiment 1.—A young and almost upright leaf was selected, with its
two lateral edges equally and very slightly incurved. A row of small
flies was placed along one margin. When looked at next day, after 15
hrs., this margin, but not the other, was found folded inwards, like
the helix of the human ear, to the breadth of 1/10 of an inch, so as to
lie partly over the row of flies (fig. 15). The glands on which the
flies rested, as well as those on the over-lapping margin which had
been brought into contact with the flies, were all secreting copiously.

FIG. 15. (Pinguicula vulgaris.) Outline of leaf with left margin
inflected over a row of small flies.

Experiment 2.—A row of flies was placed on one margin of a rather old
leaf, which lay flat on the ground; and in this case the margin, after
the same interval as before, namely 15 hrs., had only just begun to
curl inwards; but so much secretion had been poured forth that the
spoon-shaped tip of the leaf was filled with it.

Experiment 3.—Fragments of a large fly were placed close to the apex of
a vigorous leaf, as well as along half one margin. [page 372] After 4
hrs. 20 m. there was decided incurvation, which increased a little
during the afternoon, but was in the same state on the following
morning. Near the apex both margins were inwardly curved. I have never
seen a case of the apex itself being in the least curved towards the
base of the leaf. After 48 hrs. (always reckoning from the time when
the flies were placed on the leaf) the margin had everywhere begun to
unfold.

Experiment 4.—A large fragment of a fly was placed on a leaf, in a
medial line, a little beneath the apex. Both lateral margins were
perceptibly incurved in 3 hrs., and after 4 hrs. 20 m. to such a degree
that the fragment was clasped by both margins. After 24 hrs. the two
infolded edges near the apex (for the lower part of the leaf was not at
all affected) were measured and found to be .11 of an inch (2.795 mm.)
apart. The fly was now removed, and a stream of water poured over the
leaf so as to wash the surface; and after 24 hrs. the margins were .25
of an inch (6.349 mm.) apart, so that they were largely unfolded. After
an additional 24 hrs. they were completely unfolded. Another fly was
now put on the same spot to see whether this leaf, on which the first
fly had been left 24 hrs., would move again; after 10 hrs. there was a
trace of incurvation, but this did not increase during the next 24 hrs.
A bit of meat was also placed on the margin of a leaf, which four days
previously had become strongly incurved over a fragment of a fly and
had afterwards re-expanded; but the meat did not cause even a trace of
incurvation. On the contrary, the margin became somewhat reflexed, as
if injured, and so remained for the three following days, as long as it
was observed.

Experiment 5.—A large fragment of a fly was placed halfway between the
apex and base of a leaf and halfway between the midrib and one margin.
A short space of this margin, opposite the fly, showed a trace of
incurvation after 3 hrs., and this became strongly pronounced in 7 hrs.
After 24 hrs. the infolded edge was only .16 of an inch (4.064 mm.)
from the midrib. The margin now began to unfold, though the fly was
left on the leaf; so that by the next morning (i.e. 48 hrs. from the
time when the fly was first put on) the infolded edge had almost
completely recovered its original position, being now .3 of an inch
(7.62 mm.), instead of .16 of an inch, from the midrib. A trace of
flexure was, however, still visible.

Experiment 6.—A young and concave leaf was selected with its margins
slightly and naturally incurved. Two rather large, oblong, rectangular
pieces of roast meat were placed with their ends touching the infolded
edge, and .46 of an inch (11.68 mm.) [page 373] apart from one another.
After 24 hrs. the margin was greatly and equally incurved (see fig. 16)
throughout this space, and for a length of .12 or .13 of an inch (3.048
or 3.302 mm.) above and below each bit; so that the margin had been
affected over a greater length between the two bits, owing to their
conjoint action, than beyond them. The bits of meat were too large to
be clasped by the margin, but they were tilted up, one of them so as to
stand almost vertically. After 48 hrs. the margin was almost unfolded,
and the bits had sunk down. When again examined after two days, the
margin was quite unfolded, with the exception of the naturally
inflected edge; and one of the bits of meat, the end of which had at
first touched the edge, was now .067 of an inch (1.70 mm.) distant from
it; so that this bit had been pushed thus far across the blade of the
leaf.

FIG. 16. (Pinguicula vulgaris.) Outline of leaf, with right margin
inflected against two square bits of meat.

Experiment 7.—A bit of meat was placed close to the incurved edge of a
rather young leaf, and after it had re-expanded, the bit was left lying
.11 of an inch (2.795 mm.) from the edge. The distance from the edge to
the midrib of the fully expanded leaf was .35 of an inch (8.89 mm.); so
that the bit had been pushed inwards and across nearly one-third of its
semi-diameter.

Experiment 8.—Cubes of sponge, soaked in a strong infusion of raw meat,
were placed in close contact with the incurved edges of two leaves,—an
older and younger one. The distance from the edges to the midribs was
carefully measured. After 1 hr. 17 m. there appeared to be a trace of
incurvation. After 2 hrs. 17 m. both leaves were plainly inflected; the
distance between the edges and midribs being now only half what it was
at first. The incurvation increased slightly during the next 4 1/2
hrs., but remained nearly the same for the next 17 hrs. 30 m. In 35
hrs. from the time when the sponges were placed on the leaves, the
margins were a little unfolded—to a greater degree in the younger than
in the older leaf. The latter was not quite unfolded until the third
day, and now both bits of sponge were left at the distance of .1 of an
inch (2.54 mm.) from the edges; or about a quarter of the distance
between the edge and midrib. A third bit of sponge adhered to the edge,
and, as the margin unfolded, was dragged backwards, into its original
position. [page 374]

Experiment 9.—A chain of fibres of roast meat, as thin as bristles and
moistened with saliva, were placed down one whole side, close to the
narrow, naturally incurved edge of a leaf. In 3 hrs. this side was
greatly incurved along its whole length, and after 8 hrs. formed a
cylinder, about 1/20 of an inch (1.27 mm) in diameter, quite concealing
the meat. This cylinder remained closed for 32 hrs., but after 48 hrs.
was half unfolded, and in 72 hrs. was as open as the opposite margin
where no meat had been placed. As the thin fibres of meat were
completely overlapped by the margin, they were not pushed at all
inwards, across the blade.

Experiment 10.—Six cabbage seeds, soaked for a night in water, were
placed in a row close to the narrow incurved edge of a leaf. We shall
hereafter see that these seeds yield soluble matter to the glands. In 2
hrs. 25 m. the margin was decidedly inflected; in 4 hrs. it extended
over the seeds for about half their breadth, and in 7 hrs. over
three-fourths of their breadth, forming a cylinder not quite closed
along the inner side, and about .7 of an inch (1.778 mm.) in diameter.
After 24 hrs. the inflection had not increased, perhaps had decreased.
The glands which had been brought into contact with the upper surfaces
of the seeds were now secreting freely. In 36 hrs. from the time when
the seeds were put on the leaf the margin had greatly, and after 48
hrs. had completely, re-expanded. As the seeds were no longer held by
the inflected margin, and as the secretion was beginning to fail, they
rolled some way down the marginal channel.

Experiment 11.—Fragments of glass were placed on the margins of two
fine young leaves. After 2 hrs. 30 m. the margin of one certainly
became slightly incurved; but the inflection never increased, and
disappeared in 16 hrs. 30 m. from the time when the fragments were
first applied. With the second leaf there was a trace of incurvation in
2 hrs. 15 m., which became decided in 4 hrs. 30 m., and still more
strongly pronounced in 7 hrs., but after 19 hrs. 30 m. had plainly
decreased. The fragments excited at most a slight and doubtful increase
of the secretion; and in two other trials, no increase could be
perceived. Bits of coal-cinders, placed on a leaf, produced no effect,
either owing to their lightness or to the leaf being torpid.

Experiment 12.—We now turn to fluids. A row of drops of a strong
infusion of raw meat were placed along the margins of two leaves;
squares of sponge soaked in the same infusion being placed on the
opposite margins. My object was to ascer- [page 375] tain whether a
fluid would act as energetically as a substance yielding the same
soluble matter to the glands. No distinct difference was perceptible;
certainly none in the degree of incurvation; but the incurvation round
the bits of sponge lasted rather longer, as might perhaps have been
expected from the sponge remaining damp and supplying nitrogenous
matter for a longer time. The margins, with the drops, became plainly
incurved in 2 hrs. 17 m. The incurvation subsequently increased
somewhat, but after 24 hrs. had greatly decreased.

Experiment 13.—Drops of the same strong infusion of raw meat were
placed along the midrib of a young and rather deeply concave leaf. The
distance across the broadest part of the leaf, between the naturally
incurved edges, was .55 of an inch (13.97 mm.). In 3 hrs. 27 m. this
distance was a trace less; in 6 hrs. 27 m. it was exactly .45 of an
inch (11.43 mm.), and had therefore decreased by .1 of an inch (2.54
mm.). After only 10 hrs. 37 m. the margin began to re-expand, for the
distance from edge to edge was now a trace wider, and after 24 hrs. 20
m. was as great, within a hair’s breadth, as when the drops were first
placed on the leaf. From this experiment we learn that the motor
impulse can be transmitted to a distance of .22 of an inch (5.590 mm.)
in a transverse direction from the midrib to both margins; but it would
be safer to say .2 of an inch (5.08 mm.) as the drops spread a little
beyond the midrib. The incurvation thus caused lasted for an unusually
short time.

Experiment 14.—Three drops of a solution of one part of carbonate of
ammonia to 218 of water (2 grs. to 1 oz.) were placed on the margin of
a leaf. These excited so much secretion that in 1 h. 22 m. all three
drops ran together; but although the leaf was observed for 24 hrs.,
there was no trace of inflection. We know that a rather strong solution
of this salt, though it does not injure the leaves of Drosera,
paralyses their power of movement, and I have no doubt, from the
following case, that this holds good with Pinguicula.

Experiment 15.—A row of drops of a solution of one part of carbonate of
ammonia to 875 of water (1 gr. to 2 oz.) was placed on the margin of a
leaf. In 1 hr. there was apparently some slight incurvation, and this
was well-marked in 3 hrs. 30 m. After 24 hrs. the margin was almost
completely re-expanded.

Experiment 16.—A row of large drops of a solution of one part of
phosphate of ammonia to 4375 of water (1 gr. to 10 oz.) was placed
along the margin of a leaf. No effect was produced, and after 8 hrs.
fresh drops were added along the same margin without the least effect.
We know that a solution of this [page 376] strength acts powerfully on
Drosera, and it is just possible that the solution was too strong. I
regret that I did not try a weaker solution.

Experiment 17.—As the pressure from bits of glass causes incurvation, I
scratched the margins of two leaves for some minutes with a blunt
needle, but no effect was produced. The surface of a leaf beneath a
drop of a strong infusion of raw meat was also rubbed for 10. m. with
the end of a bristle, so as to imitate the struggles of a captured
insect; but this part of the margin did not bend sooner than the other
parts with undisturbed drops of the infusion.]

We learn from the foregoing experiments that the margins of the leaves
curl inwards when excited by the mere pressure of objects not yielding
any soluble matter, by objects yielding such matter, and by some
fluids—namely an infusion of raw meat and a week solution of carbonate
of ammonia. A stronger solution of two grains of this salt to an ounce
of water, though exciting copious secretion, paralyses the leaf. Drops
of water and of a solution of sugar or gum did not cause any movement.
Scratching the surface of the leaf for some minutes produced no effect.
Therefore, as far as we at present know, only two causes—namely slight
continued pressure and the absorption of nitrogenous matter—excite
movement. It is only the margins of the leaf which bend, for the apex
never curves towards the base. The pedicels of the glandular hairs have
no power of movement. I observed on several occasions that the surface
of the leaf became slightly concave where bits of meat or large flies
had long lain, but this may have been due to injury from
over-stimulation.

The shortest time in which plainly marked movement was observed was 2
hrs. 17 m., and this occurred when either nitrogenous substances or
fluids were placed on the leaves; but I believe that in some cases
[page 377] there was a trace of movement in 1 hr. or 1 hr. 30 m. The
pressure from fragments of glass excites movement almost as quickly as
the absorption of nitrogenous matter, but the degree of incurvation
thus caused is much less. After a leaf has become well incurved and has
again expanded, it will not soon answer to a fresh stimulus. The margin
was affected longitudinally, upwards or downwards, for a distance of
.13 of an inch (3.302 mm.) from an excited point, but for a distance of
.46 of an inch between two excited points, and transversely for a
distance of .2 of an inch (5.08 mm.). The motor impulse is not
accompanied, as in the case of Drosera, by any influence causing
increased secretion; for when a single gland was strongly stimulated
and secreted copiously, the surrounding glands were not in the least
affected. The incurvation of the margin is independent of increased
secretion, for fragments of glass cause little or no secretion, and yet
excite movement; whereas a strong solution of carbonate of ammonia
quickly excites copious secretion, but no movement.

One of the most curious facts with respect to the movement of the
leaves is the short time during which they remain incurved, although
the exciting object is left on them. In the majority of cases there was
well-marked re-expansion within 24 hrs. from the time when even large
pieces of meat, &c., were placed on the leaves, and in all cases within
48 hrs. In one instance the margin of a leaf remained for 32 hrs.
closely inflected round thin fibres of meat; in another instance, when
a bit of sponge, soaked in a strong infusion of raw meat, had been
applied to a leaf, the margin began to unfold in 35 hrs. Fragments of
glass keep the margin incurved for a shorter time than do nitrogenous
bodies; for in the former case there was [page 378] complete
re-expansion in 16 hrs. 30 m. Nitrogenous fluids act for a shorter time
than nitrogenous substances; thus, when drops of an infusion of raw
meat were placed on the midrib of a leaf, the incurved margins began to
unfold in only 10 hrs. 37 m., and this was the quickest act of
re-expansion observed by me; but it may have been partly due to the
distance of the margins from the midrib where the drops lay.

We are naturally led to inquire what is the use of this movement which
lasts for so short a time? If very small objects, such as fibres of
meat, or moderately small objects, such as little flies or
cabbage-seeds, are placed close to the margin, they are either
completely or partially embraced by it. The glands of the overlapping
margin are thus brought into contact with such objects and pour forth
their secretion, afterwards absorbing the digested matter. But as the
incurvation lasts for so short a time, any such benefit can be of only
slight importance, yet perhaps greater than at first appears. The plant
lives in humid districts, and the insects which adhere to all parts of
the leaf are washed by every heavy shower of rain into the narrow
channel formed by the naturally incurved edges. For instance, my friend
in North Wales placed several insects on some leaves, and two days
afterwards (there having been heavy rain in the interval) found some of
them quite washed away, and many others safely tucked under the now
closely inflected margins, the glands of which all round the insects
were no doubt secreting. We can thus, also, understand how it is that
so many insects, and fragments of insects, are generally found lying
within the incurved margins of the leaves.

The incurvation of the margin, due to the presence of an exciting
object, must be serviceable in another [page 379] and probably more
important way. We have seen that when large bits of meat, or of sponge
soaked in the juice of meat, were placed on a leaf, the margin was not
able to embrace them, but, as it became incurved, pushed them very
slowly towards the middle of the leaf, to a distance from the outside
of fully .1 of an inch (2.54 mm.), that is, across between one-third
and one-fourth of the space between the edge and midrib. Any object,
such as a moderately sized insect, would thus be brought slowly into
contact with a far larger number of glands, inducing much more
secretion and absorption, than would otherwise have been the case. That
this would be highly serviceable to the plant, we may infer from the
fact that Drosera has acquired highly developed powers of movement,
merely for the sake of bringing all its glands into contact with
captured insects. So again, after a leaf of Dionaea has caught an
insect, the slow pressing together of the two lobes serves merely to
bring the glands on both sides into contact with it, causing also the
secretion charged with animal matter to spread by capillary attraction
over the whole surface. In the case of Pinguicula, as soon as an insect
has been pushed for some little distance towards the midrib, immediate
re-expansion would be beneficial, as the margins could not capture
fresh prey until they were unfolded. The service rendered by this
pushing action, as well as that from the marginal glands being brought
into contact for a short time with the upper surfaces of minute
captured insects, may perhaps account for the peculiar movements of the
leaves; otherwise, we must look at these movements as a remnant of a
more highly developed power formerly possessed by the progenitors of
the genus.

In the four British species, and, as I hear from [page 380] Prof. Dyer,
in most or all the species of the genus, the edges of the leaves are in
some degree naturally and permanently incurved. This incurvation
serves, as already shown, to prevent insects from being washed away by
the rain; but it likewise serves for another end. When a number of
glands have been powerfully excited by bits of meat, insects, or any
other stimulus, the secretion often trickles down the leaf, and is
caught by the incurved edges, instead of rolling off and being lost. As
it runs down the channel, fresh glands are able to absorb the animal
matter held in solution. Moreover, the secretion often collects in
little pools within the channel, or in the spoon-like tips of the
leaves; and I ascertained that bits of albumen, fibrin, and gluten, are
here dissolved more quickly and completely than on the surface of the
leaf, where the secretion cannot accumulate; and so it would be with
naturally caught insects. The secretion was repeatedly seen thus to
collect on the leaves of plants protected from the rain; and with
exposed plants there would be still greater need of some provision to
prevent, as far as possible, the secretion, with its dissolved animal
matter, being wholly lost.

It has already been remarked that plants growing in a state of nature
have the margins of their leaves much more strongly incurved than those
grown in pots and prevented from catching many insects. We have seen
that insects washed down by the rain from all parts of the leaf often
lodge within the margins, which are thus excited to curl farther
inwards; and we may suspect that this action, many times repeated
during the life of the plant, leads to their permanent and well-marked
incurvation. I regret that this view did not occur to me in time to
test its truth.

It may here be added, though not immediately [page 381] bearing on our
subject, that when a plant is pulled up, the leaves immediately curl
downwards so as almost to conceal the roots,—a fact which has been
noticed by many persons. I suppose that this is due to the same
tendency which causes the outer and older leaves to lie flat on the
ground. It further appears that the flower-stalks are to a certain
extent irritable, for Dr. Johnson states that they “bend backwards if
rudely handled.”*

Secretion, Absorption, and Digestion.—I will first give my observations
and experiments, and then a summary of the results.

[The Effects of Objects containing Soluble Nitrogenous Matter.

(1) Flies were placed on many leaves, and excited the glands to secrete
copiously; the secretion always becoming acid, though not so before.
After a time these insects were rendered so tender that their limbs and
bodies could be separated by a mere touch, owing no doubt to the
digestion and disintegration of their muscles. The glands in contact
with a small fly continued to secrete for four days, and then became
almost dry. A narrow strip of this leaf was cut off, and the glands of
the longer and shorter hairs, which had lain in contact for the four
days with the fly, and those which had not touched it, were compared
under the microscope and presented a wonderful contrast. Those which
had been in contact were filled with brownish granular matter, the
others with homogeneous fluid. There could therefore be no doubt that
the former had absorbed matter from the fly.

(2) Small bits of roast meat, placed on a leaf, always caused much acid
secretion in the course of a few hours—in one case within 40 m. When
thin fibres of meat were laid along the margin of a leaf which stood
almost upright, the secretion ran down to the ground. Angular bits of
meat, placed in little pools of the secretion near the margin, were in
the course of

* ‘English Botany,’ by Sir J.E. Smith; with coloured figures by J.
Sowerby; edit. of 1832, tab. 24, 25, 26. [page 382]


two or three days much reduced in size, rounded, rendered more or less
colourless and transparent, and so much softened that they fell to
pieces on the slightest touch. In only one instance was a very minute
particle completely dissolved, and this occurred within 48 hrs. When
only a small amount of secretion was excited, this was generally
absorbed in from 24 hrs. to 48 hrs.; the glands being left dry. But
when the supply of secretion was copious, round either a single rather
large bit of meat, or round several small bits, the glands did not
become dry until six or seven days had elapsed. The most rapid case of
absorption observed by me was when a small drop of an infusion of raw
meat was placed on a leaf, for the glands here became almost dry in 3
hrs. 20 m. Glands excited by small particles of meat, and which have
quickly absorbed their own secretion, begin to secrete again in the
course of seven or eight days from the time when the meat was given
them.

(3) Three minute cubes of tough cartilage from the leg-bone of a sheep
were laid on a leaf. After 10 hrs. 30 m. some acid secretion was
excited, but the cartilage appeared little or not at all affected.
After 24 hrs. the cubes were rounded and much reduced in size; after 32
hrs. they were softened to the centre, and one was quite liquefied;
after 35 hrs. mere traces of solid cartilage were left; and after 48
hrs. a trace could still be seen through a lens in only one of the
three. After 82 hrs. not only were all three cubes completely
liquefied, but all the secretion was absorbed and the glands left dry.

(4) Small cubes of albumen were placed on a leaf; in 8 hrs. feebly acid
secretion extended to a distance of nearly 1/10 of an inch round them,
and the angles of one cube were rounded. After 24 hrs. the angles of
all the cubes were rounded, and they were rendered throughout very
tender; after 30 hrs. the secretion began to decrease, and after 48
hrs. the glands were left dry; but very minute bits of albumen were
still left undissolved.

(5) Smaller cubes of albumen (about 1/50 or 1/60 of an inch, .508 or
.423 mm.) were placed on four glands; after 18 hrs. one cube was
completely dissolved, the others being much reduced in size, softened,
and transparent. After 24 hrs. two of the cubes were completely
dissolved, and already the secretion on these glands was almost wholly
absorbed. After 42 hrs. the two other cubes were completely dissolved.
These four glands began to secrete again after eight or nine days.

(6) Two large cubes of albumen (fully 1/20 of an inch, 1.27 mm.) were
placed, one near the midrib and the other near the margin [page 383] of
a leaf; in 6 hrs. there was much secretion, which after 48 hrs.
accumulated in a little pool round the cube near the margin. This cube
was much more dissolved than that on the blade of the leaf; so that
after three days it was greatly reduced in size, with all the angles
rounded, but it was too large to be wholly dissolved. The secretion was
partially absorbed after four days. The cube on the blade was much less
reduced, and the glands on which it rested began to dry after only two
days.

(7) Fibrin excites less secretion than does meat or albumen. Several
trials were made, but I will give only three of them. Two minute shreds
were placed on some glands, and in 3 hrs. 45 m. their secretion was
plainly increased. The smaller shred of the two was completely
liquefied in 6 hrs. 15 m., and the other in 24 hrs.; but even after 48
hrs. a few granules of fibrin could still be seen through a lens
floating in both drops of secretion. After 56 hrs. 30 m. these granules
were completely dissolved. A third shred was placed in a little pool of
secretion, within the margin of a leaf where a seed had been lying, and
this was completely dissolved in the course of 15 hrs. 30 m.

(8) Five very small bits of gluten were placed on a leaf, and they
excited so much secretion that one of the bits glided down into the
marginal furrow. After a day all five bits seemed much reduced in size,
but none were wholly dissolved. On the third day I pushed two of them,
which had begun to dry, on to fresh glands. On the fourth day
undissolved traces of three out of the five bits could still be
detected, the other two having quite disappeared; but I am doubtful
whether they had really been completely dissolved. Two fresh bits were
now placed, one near the middle and the other near the margin of
another leaf; both excited an extraordinary amount of secretion; that
near the margin had a little pool formed round it, and was much more
reduced in size than that on the blade, but after four days was not
completely dissolved. Gluten, therefore, excites the glands greatly,
but is dissolved with much difficulty, exactly as in the case of
Drosera. I regret that I did not try this substance after having been
immersed in weak hydrochloric acid, as it would then probably have been
quickly dissolved.

(9) A small square thin piece of pure gelatine, moistened with water,
was placed on a leaf, and excited very little secretion in 5 hrs. 30
m., but later in the day a greater amount. After 24 hrs. the whole
square was completely liquefied; and this would not have occurred had
it been left in water. The liquid was acid.

(10) Small particles of chemically prepared casein excited [page 384]
acid secretion, but were not quite dissolved after two days; and the
glands then began to dry. Nor could their complete dissolution have
been expected from what we have seen with Drosera.

(11) Minute drops of skimmed milk were placed on a leaf, and these
caused the glands to secrete freely. After 3 hrs. the milk was found
curdled, and after 23 hrs. the curds were dissolved. On placing the now
clear drops under the microscope, nothing could be detected except some
oil-globules. The secretion, therefore, dissolves fresh casein.

(12) Two fragments of a leaf were immersed for 17 hrs., each in a
drachm of a solution of carbonate of ammonia, of two strengths, namely
of one part to 437 and 218 of water. The glands of the longer and
shorter hairs were then examined, and their contents found aggregated
into granular matter of a brownish-green colour. These granular masses
were seen by my son slowly to change their forms, and no doubt
consisted of protoplasm. The aggregation was more strongly pronounced,
and the movements of the protoplasm more rapid, within the glands
subjected to the stronger solution than in the others. The experiment
was repeated with the same result; and on this occasion I observed that
the protoplasm had shrunk a little from the walls of the single
elongated cells forming the pedicels. In order to observe the process
of aggregation, a narrow strip of leaf was laid edgeways under the
microscope, and the glands were seen to be quite transparent; a little
of the stronger solution (viz. one part to 218 of water) was now added
under the covering glass; after an hour or two the glands contained
very fine granular matter, which slowly became coarsely granular and
slightly opaque; but even after 5 hrs. not as yet of a brownish tint.
By this time a few rather large, transparent, globular masses appeared
within the upper ends of the pedicels, and the protoplasm lining their
walls had shrunk a little. It is thus evident that the glands of
Pinguicula absorb carbonate of ammonia; but they do not absorb it, or
are not acted on by it, nearly so quickly as those of Drosera.

(13) Little masses of the orange-coloured pollen of the common pea,
placed on several leaves, excited the glands to secrete freely. Even a
very few grains which accidentally fell on a single gland caused the
drop surrounding it to increase so much in size, in 23 hrs., as to be
manifestly larger than the drops on the adjoining glands. Grains
subjected to the secretion for 48 hrs. did not emit their tubes; they
were quite discoloured, and seemed to contain less matter than before;
that [page 385] which was left being of a dirty colour, including
globules of oil. They thus differed in appearance from other grains
kept in water for the same length of time. The glands in contact with
the pollen-grains had evidently absorbed matter from them; for they had
lost their natural pale-green tint, and contained aggregated globular
masses of protoplasm.

(14) Square bits of the leaves of spinach, cabbage, and a saxifrage,
and the entire leaves of Erica tetralix, all excited the glands to
increased secretion. The spinach was the most effective, for it caused
the secretion evidently to increase in 1 hr. 40 m., and ultimately to
run some way down the leaf; but the glands soon began to dry, viz.
after 35 hrs. The leaves of Erica tetralix began to act in 7 hrs. 30
m., but never caused much secretion; nor did the bits of leaf of the
saxifrage, though in this case the glands continued to secrete for
seven days. Some leaves of Pinguicula were sent me from North Wales, to
which leaves of Erica tetralixand of an unknown plant adhered; and the
glands in contact with them had their contents plainly aggregated, as
if they had been in contact with insects; whilst the other glands on
the same leaves contained only clear homogeneous fluid.

(15) Seeds.—A considerable number of seeds or fruits selected by
hazard, some fresh and some a year old, some soaked for a short time in
water and some not soaked, were tried. The ten following kinds, namely
cabbage, radish, Anemone nemorosa, Rumex acetosa, Carex sylvatica,
mustard, turnip, cress, Ranunculus acris, and Avena pubescens, all
excited much secretion, which was in several cases tested and found
always acid. The five first-named seeds excited the glands more than
the others. The secretion was seldom copious until about 24 hrs. had
elapsed, no doubt owing to the coats of the seeds not being easily
permeable. Nevertheless, cabbage seeds excited some secretion in 4 hrs.
30 m.; and this increased so much in 18 hrs. as to run down the leaves.
The seeds or properly the fruits of Carex are much oftener found
adhering to leaves in a state of nature than those of any other genus;
and the fruits of Carex sylvatica excited so much secretion that in 15
hrs. it ran into the incurved edges; but the glands ceased to secrete
after 40 hrs. On the other hand, the glands on which the seeds of the
Rumex and Avena rested continued to secrete for nine days.

The nine following kinds of seeds excited only a slight amount of
secretion, namely, celery, parsnip, caraway, Linum grandiflorum,
Cassia, Trifolium pannonicum, Plantago, onion, [page 386] and Bromus.
Most of these seeds did not excite any secretion until 48 hrs. had
elapsed, and in the case of the Trifolium only one seed acted, and this
not until the third day. Although the seeds of the Plantago excited
very little secretion, the glands continued to secrete for six days.
Lastly, the five following kinds excited no secretion, though left on
the leaves for two or three days, namely lettuce, Erica tetralix,
Atriplex hortensis, Phalaris canariensis, and wheat. Nevertheless, when
the seeds of the lettuce, wheat, and Atriplex were split open and
applied to leaves, secretion was excited in considerable quantity in 10
hrs., and I believe that some was excited in six hours. In the case of
the Atriplex the secretion ran down to the margin, and after 24 hrs. I
speak of it in my notes “as immense in quantity and acid.” The split
seeds also of the Trifolium and celery acted powerfully and quickly,
though the whole seeds caused, as we have seen, very little secretion,
and only after a long interval of time. A slice of the common pea,
which however was not tried whole, caused secretion in 2 hrs. From
these facts we may conclude that the great difference in the degree and
rate at which various kinds of seeds excite secretion, is chiefly or
wholly due to the different permeability of their coats.

Some thin slices of the common pea, which had been previously soaked
for 1 hr. in water, were placed on a leaf, and quickly excited much
acid secretion. After 24 hrs. these slices were compared under a high
power with others left in water for the same time; the latter contained
so many fine granules of legumin that the slide was rendered muddy;
whereas the slices which had been subjected to the secretion were much
cleaner and more transparent, the granules of legumin apparently having
been dissolved. A cabbage seed which had lain for two days on a leaf
and had excited much acid secretion, was cut into slices, and these
were compared with those of a seed which had been left for the same
time in water. Those subjected to the secretion were of a paler colour;
their coats presenting the greatest differences, for they were of a
pale dirty tint instead of chestnut-brown. The glands on which the
cabbage seeds had rested, as well as those bathed by the surrounding
secretion, differed greatly in appearance from the other glands on the
same leaf, for they all contained brownish granular matter, proving
that they had absorbed matter from the seeds.

That the secretion acts on the seeds was also shown by some of them
being killed, or by the seedlings being injured. Fourteen cabbage seeds
were left for three days on leaves and excited [page 387] much
secretion; they were then placed on damp sand under conditions known to
be favourable for germination. Three never germinated, and this was a
far larger proportion of deaths than occurred with seeds of the same
lot, which had not been subjected to the secretion, but were otherwise
treated in the same manner. Of the eleven seedlings raised, three had
the edges of their cotyledons slightly browned, as if scorched; and the
cotyledons of one grew into a curious indented shape. Two mustard seeds
germinated; but their cotyledons were marked with brown patches and
their radicles deformed. Of two radish seeds, neither germinated;
whereas of many seeds of the same lot not subjected to the secretion,
all, excepting one, germinated. Of the two Rumex seeds, one died and
the other germinated; but its radicle was brown and soon withered. Both
seeds of the Avena germinated, one grew well, the other had its radicle
brown and withered. Of six seeds of the Erica none germinated, and when
cut open after having been left for five months on damp sand, one alone
seemed alive. Twenty-two seeds of various kinds were found adhering to
the leaves of plants growing in a state of nature; and of these, though
kept for five months on damp sand, none germinated, some being then
evidently dead.

The Effects of Objects not containing Soluble Nitrogenous Matter.

(16) It has already been shown that bits of glass, placed on leaves,
excite little or no secretion. The small amount which lay beneath the
fragments was tested and found not acid. A bit of wood excited no
secretion; nor did the several kinds of seeds of which the coats are
not permeable to the secretion, and which, therefore, acted like
inorganic bodies. Cubes of fat, left for two days on a leaf, produced
no effect.

(17) A particle of white sugar, placed on a leaf, formed in 1 hr. 10 m.
a large drop of fluid, which in the course of 2 additional hours ran
down into the naturally inflected margin. This fluid was not in the
least acid, and began to dry up, or more probably was absorbed, in 5
hrs. 30 m. The experiment was repeated; particles being placed on a
leaf, and others of the same size on a slip of glass in a moistened
state; both being covered by a bell-glass. This was done to see whether
the increased amount of fluid on the leaves could be due to mere
deliquescence; but this was proved not to be the case. The particle on
the leaf caused so much secretion that in the course of 4 hrs. it ran
down across two-thirds of the leaf. After 8 hrs. the leaf, which was
concave, was actually filled with very viscid [page 388] fluid; and it
particularly deserves notice that this, as on the former occasion, was
not in the least acid. This great amount of secretion may be attributed
to exosmose. The glands which had been covered for 24 hrs. by this
fluid did not differ, when examined under the microscope, from others
on the same leaf, which had not come into contact with it. This is an
interesting fact in contrast with the invariably aggregated condition
of glands which have been bathed by the secretion, when holding animal
matter in solution.

(18) Two particles of gum arabic were placed on a leaf, and they
certainly caused in 1 hr. 20 m. a slight increase of secretion. This
continued to increase for the next 5 hrs., that is for as long a time
as the leaf was observed.

(19) Six small particles of dry starch of commerce were placed on a
leaf, and one of these caused some secretion in 1 hr. 15 m., and the
others in from 8 hrs. to 9 hrs. The glands which had thus been excited
to secrete soon became dry, and did not begin to secrete again until
the sixth day. A larger bit of starch was then placed on a leaf, and no
secretion was excited in 5 hrs. 30 m.; but after 8 hrs. there was a
considerable supply, which increased so much in 24 hrs. as to run down
the leaf to the distance of 3/4 of an inch. This secretion, though so
abundant, was not in the least acid. As it was so copiously excited,
and as seeds not rarely adhere to the leaves of naturally growing
plants, it occurred to me that the glands might perhaps have the power
of secreting a ferment, like ptyaline, capable of dissolving starch; so
I carefully observed the above six small particles during several days,
but they did not seem in the least reduced in bulk. A particle was also
left for two days in a little pool of secretion, which had run down
from a piece of spinach leaf; but although the particle was so minute
no diminution was perceptible. We may therefore conclude that the
secretion cannot dissolve starch. The increase caused by this substance
may, I presume, be attributed to exosmose. But I am surprised that
starch acted so quickly and powerfully as it did, though in a less
degree than sugar. Colloids are known to possess some slight power of
dialysis; and on placing the leaves of a Primula in water, and others
in syrup and diffused starch, those in the starch became flaccid, but
to a less degree and at a much slower rate than the leaves in the
syrup; those in water remaining all the time crisp.]

From the foregoing experiments and observations we [page 389] see that
objects not containing soluble matter have little or no power of
exciting the glands to secrete. Non-nitrogenous fluids, if dense, cause
the glands to pour forth a large supply of viscid fluid, but this is
not in the least acid. On the other hand, the secretion from glands
excited by contact with nitrogenous solids or liquids is invariably
acid, and is so copious that it often runs down the leaves and collects
within the naturally incurved margins. The secretion in this state has
the power of quickly dissolving, that is of digesting, the muscles of
insects, meat, cartilage, albumen, fibrin, gelatine, and casein as it
exists in the curds of milk. The glands are strongly excited by
chemically prepared casein and gluten; but these substances (the latter
not having been soaked in weak hydrochloric acid) are only partially
dissolved, as was likewise the case with Drosera. The secretion, when
containing animal matter in solution, whether derived from solids or
from liquids, such as an infusion of raw meat, milk, or a weak solution
of carbonate of ammonia, is quickly absorbed; and the glands, which
were before limpid and of a greenish colour, become brownish and
contain masses of aggregated granular matter. This matter, from its
spontaneous movements, no doubt consists of protoplasm. No such effect
is produced by the action of non-nitrogenous fluids. After the glands
have been excited to secrete freely, they cease for a time to secrete,
but begin again in the course of a few days.

Glands in contact with pollen, the leaves of other plants, and various
kinds of seeds, pour forth much acid secretion, and afterwards absorb
matter probably of an albuminous nature from them. Nor can the benefit
thus derived be insignificant, for a considerable [page 390] amount of
pollen must be blown from the many wind-fertilised carices, grasses,
&c., growing where Pinguicula lives, on to the leaves thickly covered
with viscid glands and forming large rosettes. Even a few grains of
pollen on a single gland causes it to secrete copiously. We have also
seen how frequently the small leaves of Erica tetralix and of other
plants, as well as various kinds of seeds and fruits, especially of
Carex, adhere to the leaves. One leaf of the Pinguicula had caught ten
of the little leaves of the Erica; and three leaves on the same plant
had each caught a seed. Seeds subjected to the action of the secretion
are sometimes killed, or the seedlings injured. We may, therefore,
conclude that Pinguicula vulgaris, with its small roots, is not only
supported to a large extent by the extraordinary number of insects
which it habitually captures, but likewise draws some nourishment from
the pollen, leaves, and seeds of other plants which often adhere to its
leaves. It is therefore partly a vegetable as well as an animal feeder.

PINGUICULA GRANDIFLORA.


This species is so closely allied to the last that it is ranked by Dr.
Hooker as a sub-species. It differs chiefly in the larger size of its
leaves, and in the glandular hairs near the basal part of the midrib
being longer. But it likewise differs in constitution; I hear from Mr.
Ralfs, who was so kind as to send me plants from Cornwall, that it
grows in rather different sites; and Dr. Moore, of the Glasnevin
Botanic Gardens, informs me that it is much more manageable under
culture, growing freely and flowering annually; whilst Pinguicula
vulgaris has to be renewed every year. Mr. Ralfs found numerous [page
391] insects and fragments of insects adhering to almost all the
leaves. These consisted chiefly of Diptera, with some Hymenoptera,
Homoptera, Coleoptera, and a moth. On one leaf there were nine dead
insects, besides a few still alive. He also observed a few fruits of
Carex pulicaris, as well as the seeds of this same Pinguicula, adhering
to the leaves. I tried only two experiments with this species; firstly,
a fly was placed near the margin of a leaf, and after 16 hrs. this was
found well inflected. Secondly, several small flies were placed in a
row along one margin of another leaf, and by the next morning this
whole margin was curled inwards, exactly as in the case of Pinguicula
vulgaris.

PINGUICULA LUSITANICA.


This species, of which living specimens were sent me by Mr. Ralfs from
Cornwall, is very distinct from the two foregoing ones. The leaves are
rather smaller, much more transparent, and are marked with purple
branching veins. The margins of the leaves are much more involuted;
those of the older ones extending over a third of the space between the
midrib and the outside. As in the two other species, the glandular
hairs consist of longer and shorter ones, and have the same structure;
but the glands differ in being purple, and in often containing granular
matter before they have been excited. In the lower part of the leaf,
almost half the space on each side between the midrib and margin is
destitute of glands; these being replaced by long, rather stiff,
multicellular hairs, which intercross over the midrib. These hairs
perhaps serve to prevent insects from settling on this part of the
leaf, where there are no viscid glands by which they could be caught;
but it is hardly probable that they were developed for this purpose.
The spiral vessels pro- [page 392] ceeding from the midrib terminate at
the extreme margin of the leaf in spiral cells; but these are not so
well developed as in the two preceding species. The flower-peduncles,
sepals, and petals, are studded with glandular hairs, like those on the
leaves.

The leaves catch many small insects, which are found chiefly beneath
the involuted margins, probably washed there by the rain. The colour of
the glands on which insects have long lain is changed, being either
brownish or pale purple, with their contents coarsely granular; so that
they evidently absorb matter from their prey. Leaves of the Erica
tetralix, flowers of a Galium, scales of grasses, &c. likewise adhered
to some of the leaves. Several of the experiments which were tried on
Pinguicula vulgaris were repeated on Pinguicula lusitanica, and these
will now be given.

[(1) A moderately sized and angular bit of albumen was placed on one
side of a leaf, halfway between the midrib and the naturally involuted
margin. In 2 hrs. 15 m. the glands poured forth much secretion, and
this side became more infolded than the opposite one. The inflection
increased, and in 3 hrs. 30 m. extended up almost to the apex. After 24
hrs. the margin was rolled into a cylinder, the outer surface of which
touched the blade of the leaf and reached to within the 1/20 of an inch
of the midrib. After 48 hrs. it began to unfold, and in 72 hrs. was
completely unfolded. The cube was rounded and greatly reduced in size;
the remainder being in a semi-liquefied state.

(2) A moderately sized bit of albumen was placed near the apex of a
leaf, under the naturally incurved margin. In 2 hrs. 30 m. much
secretion was excited, and next morning the margin on this side was
more incurved than the opposite one, but not to so great a degree as in
the last case. The margin unfolded at the same rate as before. A large
proportion of the albumen was dissolved, a remnant being still left.

(3) Large bits of albumen were laid in a row on the midribs of two
leaves, but produced in the course of 24 hrs. no effect; [page 393] nor
could this have been expected, for even had glands existed here, the
long bristles would have prevented the albumen from coming in contact
with them. On both leaves the bits were now pushed close to one margin,
and in 3 hrs. 30 m. this became so greatly inflected that the outer
surface touched the blade; the opposite margin not being in the least
affected. After three days the margins of both leaves with the albumen
were still as much inflected as ever, and the glands were still
secreting copiously. With Pinguicula vulgaris I have never seen
inflection lasting so long.

(4) Two cabbage seeds, after being soaked for an hour in water, were
placed near the margin of a leaf, and caused in 3 hrs. 20 m. increased
secretion and incurvation. After 24 hrs. the leaf was partially
unfolded, but the glands were still secreting freely. These began to
dry in 48 hrs., and after 72 hrs. were almost dry. The two seeds were
then placed on damp sand under favourable conditions for growth; but
they never germinated, and after a time were found rotten. They had no
doubt been killed by the secretion.

(5) Small bits of a spinach leaf caused in 1 hr. 20 m. increased
secretion; and after 3 hrs. 20 m. plain incurvation of the margin. The
margin was well inflected after 9 hrs. 15 m., but after 24 hrs. was
almost fully re-expanded. The glands in contact with the spinach became
dry in 72 hrs. Bits of albumen had been placed the day before on the
opposite margin of this same leaf, as well as on that of a leaf with
cabbage seeds, and these margins remained closely inflected for 72
hrs., showing how much more enduring is the effect of albumen than of
spinach leaves or cabbage seeds .

(6) A row of small fragments of glass was laid along one margin of a
leaf; no effect was produced in 2 hrs. 10 m., but after 3 hrs. 25 m.
there seemed to be a trace of inflection, and this was distinct, though
not strongly marked, after 6 hrs. The glands in contact with the
fragments now secreted more freely than before; so that they appear to
be more easily excited by the pressure of inorganic objects than are
the glands of Pinguicula vulgaris. The above slight inflection of the
margin had not increased after 24 hrs., and the glands were now
beginning to dry. The surface of a leaf, near the midrib and towards
the base, was rubbed and scratched for some time, but no movement
ensued. The long hairs which are situated here were treated in the same
manner, with no effect. This latter trial was made because I thought
that the hairs might perhaps be sensitive to a touch, like the
filaments of Dionaea. [page 394]

(7) The flower-peduncles, sepals and petals, bear glands in general
appearance like those on the leaves. A piece of a flower-peduncle was
therefore left for 1 hr. in a solution of one part of carbonate of
ammonia to 437 of water, and this caused the glands to change from
bright pink to a dull purple colour; but their contents exhibited no
distinct aggregation. After 8 hrs. 30 m. they became colourless. Two
minute cubes of albumen were placed on the glands of a flower-peduncle,
and another cube on the glands of a sepal; but they were not excited to
increased secretion, and the albumen after two days was not in the
least softened. Hence these glands apparently differ greatly in
function from those on the leaves.]

From the foregoing observations on Pinguicula lusitanica we see that
the naturally much incurved margins of the leaves are excited to curve
still farther inwards by contact with organic and inorganic bodies;
that albumen, cabbage seeds, bits of spinach leaves, and fragments of
glass, cause the glands to secrete more freely;—that albumen is
dissolved by the secretion, and cabbage seeds killed by it;—and lastly
that matter is absorbed by the glands from the insects which are caught
in large numbers by the viscid secretion. The glands on the
flower-peduncles seem to have no such power. This species differs from
Pinguicula vulgarisand grandiflora in the margins of the leaves, when
excited by organic bodies, being inflected to a greater degree, and in
the inflection lasting for a longer time. The glands, also, seem to be
more easily excited to increased secretion by bodies not yielding
soluble nitrogenous matter. In other respects, as far as my
observations serve, all three species agree in their functional powers.
[page 395]




CHAPTER XVII.
UTRICULARIA.


Utricularia neglecta—Structure of the bladder—The uses of the several
parts—Number of imprisoned animals—Manner of capture—The bladders
cannot digest animal matter, but absorb the products of its
decay—Experiments on the absorption of certain fluids by the quadrifid
processes—Absorption by the glands—Summary of the observation on
absorption— Development of the bladders—Utricularia
vulgaris—Utricularia minor—Utricularia clandestina.


I was led to investigate the habits and structure of the species of
this genus partly from their belonging to the same natural family as
Pinguicula, but more especially by Mr. Holland’s statement, that “water
insects are often found imprisoned in the bladders,” which he suspects
“are destined for the plant to feed on.”* The plants which I first
received as Utricularia vulgaris from the New Forest in Hampshire and
from Cornwall, and which I have chiefly worked on, have been determined
by Dr. Hooker to be a very rare British species, the Utricularia
neglecta of Lehm.** I subsequently received the true Utricularia
vulgaris from Yorkshire. Since drawing up the following description
from my own observations and those of my son, Francis Darwin, an
important memoir by Prof. Cohn

* The ‘Quart. Mag. of the High Wycombe Nat. Hist. Soc.’ July 1868, p.
5. Delpino (‘Ult. Osservaz. sulla Dicogamia,’ &c. 1868-1869, p. 16)
also quotes Crouan as having found (1858) crustaceans within the
bladders of Utricularia vulgaris.


** I am much indebted to the Rev. H.M. Wilkinson, of Bistern, for
having sent me several fine lots of this species from the New Forest.
Mr. Ralfs was also so kind as to send me living plants of the same
species from near Penzance in Cornwall. [page 396]


on Utricularia vulgaris has appeared;* and it has been no small
satisfaction to me to find that my account agrees almost completely
with that of this distinguished observer. I will publish my description
as it stood before reading that by Prof. Cohn, adding occasionally some
statements on his authority.

FIG. 17. (Utricularia neglecta.) Branch with the divided leaves bearing
bladders; about twice enlarged.

Utricularia neglecta.—The general appearance of a branch (about twice
enlarged), with the pinnatifid leaves bearing bladders, is represented
in the above sketch (fig. 17). The leaves continually bifurcate, so
that a full-grown one terminates in from twenty to thirty

* ‘Beitrage zur Biologie der Plflanzen’ drittes Heft, 1875. [page 397]


points. Each point is tipped by a short, straight bristle; and slight
notches on the sides of the leaves bear similar bristles. On both
surfaces there are many small papillae, crowned with two hemispherical
cells in close contact. The plants float near the surface of the water,
and are quite destitute of roots, even during the earliest period of
growth.* They commonly inhabit, as more than one observer has remarked
to me, remarkably foul ditches.

The bladders offer the chief point of interest. There are often two or
three on the same divided leaf, generally near the base; though I have
seen a single one growing from the stem. They are supported on short
footstalks. When fully grown, they are nearly 1/10 of an inch (2.54
mm.) in length. They are translucent, of a green colour, and the walls
are formed of two layers of cells. The exterior cells are polygonal and
rather large; but at many of the points where the angles meet, there
are smaller rounded cells. These latter support short conical
projections, surmounted by two hemispherical cells in such close
apposition that they appear united; but they often separate a little
when immersed in certain fluids. The papillae thus formed are exactly
like those on the surfaces of the leaves. Those on the same bladder
vary much in size; and there are a few, especially on very young
bladders, which have an elliptical instead of a circular outline. The
two terminal cells are transparent, but must hold much matter in
solution, judging from the quantity coagulated by prolonged immersion
in alcohol or ether.

* I infer that this is the case from a drawing of a seedling given by
Dr. Warming in his paper, “Bidrag til Kundskaben om Lentibulariaceae,”
from the ‘Videnskabelige Meddelelser,’ Copenhagen, 1874, Nos. 3-7, pp.
33-58.) [page 398]


The bladders are filled with water. They generally, but by no means
always, contain bubbles of air. According to the quantity of the
contained water and air, they vary much in thickness, but are always
somewhat compressed. At an early stage of growth, the flat or ventral
surface faces the axis or stem; but the footstalks must have some power
of movement; for in plants kept in my greenhouse the ventral surface
was generally turned either straight or obliquely downwards. The Rev.
H.M. Wilkinson examined

FIG. 18. (Utricularia neglecta.) Bladder; much enlarged. c, collar
indistinctly seen through the walls.

plants for me in a state of nature, and found this commonly to be the
case, but the younger bladders often had their valves turned upwards.

The general appearance of a bladder viewed laterally, with the
appendages on the near side alone represented, is shown in the
accompanying figure (fig. 18). The lower side, where the footstalk
arises, is nearly straight, and I have called it the ventral surface.
The other or dorsal surface is convex, and terminates in two long
prolongations, formed of several rows of cells, containing chlorophyll,
and bearing, chiefly on [page 399] the outside, six or seven long,
pointed, multicellular bristles. These prolongations of the bladder may
be conveniently called the antennæ, for the whole bladder (see fig. 17)
curiously resembles an entomostracan crustacean, the short footstalk
representing the tail. In fig. 18, the near antenna alone is shown.
Beneath the two antennæ the end of the bladder is slightly truncated,
and here is situated the most important part of the whole structure,
namely the entrance and valve. On each side of the entrance from three
to rarely seven long, multicellular bristles project out-

FIG. 19. (Utricularia neglecta.) Valve of bladder; greatly enlarged.

wards; but only those (four in number) on the near side are shown in
the drawing. These bristles, together with those borne by the antennæ,
form a sort of hollow cone surrounding the entrance.

The valve slopes into the cavity of the bladder, or upwards in fig. 18.
It is attached on all sides to the bladder, excepting by its posterior
margin, or the lower one in fig. 19, which is free, and forms one side
of the slit-like orifice leading into the bladder. This margin is
sharp, thin, and smooth, and rests on the edge of a rim or collar,
which dips deeply into the [page 400] bladder, as shown in the
longitudinal section (fig. 20) of the collar and valve; it is also
shown at c, in fig. 18. The edge of the valve can thus open only
inwards. As both the valve and collar dip into the bladder, a hollow or
depression is here formed, at the base of which lies the slit-like
orifice.

The valve is colourless, highly transparent, flexible and elastic. It
is convex in a transverse direction, but has been drawn (fig. 19) in a
flattened state, by which its apparent breadth is increased. It is
formed,

FIG. 20. (Utricularia neglecta.) Longitudinal vertical section through
the ventral portion of a bladder; showing valve and collar. v, valve;
the whole projection above c forms the collar; b, bifid processes; s,
ventral surface of bladder.

according to Cohn, of two layers of small cells, which are continuous
with the two layers of larger cells forming the walls of the bladder,
of which it is evidently a prolongation. Two pairs of transparent
pointed bristles, about as long as the valve itself, arise from near
the free posterior margin (fig. 18), and point obliquely outwards in
the direction of the antennæ. There are also on the surface of the
valve numerous glands, as I will call them; for they have the power of
absorption, though I doubt whether they ever secrete. They consist of
three kinds, which [page 401] to a certain extent graduate into one
another. Those situated round the anterior margin of the valve (upper
margin in fig. 19) are very numerous and crowded together; they consist
of an oblong head on a long pedicel. The pedicel itself is formed of an
elongated cell, surmounted by a short one. The glands towards the free
posterior margin are much larger, few in number, and almost spherical,
having short footstalks; the head is formed by the confluence of two
cells, the lower one answering to the short upper cell of the pedicel
of the oblong glands. The glands of the third kind have transversely
elongated heads, and are seated on very short footstalks; so that they
stand parallel and close to the surface of the valve; they may be
called the two-armed glands. The cells forming all these glands contain
a nucleus, and are lined by a thin layer of more or less granular
protoplasm, the primordial utricle of Mohl. They are filled with fluid,
which must hold much matter in solution, judging from the quantity
coagulated after they have been long immersed in alcohol or ether. The
depression in which the valve lies is also lined with innumerable
glands; those at the sides having oblong heads and elongated pedicels,
exactly like the glands on the adjoining parts of the valve.

The collar (called the peristome by Cohn) is evidently formed, like the
valve, by an inward projection of the walls of the bladder. The cells
composing the outer surface, or that facing the valve, have rather
thick walls, are of a brownish colour, minute, very numerous, and
elongated; the lower ones being divided into two by vertical
partitions. The whole presents a complex and elegant appearance. The
cells forming the inner surface are continuous with those over the
whole inner surface of the bladder. The space be- [page 402] tween the
inner and outer surface consists of coarse cellular tissue (fig. 20).
The inner side is thickly covered with delicate bifid processes,
hereafter to be described. The collar is thus made thick; and it is
rigid, so that it retains the same outline whether the bladder contains
little or much air and water. This is of great importance, as otherwise
the thin and flexible valve would be liable to be distorted, and in
this case would not act properly.

Altogether the entrance into the bladder, formed by the transparent
valve, with its four obliquely projecting bristles, its numerous
diversely shaped glands, surrounded by the collar, bearing glands on
the inside and bristles on the outside, together with the bristles
borne by the antennæ, presents an extraordinarily complex appearance
when viewed under the microscope.

We will now consider the internal structure of the bladder. The whole
inner surface, with the exception of the valve, is seen under a
moderately high power to be covered with a serried mass of processes
(fig. 21). Each of these consists of four divergent arms; whence their
name of quadrifid processes. They arise from small angular cells, at
the junctions of the angles of the larger cells which form the interior
of the bladder. The middle part of the upper surface of these small
cells projects a little, and then contracts into a very short and
narrow footstalk which bears the four arms (fig. 22.). Of these, two
are long, but often of not quite equal length, and project obliquely
inwards and towards the posterior end of the bladder. The two others
are much shorter, and project at a smaller angle, that is, are more
nearly horizontal, and are directed towards the anterior end of the
bladder. These arms are only moderately sharp; they are composed of ex-
[page 403] tremely thin transparent membrane, so that they can be bent
or doubled in any direction without being broken. They are lined with a
delicate layer of protoplasm, as is likewise the short conical
projection from which they arise. Each arm generally (but not
invariably) contains a minute, faintly brown particle, either rounded
or more commonly elongated, which exhibits incessant Brownian
movements. These par-

FIG. 21. (Utricularia neglecta.) Small portion of inside of bladder,
much enlarged, showing quadrifid processes.

FIG. 22. (Utricularia neglecta.) One of the quadrifid processes greatly
enlarged.

ticles slowly change their positions, and travel from one end to the
other of the arms, but are commonly found near their bases. They are
present in the quadrifids of young bladders, when only about a third of
their full size. They do not resemble ordinary nuclei, but I believe
that they are nuclei in a modified condition, for when absent, I could
occasionally just distinguish in their places a delicate halo of
matter, including a darker spot. Moreover, the quadrifids of
Utricularia montana contain rather larger and much [page 404] more
regularly spherical, but otherwise similar, particles, which closely
resemble the nuclei in the cells forming the walls of the bladders. In
the present case there were sometimes two, three, or even more, nearly
similar particles within a single arm; but, as we shall hereafter see,
the presence of more than one seemed always to be connected with the
absorption of decayed matter.

The inner side of the collar (see the previous fig. 20) is covered with
several crowded rows of processes, differing in no important respect
from the quadrifids, except in bearing only two arms instead of four;
they are, however, rather narrower and more delicate. I shall call them
the bifids. They project into the bladder, and are directed towards its
posterior end. The quadrifid and bifid processes no doubt are
homologous with the papillae on the outside of the bladder and of the
leaves; and we shall see that they are developed from closely similar
papillae.

The Uses of the several Parts.—After the above long but necessary
description of the parts, we will turn to their uses. The bladders have
been supposed by some authors to serve as floats; but branches which
bore no bladders, and others from which they had been removed, floated
perfectly, owing to the air in the intercellular spaces. Bladders
containing dead and captured animals usually include bubbles of air,
but these cannot have been generated solely by the process of decay, as
I have often seen air in young, clean, and empty bladders; and some old
bladders with much decaying matter had no bubbles.

The real use of the bladders is to capture small aquatic animals, and
this they do on a large scale. In the first lot of plants, which I
received from the New Forest early in July, a large proportion of the
fully [page 405] grown bladders contained prey; in a second lot,
received in the beginning of August, most of the bladders were empty,
but plants had been selected which had grown in unusually pure water.
In the first lot, my son examined seventeen bladders, including prey of
some kind, and eight of these contained entomostracan crustaceans,
three larvæ of insects, one being still alive, and six remnants of
animals so much decayed that their nature could not be distinguished. I
picked out five bladders which seemed very full, and found in them
four, five, eight, and ten crustaceans, and in the fifth a single much
elongated larva. In five other bladders, selected from containing
remains, but not appearing very full, there were one, two, four, two,
and five crustaceans. A plant of Utricularia vulgaris, which had been
kept in almost pure water, was placed by Cohn one evening into water
swarming with crustaceans, and by the next morning most of the bladders
contained these animals entrapped and swimming round and round their
prisons. They remained alive for several days; but at last perished,
asphyxiated, as I suppose, by the oxygen in the water having been all
consumed. Freshwater worms were also found by Cohn in some bladders. In
all cases the bladders with decayed remains swarmed with living Algae
of many kinds, Infusoria, and other low organisms, which evidently
lived as intruders.

Animals enter the bladders by bending inwards the posterior free edge
of the valve, which from being highly elastic shuts again instantly. As
the edge is extremely thin, and fits closely against the edge of the
collar, both projecting into the bladder (see section, fig. 20), it
would evidently be very difficult for any animal to get out when once
imprisoned, and apparently they never do escape. To show how closely
the edge [page 406] fits, I may mention that my son found a Daphnia
which had inserted one of its antennæ into the slit, and it was thus
held fast during a whole day. On three or four occasions I have seen
long narrow larvæ, both dead and alive, wedged between the corner of
the valve and collar, with half their bodies within the bladder and
half out.

As I felt much difficulty in understanding how such minute and weak
animals, as are often captured, could force their way into the
bladders, I tried many experiments to ascertain how this was effected.
The free margin of the valve bends so easily that no resistance is felt
when a needle or thin bristle is inserted. A thin human hair, fixed to
a handle, and cut off so as to project barely 1/4 of an inch, entered
with some difficulty; a longer piece yielded instead of entering. On
three occasions minute particles of blue glass (so as to be easily
distinguished) were placed on valves whilst under water; and on trying
gently to move them with a needle, they disappeared so suddenly that,
not seeing what had happened, I thought that I had flirted them off;
but on examining the bladders, they were found safely enclosed. The
same thing occurred to my son, who placed little cubes of green
box-wood (about 1/60 of an inch, .423 mm.) on some valves; and thrice
in the act of placing them on, or whilst gently moving them to another
spot, the valve suddenly opened and they were engulfed. He then placed
similar bits of wood on other valves, and moved them about for some
time, but they did not enter. Again, particles of blue glass were
placed by me on three valves, and extremely minute shavings of lead on
two other valves; after 1 or 2 hrs. none had entered, but in from 2 to
5 hrs. all five were enclosed. One of the particles of glass was a
[page 407] long splinter, of which one end rested obliquely on the
valve, and after a few hours it was found fixed, half within the
bladder and half projecting out, with the edge of the valve fitting
closely all round, except at one angle, where a small open space was
left. It was so firmly fixed, like the above-mentioned larvæ, that the
bladder was torn from the branch and shaken, and yet the splinter did
not fall out. My son also placed little cubes (about 1/65 of an inch,
.391 mm.) of green box-wood, which were just heavy enough to sink in
water, on three valves. These were examined after 19 hrs. 30 m., and
were still lying on the valves; but after 22 hrs. 30 m. one was found
enclosed. I may here mention that I found in a bladder on a naturally
growing plant a grain of sand, and in another bladder three grains;
these must have fallen by some accident on the valves, and then entered
like the particles of glass.

The slow bending of the valve from the weight of particles of glass and
even of box-wood, though largely supported by the water, is, I suppose,
analogous to the slow bending of colloid substances. For instance,
particles of glass were placed on various points of narrow strips of
moistened gelatine, and these yielded and became bent with extreme
slowness. It is much more difficult to understand how gently moving a
particle from one part of a valve to another causes it suddenly to
open. To ascertain whether the valves were endowed with irritability,
the surfaces of several were scratched with a needle or brushed with a
fine camel-hair brush, so as to imitate the crawling movement of small
crustaceans, but the valve did not open. Some bladders, before being
brushed, were left for a time in water at temperatures between 80° and
130° F. (26°.6-54°.4 Cent.), as, judging from a wide- [page 408] spread
analogy, this would have rendered them more sensitive to irritation, or
would by itself have excited movement; but no effect was produced. We
may, therefore, conclude that animals enter merely by forcing their way
through the slit-like orifice; their heads serving as a wedge. But I am
surprised that such small and weak creatures as are often captured (for
instance, the nauplius of a crustacean, and a tardigrade) should be
strong enough to act in this manner, seeing that it was difficult to
push in one end of a bit of a hair 1/4 of an inch in length.
Nevertheless, it is certain that weak and small creatures do enter, and
Mrs. Treat, of New Jersey, has been more successful than any other
observer, and has often witnessed in the case of Utricularia
clandestina the whole process.* She saw a tardigrade slowly walking
round a bladder, as if reconnoitring; at last it crawled into the
depression where the valve lies, and then easily entered. She also
witnessed the entrapment of various minute crustaceans. Cypris “was
quite wary, but nevertheless was often caught. Coming to the entrance
of a bladder, it would sometimes pause a moment, and then dash away; at
other times it would come close up, and even venture part of the way
into the entrance and back out as if afraid. Another, more heedless,
would open the door and walk in; but it was no sooner in than it
manifested alarm, drew in its feet and antennæ, and closed its shell.”
Larvæ, apparently of gnats, when “feeding near the entrance, are pretty
certain to run their heads into the net, whence there is no retreat. A
large larva is sometimes three or four hours in being swallowed, the
process bringing to

* ‘New York Tribune,’ reprinted in the ‘Gard. Chron.’ 1875, p. 303.
[page 409]


mind what I have witnessed when a small snake makes a large frog its
victim.” But as the valve does not appear to be in the least irritable,
the slow swallowing process must be the effect of the onward movement
of the larva.

It is difficult to conjecture what can attract so many creatures,
animal- and vegetable-feeding crustaceans, worms, tardigrades, and
various larvæ, to enter the bladders. Mrs. Treat says that the larvæ
just referred to are vegetable-feeders, and seem to have a special
liking for the long bristles round the valve, but this taste will not
account for the entrance of animal-feeding crustaceans. Perhaps small
aquatic animals habitually try to enter every small crevice, like that
between the valve and collar, in search of food or protection. It is
not probable that the remarkable transparency of the valve is an
accidental circumstance, and the spot of light thus formed may serve as
a guide. The long bristles round the entrance apparently serve for the
same purpose. I believe that this is the case, because the bladders of
some epiphytic and marsh species of Utricularia which live embedded
either in entangled vegetation or in mud, have no bristles round the
entrance, and these under such conditions would be of no service as a
guide. Nevertheless, with these epiphytic and marsh species, two pairs
of bristles project from the surface of the valve, as in the aquatic
species; and their use probably is to prevent too large animals from
trying to force an entrance into the bladder, thus rupturing orifice.

As under favourable circumstances most of the bladders succeed in
securing prey, in one case as many as ten crustaceans;—as the valve is
so well fitted to [page 410] allow animals to enter and to prevent
their escape;—and as the inside of the bladder presents so singular a
structure, clothed with innumerable quadrifid and bifid processes, it
is impossible to doubt that the plant has been specially adapted for
securing prey. From the analogy of Pinguicula, belonging to the same
family, I naturally expected that the bladders would have digested
their prey; but this is not the case, and there are no glands fitted
for secreting the proper fluid. Nevertheless, in order to test their
power of digestion, minute fragments of roast meat, three small cubes
of albumen, and three of cartilage, were pushed through the orifice
into the bladders of vigorous plants. They were left from one day to
three days and a half within, and the bladders were then cut open; but
none of the above substances exhibited the least signs of digestion or
dissolution; the angles of the cubes being as sharp as ever. These
observations were made subsequently to those on Drosera, Dionaea,
Drosophyllum, and Pinguicula; so that I was familiar with the
appearance of these substances when undergoing the early and final
stages of digestion. We may therefore conclude that Utricularia cannot
digest the animals which it habitually captures.

In most of the bladders the captured animals are so much decayed that
they form a pale brown, pulpy mass, with their chitinous coats so
tender that they fall to pieces with the greatest ease. The black
pigment of the eye-spots is preserved better than anything else. Limbs,
jaws, &c. are often found quite detached; and this I suppose is the
result of the vain struggles of the later captured animals. I have
sometimes felt surprised at the small proportion of imprisoned animals
in a fresh state compared with those utterly decayed. Mrs. Treat states
with respect [page 411] to the larvæ above referred to, that “usually
in less than two days after a large one was captured the fluid contents
of the bladders began to assume a cloudy or muddy appearance, and often
became so dense that the outline of the animal was lost to view.” This
statement raises the suspicion that the bladders secrete some ferment
hastening the process of decay. There is no inherent improbability in
this supposition, considering that meat soaked for ten minutes in water
mingled with the milky juice of the papaw becomes quite tender and soon
passes, as Browne remarks in his ‘Natural History of Jamaica,’ into a
state of putridity.

Whether or not the decay of the imprisoned animals is an any way
hastened, it is certain that matter is absorbed from them by the
quadrifid and bifid processes. The extremely delicate nature of the
membrane of which these processes are formed, and the large surface
which they expose, owing to their number crowded over the whole
interior of the bladder, are circumstances all favouring the process of
absorption. Many perfectly clean bladders which had never caught any
prey were opened, and nothing could be distinguished with a No. 8
object-glass of Hartnack within the delicate, structureless
protoplasmic lining of the arms, excepting in each a single yellowish
particle or modified nucleus. Sometimes two or even three such
particles were present; but in this case traces of decaying matter
could generally be detected. On the other hand, in bladders containing
either one large or several small decayed animals, the processes
presented a widely different appearance. Six such bladders were
carefully examined; one contained an elongated, coiled-up larva;
another a single large entomostracan crustacean, and the others from
two to five smaller ones, all [page 412] in a decayed state. In these
six bladders, a large number of the quadrifid processes contained
transparent, often yellowish, more or less confluent, spherical or
irregularly shaped, masses of matter. Some of the processes, however,
contained only fine granular matter, the particles of which were so
small that they could not be defined clearly with No. 8 of Hartnack.
The delicate layer of protoplasm lining their walls was in some cases a
little shrunk. On three occasions the above small masses of matter were
observed and sketched at short intervals of time; and they certainly
changed their positions relatively to each other and to the walls of
the arms. Separate masses sometimes became confluent, and then again
divided. A single little mass would send out a projection, which after
a time separated itself. Hence there could be no doubt that these
masses consisted of protoplasm. Bearing in mind that many clean
bladders were examined with equal care, and that these presented no
such appearance, we may confidently believe that the protoplasm in the
above cases had been generated by the absorption of nitrogenous matter
from the decaying animals. In two or three other bladders, which at
first appeared quite clean, on careful search a few processes were
found, with their outsides clogged with a little brown matter, showing
that some minute animal had been captured and had decayed, and the arms
here included a very few more or less spherical and aggregated masses;
the processes in other parts of the bladders being empty and
transparent. On the other hand, it must be stated that in three
bladders containing dead crustaceans, the processes were likewise
empty. This fact may be accounted for by the animals not having been
sufficiently decayed, or by time enough not having been allowed for the
generation of proto- [page 413] plasm, or by its subsequent absorption
and transference to other parts of the plant. It will hereafter be seen
that in three or four other species of Utricularia the quadrifid
processes in contact with decaying animals likewise contained
aggregated masses of protoplasm.

On the Absorption of certain Fluids by the Quadrifid and Bifid
processes.—These experiments were tried to ascertain whether certain
fluids, which seemed adapted for the purpose, would produce the same
effects on the processes as the absorption of decayed animal matter.
Such experiments are, however, troublesome; for it is not sufficient
merely to place a branch in the fluid, as the valve shuts so closely
that the fluid apparently does not enter soon, if at all. Even when
bristles were pushed into the orifices, they were in several cases
wrapped so closely round by the thin flexible edge of the valve that
the fluid was apparently excluded; so that the experiments tried in
this manner are doubtful and not worth giving. The best plan would have
been to puncture the bladders, but I did not think of this till too
late, excepting in a few cases. In all such trials, however, it cannot
be ascertained positively that the bladder, though translucent, does
not contain some minute animal in the last stage of decay. Therefore
most of my experiments were made by cutting bladders longitudinally
into two; the quadrifids were examined with No. 8 of Hartnack, then
irrigated, whilst under the covering glass, with a few drops of the
fluid under trial, kept in a damp chamber, and re-examined after stated
intervals of time with the same power as before.

[Four bladders were first tried as a control experiment, in the manner
just described, in a solution of one part of gum arabic to 218 of
water, and two bladders in a solution of one part of sugar to 437 of
water; and in neither case was any [page 414] change perceptible in the
quadrifids or bifids after 21 hrs. Four bladders were then treated in
the same manner with a solution of one part of nitrate of ammonia to
437 of water, and re-examined after 21 hrs. In two of these the
quadrifids now appeared full of very finely granular matter, and their
protoplasmic lining or primordial utricle was a little shrunk. In the
third bladder, the quadrifids included distinctly visible granules, and
the primordial utricle was a little shrunk after only 8 hrs. In the
fourth bladder the primordial utricle in most of the processes was here
and there thickened into little, irregular, yellowish specks; and from
the gradations which could be traced in this and other cases, these
specks appear to give rise to the larger free granules contained within
some of the processes. Other bladders, which, as far as could be
judged, had never caught any prey, were punctured and left in the same
solution for 17 hrs.; and their quadrifids now contained very fine
granular matter.

A bladder was bisected, examined, and irrigated with a solution of one
part of carbonate of ammonia to 437 of water. After 8 hrs. 30 m. the
quadrifids contained a good many granules, and the primordial utricle
was somewhat shrunk; after 23 hrs. the quadrifids and bifids contained
many spheres of hyaline matter, and in one arm twenty-four such spheres
of moderate size were counted. Two bisected bladders, which had been
previously left for 21 hrs. in the solution of gum (one part to 218 of
water) without being affected, were irrigated with the solution of
carbonate of ammonia; and both had their quadrifids modified in nearly
the same manner as just described,—one after only 9 hrs., and the other
after 24 hrs. Two bladders which appeared never to have caught any prey
were punctured and placed in the solution; the quadrifids of one were
examined after 17 hrs., and found slightly opaque; the quadrifids of
the other, examined after 45 hrs., had their primordial utricles more
or less shrunk with thickened yellowish specks, like those due to the
action of nitrate of ammonia. Several uninjured bladders were left in
the same solution, as well as a weaker solution of one part to 1750 of
water, or 1 gr. to 4 oz.; and after two days the quadrifids were more
or less opaque, with their contents finely granular; but whether the
solution had entered by the orifice, or had been absorbed from the
outside, I know not.

Two bisected bladders were irrigated with a solution of one part of
urea to 218 of water; but when this solution was employed, I forgot
that it had been kept for some days in a warm room, and had therefore
probably generated ammonia; anyhow [page 415] the quadrifids were
affected after 21 hrs. as if a solution of carbonate of ammonia had
been used; for the primordial utricle was thickened in specks, which
seemed to graduate into separate granules. Three bisected bladders were
also irrigated with a fresh solution of urea of the same strength;
their quadrifids after 21 hrs. were much less affected than in the
former case; nevertheless, the primordial utricle in some of the arms
was a little shrunk, and in others was divided into two almost
symmetrical sacks.

Three bisected bladders, after being examined, were irrigated with a
putrid and very offensive infusion of raw meat. After 23 hrs. the
quadrifids and bifids in all three specimens abounded with minute,
hyaline, spherical masses; and some of their primordial utricles were a
little shrunk. Three bisected bladders were also irrigated with a fresh
infusion of raw meat; and to my surprise the quadrifids in one of them
appeared, after 23 hrs., finely granular, with their primordial
utricles somewhat shrunk and marked with thickened yellowish specks; so
that they had been acted on in the same manner as by the putrid
infusion or by the salts of ammonia. In the second bladder some of the
quadrifids were similarly acted on, though to a very slight degree;
whilst the third bladder was not at all affected.]

From these experiments it is clear that the quadrifid and bifid
processes have the power of absorbing carbonate and nitrate of ammonia,
and matter of some kind from a putrid infusion of meat. Salts of
ammonia were selected for trial, as they are known to be rapidly
generated by the decay of animal matter in the presence of air and
water, and would therefore be generated within the bladders containing
captured prey. The effect produced on the processes by these salts and
by a putrid infusion of raw meat differs from that produced by the
decay of the naturally captured animals only in the aggregated masses
of protoplasm being in the latter case of larger size; but it is
probable that the fine granules and small hyaline spheres produced by
the solutions would coalesce into larger masses, with time enough
allowed. [page 416] We have seen with Drosera that the first effect of
a weak solution of carbonate of ammonia on the cell-contents is the
production of the finest granules, which afterwards aggregate into
larger, more or less rounded, masses; and that the granules in the
layer of protoplasm which flows round the walls ultimately coalesce
with these masses. Changes of this nature are, however, far more rapid
in Drosera than in Utricularia. Since the bladders have no power of
digesting albumen, cartilage, or roast meat, I was surprised that
matter was absorbed, at least in one case, from a fresh infusion of raw
meat. I was also surprised, from what we shall presently see with
respect to the glands round the orifice, that a fresh solution of urea
produced only a moderate effect on the quadrifids.

As the quadrifids are developed from papillae which at first closely
resemble those on the outside of the bladders and on the surfaces of
the leaves, I may here state that the two hemispherical cells with
which these latter papillae are crowned, and which in their natural
state are perfectly transparent, likewise absorb carbonate and nitrate
of ammonia; for, after an immersion of 23 hrs. in solutions of one part
of both these salts to 437 of water, their primordial utricles were a
little shrunk and of a pale brown tint, and sometimes finely granular.
The same result followed from the immersion of a whole branch for
nearly three days in a solution of one part of the carbonate to 1750 of
water. The grains of chlorophyll, also, in the cells of the leaves on
this branch became in many places aggregated into little green masses,
which were often connected together by the finest threads.

On the Absorption of certain Fluids by the Glands on the Valve and
Collar.—The glands round the orifices of bladders which are still
young, or which have been [page 417] long kept in moderately pure
water, are colourless; and their primordial utricles are only slightly
or hardly at all granular. But in the greater number of plants in a
state of nature—and we must remember that they generally grow in very
foul water—and with plants kept in an aquarium in foul water, most of
the glands were of a pale brownish tint; their primordial utricles were
more or less shrunk, sometimes ruptured, with their contents often
coarsely granular or aggregated into little masses. That this state of
the glands is due to their having absorbed matter from the surrounding
water, I cannot doubt; for, as we shall immediately see, nearly the
same results follow from their immersion for a few hours in various
solutions. Nor is it probable that this absorption is useless, seeing
that it is almost universal with plants growing in a state of nature,
excepting when the water is remarkably pure.

The pedicels of the glands which are situated close to the slit-like
orifice, both those on the valve and on the collar, are short; whereas
the pedicels of the more distant glands are much elongated and project
inwards. The glands are thus well placed so to be washed by any fluid
coming out of the bladder through the orifice. The valve fits so
closely, judging from the result of immersing uninjured bladders in
various solutions, that it is doubtful whether any putrid fluid
habitually passes outwards. But we must remember that a bladder
generally captures several animals; and that each time a fresh animal
enters, a puff of foul water must pass out and bathe the glands.
Moreover, I have repeatedly found that, by gently pressing bladders
which contained air, minute bubbles were driven out through the
orifice; and if a bladder is laid on blotting paper and gently pressed,
water oozes out. [page 418] In this latter case, as soon as the
pressure is relaxed, air is drawn in, and the bladder recovers its
proper form. If it is now placed under water and again gently pressed,
minute bubbles issue from the orifice and nowhere else, showing that
the walls of the bladder have not been ruptured. I mention this because
Cohn quotes a statement by Treviranus, that air cannot be forced out of
a bladder without rupturing it. We may therefore conclude that whenever
air is secreted within a bladder already full of water, some water will
be slowly driven out through the orifice. Hence I can hardly doubt that
the numerous glands crowded round the orifice are adapted to absorb
matter from the putrid water, which will occasionally escape from
bladders including decayed animals.

[In order to test this conclusion, I experimented with various
solutions on the glands. As in the case of the quadrifids, salts of
ammonia were tried, since these are generated by the final decay of
animal matter under water. Unfortunately the glands cannot be carefully
examined whilst attached to the bladders in their entire state. Their
summits, therefore, including the valve, collar, and antennæ, were
sliced off, and the condition of the glands observed; they were then
irrigated, whilst beneath a covering glass, with the solutions, and
after a time re-examined with the same power as before, namely No. 8 of
Hartnack. The following experiments were thus made.

As a control experiment solutions of one part of white sugar and of one
part of gum to 218 of water were first used, to see whether these
produced any change in the glands. It was also necessary to observe
whether the glands were affected by the summits of the bladders having
been cut off. The summits of four were thus tried; one being examined
after 2 hrs. 30 m., and the other three after 23 hrs.; but there was no
marked change in the glands of any of them.

Two summits bearing quite colourless glands were irrigated with a
solution of carbonate of ammonia of the same strength (viz. one part to
218 of water) , and in 5 m. the primordial utricles of most of the
glands were somewhat contracted; they were also thickened in specks or
patches, and had assumed a pale [page 419] brown tint. When looked at
again after 1 hr. 30 m., most of them presented a somewhat different
appearance. A third specimen was treated with a weaker solution of one
part of the carbonate to 437 of water, and after 1 hr. the glands were
pale brown and contained numerous granules.

Four summits were irrigated with a solution of one part of nitrate of
ammonia to 437 of water. One was examined after 15 m., and the glands
seemed affected; after 1 hr. 10 m. there was a greater change, and the
primordial utricles in most of them were somewhat shrunk, and included
many granules. In the second specimen, the primordial utricles were
considerably shrunk and brownish after 2 hrs. Similar effects were
observed in the two other specimens, but these were not examined until
21 hrs. had elapsed. The nuclei of many of the glands apparently had
increased in size. Five bladders on a branch, which had been kept for a
long time in moderately pure water, were cut off and examined, and
their glands found very little modified. The remainder of this branch
was placed in the solution of the nitrate, and after 21 hrs. two
bladders were examined, and all their glands were brownish, with their
primordial utricles somewhat shrunk and finely granular.

The summit of another bladder, the glands of which were in a
beautifully clear condition, was irrigated with a few drops of a mixed
solution of nitrate and phosphate of ammonia, each of one part to 437
of water. After 2 hrs. some few of the glands were brownish. After 8
hrs. almost all the oblong glands were brown and much more opaque than
they were before; their primordial utricles were somewhat shrunk and
contained a little aggregated granular matter. The spherical glands
were still white, but their utricles were broken up into three or four
small hyaline spheres, with an irregularly contracted mass in the
middle of the basal part. These smaller spheres changed their forms in
the course of a few hours and some of them disappeared. By the next
morning, after 23 hrs. 30 m., they had all disappeared, and the glands
were brown; their utricles now formed a globular shrunken mass in the
middle. The utricles of the oblong glands had shrunk very little, but
their contents were somewhat aggregated. Lastly, the summit of a
bladder which had been previously irrigated for 21 hrs. with a solution
of one part of sugar to 218 of water without being affected, was
treated with the above mixed solution; and after 8 hrs. 30 m. all the
glands became brown, with their primordial utricles slightly shrunk.

Four summits were irrigated with a putrid infusion of raw [page 420]
meat. No change in the glands was observable for some hours, but after
24 hrs. most of them had become brownish, and more opaque and granular
than they were before. In these specimens, as in those irrigated with
the salts of ammonia, the nuclei seemed to have increased both in size
and solidity, but they were not measured. Five summits were also
irrigated with a fresh infusion of raw meat; three of these were not at
all affected in 24 hrs., but the glands of the other two had perhaps
become more granular. One of the specimens which was not affected was
then irrigated with the mixed solution of the nitrate and phosphate of
ammonia, and after only 25 m. the glands contained from four or five to
a dozen granules. After six additional hours their primordial utricles
were greatly shrunk.

The summit of a bladder was examined, and all the glands found
colourless, with their primordial utricles not at all shrunk; yet many
of the oblong glands contained granules just resolvable with No. 8 of
Hartnack. It was then irrigated with a few drops of a solution of one
part of urea to 218 of water. After 2 hrs. 25 m. the spherical glands
were still colourless; whilst the oblong and two-armed ones were of a
brownish tint, and their primordial utricles much shrunk, some
containing distinctly visible granules. After 9 hrs. some of the
spherical glands were brownish, and the oblong glands were still more
changed, but they contained fewer separate granules; their nuclei, on
the other hand, appeared larger, as if they had absorbed the granules.
After 23 hrs. all the glands were brown, their primordial utricles
greatly shrunk, and in many cases ruptured.

A bladder was now experimented on, which was already somewhat affected
by the surrounding water; for the spherical glands, though colourless,
had their primordial utricles slightly shrunk; and the oblong glands
were brownish, with their utricles much, but irregularly, shrunk. The
summit was treated with the solution of urea, but was little affected
by it in 9 hrs.; nevertheless, after 23 hrs. the spherical glands were
brown, with their utricles more shrunk; several of the other glands
were still browner, with their utricles contracted into irregular
little masses.

Two other summits, with their glands colourless and their utricles not
shrunk, were treated with the same solution of urea. After 5 hrs. many
of the glands presented a shade of brown, with their utricles slightly
shrunk. After 20 hrs. 40 m. some few of them were quite brown, and
contained [page 421] irregularly aggregated masses; others were still
colourless, though their utricles were shrunk; but the greater number
were not much affected. This was a good instance of how unequally the
glands on the same bladder are sometimes affected, as likewise often
occurs with plants growing in foul water. Two other summits were
treated with a solution which had been kept during several days in a
warm room, and their glands were not at all affected when examined
after 21 hrs.

A weaker solution of one part of urea to 437 of water was next tried on
six summits, all carefully examined before being irrigated. The first
was re-examined after 8 hrs. 30 m., and the glands, including the
spherical ones, were brown; many of the oblong glands having their
primordial utricles much shrunk and including granules. The second
summit, before being irrigated, had been somewhat affected by the
surrounding water, for the spherical glands were not quite uniform in
appearance; and a few of the oblong ones were brown, with their
utricles shrunk. Of the oblong glands, those which were before
colourless, became brown in 3 hrs. 12 m. after irrigation, with their
utricles slightly shrunk. The spherical glands did not become brown,
but their contents seemed changed in appearance, and after 23 hrs.
still more changed and granular. Most of the oblong glands were now
dark brown, but their utricles were not greatly shrunk. The four other
specimens were examined after 3 hrs. 30 m., after 4 hrs., and 9 hrs.; a
brief account of their condition will be sufficient. The spherical
glands were not brown, but some of them were finely granular. Many of
the oblong glands were brown, and these, as well as others which still
remained colourless, had their utricles more or less shrunk, some of
them including small aggregated masses of matter.]

A Summary of the Observations on Absorption.—From the facts now given
there can be no doubt that the variously shaped glands on the valve and
round the collar have the power of absorbing matter from weak solutions
of certain salts of ammonia and urea, and from a putrid infusion of raw
meat. Prof. Cohn believes that they secrete slimy matter; but I was not
able to perceive any trace of such action, excepting that, after
immersion in alcohol, extremely fine lines could sometimes be seen
radiating from their [page 422] surfaces. The glands are variously
affected by absorption; they often become of a brown colour; sometimes
they contain very fine granules, or moderately sized grains, or
irregularly aggregated little masses; sometimes the nuclei appear to
have increased in size; the primordial utricles are generally more or
less shrunk and sometimes ruptured. Exactly the same changes may be
observed in the glands of plants growing and flourishing in foul water.
The spherical glands are generally affected rather differently from the
oblong and two-armed ones. The former do not so commonly become brown,
and are acted on more slowly. We may therefore infer that they differ
somewhat in their natural functions.

It is remarkable how unequally the glands on the bladders on the same
branch, and even the glands of the same kind on the same bladder, are
affected by the foul water in which the plants have grown, and by the
solutions which were employed. In the former case I presume that this
is due either to little currents bringing matter to some glands and not
to others, or to unknown differences in their constitution. When the
glands on the same bladder are differently affected by a solution, we
may suspect that some of them had previously absorbed a small amount of
matter from the water. However this may be, we have seen that the
glands on the same leaf of Drosera are sometimes very unequally
affected, more especially when exposed to certain vapours.

If glands which have already become brown, with their primordial
utricles shrunk, are irrigated with one of the effective solutions,
they are not acted on, or only slightly and slowly. If, however, a
gland contains merely a few coarse granules, this does not prevent a
solution from acting. I have never seen [page 423] any appearance
making it probable that glands which have been strongly affected by
absorbing matter of any kind are capable of recovering their pristine,
colourless, and homogeneous condition, and of regaining the power of
absorbing.

From the nature of the solutions which were tried, I presume that
nitrogen is absorbed by the glands; but the modified, brownish, more or
less shrunk, and aggregated contents of the oblong glands were never
seen by me or by my son to undergo those spontaneous changes of form
characteristic of protoplasm. On the other hand, the contents of the
larger spherical glands often separated into small hyaline globules or
irregularly shaped masses, which changed their forms very slowly and
ultimately coalesced, forming a central shrunken mass. Whatever may be
the nature of the contents of the several kinds of glands, after they
have been acted on by foul water or by one of the nitrogenous
solutions, it is probable that the matter thus generated is of service
to the plant, and is ultimately transferred to other parts.

The glands apparently absorb more quickly than do the quadrifid and
bifid processes; and on the view above maintained, namely that they
absorb matter from putrid water occasionally emitted from the bladders,
they ought to act more quickly than the processes; as these latter
remain in permanent contact with captured and decaying animals.

Finally, the conclusion to which we are led by the foregoing
experiments and observations is that the bladders have no power of
digesting animal matter, though it appears that the quadrifids are
somewhat affected by a fresh infusion of raw meat. It is certain that
the processes within the bladders, and the glands outside, absorb
matter from salts of [page 424] ammonia, from a putrid infusion of raw
meat, and from urea. The glands apparently are acted on more strongly
by a solution of urea, and less strongly by an infusion of raw meat,
than are the processes. The case of urea is particularly interesting,
because we have seen that it produces no effect on Drosera, the leaves
of which are adapted to digest fresh animal matter. But the most
important fact of all is, that in the present and following species the
quadrifid and bifid processes of bladders containing decayed animals
generally include little masses of spontaneously moving protoplasm;
whilst such masses are never seen in perfectly clean bladders.

Development of the Bladders.—My son and I spent much time over this
subject with small success. Our observations apply to the present
species and to Utricularia vulgaris, but were made chiefly on the
latter, as the bladders are twice as large as those of Utricularia
neglecta. In the early part of autumn the stems terminate in large
buds, which fall off and lie dormant during the winter at the bottom.
The young leaves forming these buds bear bladders in various stages of
early development. When the bladders of Utricularia vulgaris are about
1/100 inch (.254 mm.) in diameter (or 1/200 in the case of Utricularia
neglecta), they are circular in outline, with a narrow, almost closed,
transverse orifice, leading into a hollow filled with water; but the
bladders are hollow when much under 1/100 of an inch in diameter. The
orifices face inwards or towards the axis of the plant. At this early
age the bladders are flattened in the plane in which the orifice lies,
and therefore at right angles to that of the mature bladders. They are
covered exteriorly with papillae of different sizes, many of which have
an elliptical outline. A bundle of vessels, formed of [page 425] simple
elongated cells, runs up the short footstalk, and divides at the base
of the bladder. One branch extends up the middle of the dorsal surface,
and the other up the middle of the ventral surface. In full-grown
bladders the ventral bundle divides close beneath the collar, and the
two branches run on each side to near where the corners of the valve
unite with the collar; but these branches could not be seen in very
young bladders.

FIG. 23. (Utricularia vulgaris.) Longitudinal section through a young
bladder, 1/100 of an inch in length, with the orifice too widely open.

The accompanying figure (fig. 23) shows a section, which happened to be
strictly medial, through the footstalk and between the nascent antennæ
of a bladder of Utricularia vulgaris, 1/100 inch in diameter. The
specimen was soft, and the young valve became separated from the collar
to a greater degree than is natural, and is thus represented. We here
clearly see that the valve and collar are infolded prolongations of the
walls of the bladder. Even at this early age, glands could be detected
on the valve. The state of the quadrifid processes will presently be
described. The antennæ at this period consist of minute cellular
projections (not shown in the above figure, as they do not lie in the
medial plane), which soon bear incipient bristles. In five instances
the young antennæ were not of quite equal length; and this fact is
intelligible if I am right in believing that they represent two
divisions of the leaf, rising from the end of the bladder; for, with
the true leaves, whilst very young, the divisions are never, as far as
I have seen, strictly opposite; they [page 426] must therefore be
developed one after the other, and so it would be with the two antennæ.

At a much earlier age, when the half formed bladders are only 1/300
inch (.0846 mm.) in diameter or a little more, they present a totally
different appearance. One is represented on the left side of the
accompanying drawing (fig. 24). The young leaves

FIG. 24. (Utricularia vulgaris.) Young leaf from a winter bud, showing
on the left side a bladder in its earliest stage of development.

at this age have broad flattened segments, with their future divisions
represented by prominences, one of which is shown on the right side.
Now, in a large number of specimens examined by my son, the young
bladders appeared as if formed by the oblique folding over of the apex
and of one margin with a prominence, against the opposite margin. The
circular hollow between the infolded apex and infolded prominence
apparently contracts into the narrow orifice, wherein the valve and
collar will be developed; the bladder itself being formed by the
confluence of the opposed [page 427] margins of the rest of the leaf.
But strong objections may be urged against this view, for we must in
this case suppose that the valve and collar are developed
asymmetrically from the sides of the apex and prominence. Moreover, the
bundles of vascular tissue have to be formed in lines quite
irrespective of the original form of the leaf. Until gradations can be
shown to exist between this the earliest state and a young yet perfect
bladder, the case must be left doubtful.

As the quadrifid and bifid processes offer one of the greatest
peculiarities in the genus, I carefully observed their development in
Utricularia neglecta. In bladders about 1/100 of an inch in diameter,
the inner surface is studded with papillae, rising from small cells at
the junctions of the larger ones. These papillae consist of a delicate
conical protuberance, which narrows into a very short footstalk,
surmounted by two minute cells. They thus occupy the same relative
position, and closely resemble, except in being smaller and rather more
prominent, the papillae on the outside of the bladders, and on the
surfaces of the leaves. The two terminal cells of the papillae first
become much elongated in a line parallel to the inner surface of the
bladder. Next, each is divided by a longitudinal partition. Soon the
two half-cells thus formed separate from one another; and we now have
four cells or an incipient quadrifid process. As there is not space for
the two new cells to increase in breadth in their original plane, the
one slides partly under the other. Their manner of growth now changes,
and their outer sides, instead of their apices, continue to grow. The
two lower cells, which have slid partly beneath the two upper ones,
form the longer and more upright pair of processes; whilst the two
upper cells form the shorter [page 428] and more horizontal pair; the
four together forming a perfect quadrifid. A trace of the primary
division between the two cells on the summits of the papillae can still
be seen between the bases of the longer processes. The development of
the quadrifids is very liable to be arrested. I have seen a bladder
1/50 of an inch in length including only primordial papillae; and
another bladder, about half its full size, with the quadrifids in an
early stage of development.

As far as I could make out, the bifid processes are developed in the
same manner as the quadrifids, excepting that the two primary terminal
cells never become divided, and only increase in length. The glands on
the valve and collar appear at so early an age that I could not trace
their development; but we may reasonably suspect that they are
developed from papillae like those on the outside of the bladder, but
with their terminal cells not divided into two. The two segments
forming the pedicels of the glands probably answer to the conical
protuberance and short footstalk of the quadrifid and bifid processes.
I am strengthened in the belief that the glands are developed from
papillae like those on the outside of the bladders, from the fact that
in Utricularia amethystina the glands extend along the whole ventral
surface of the bladder close to the footstalk.

UTRICULARIA VULGARIS.


Living plants from Yorkshire were sent me by Dr. Hooker. This species
differs from the last in the stems and leaves being thicker or coarser;
their divisions form a more acute angle with one another; the notches
on the leaves bear three or four short bristles instead of one; and the
bladders are twice as large, or about 1/5 of an inch (5.08 mm.) in
diameter. In all essential respects the bladders resemble those of
Utricularia neglecta, but the sides of the peristome are perhaps a
little more [page 429] prominent, and always bear, as far as I have
seen, seven or eight long multicellular bristles. There are eleven long
bristles on each antenna, the terminal pair being included. Five
bladders, containing prey of some kind, were examined. The first
included five Cypris; a large copepod and a Diaptomus; the second, four
Cypris; the third, a single rather large crustacean; the fourth, six
crustaceans; and the fifth, ten. My son examined the quadrifid
processes in a bladder containing the remains of two crustaceans, and
found some of them full of spherical or irregularly shaped masses of
matter, which were observed to move and to coalesce. These masses
therefore consisted of protoplasm.

UTRICULARIA MINOR.


FIG. 25. (Utricularia minor.) Quadrifid process, greatly enlarged.

This rare species was sent me in a living state from Cheshire, through
the kindness of Mr. John Price. The leaves and bladders are much
smaller than those of Utricularia neglecta. The leaves bear fewer and
shorter bristles, and the bladders are more globular. The antennæ,
instead of projecting in front of the bladders, are curled under the
valve, and are armed with twelve or fourteen extremely long
multicellular bristles, generally arranged in pairs. These, with seven
or eight long bristles on both sides of the peristome, form a sort of
net over the valve, which would tend to prevent all animals, excepting
very small ones, entering the bladder. The valve and collar have the
same essential structure as in the two previous species; but the glands
are not quite so numerous; the oblong ones are rather more elongated,
whilst the two-armed ones are rather less elongated. The four bristles
which project obliquely from the lower edge of the valve are short.
Their shortness, compared with those on the valves of the foregoing
species, is intelligible if my view is correct that they serve to
prevent too large animals forcing an entrance through the valve, thus
injuring it; for the valve is already protected to a certain extent by
the incurved antennæ, together with the lateral bristles. The bifid
processes are like those in the previous species; but the quadrifids
differ in the four arms (fig. 25) [page 430] being directed to the same
side; the two longer ones being central, and the two shorter ones on
the outside.

The plants were collected in the middle of July; and the contents of
five bladders, which from their opacity seemed full of prey, were
examined. The first contained no less than twenty-four minute
fresh-water crustaceans, most of them consisting of empty shells, or
including only a few drops of red oily matter; the second contained
twenty; the third, fifteen; the fourth, ten, some of them being rather
larger than usual; and the fifth, which seemed stuffed quite full,
contained only seven, but five of these were of unusually large size.
The prey, therefore, judging from these five bladders, consists
exclusively of fresh-water crustaceans, most of which appeared to be
distinct species from those found in the bladders of the two former
species. In one bladder the quadrifids in contact with a decaying mass
contained numerous spheres of granular matter, which slowly changed
their forms and positions.

UTRICULARIA CLANDESTINA.


This North American species, which is aquatic like the three foregoing
ones, has been described by Mrs. Treat, of New Jersey, whose excellent
observations have already been largely quoted. I have not as yet seen
any full description by her of the structure of the bladder, but it
appears to be lined with quadrifid processes. A vast number of captured
animals were found within the bladders; some being crustaceans, but the
greater number delicate, elongated larvæ, I suppose of Culicidae. On
some stems, “fully nine out of every ten bladders contained these larvæ
or their remains.” The larvæ “showed signs of life from twenty-four to
thirty-six hours after being imprisoned,” and then perished. [page 431]




CHAPTER XVIII.
UTRICULARIA (continued).


Utricularia montana—Description of the bladders on the subterranean
rhizomes—Prey captured by the bladders of plants under culture and in a
state of nature—Absorption by the quadrifid processes and glands—Tubers
serving as reservoirs for water—Various other species of
Utricularia—Polypompholyx—Genlisea, different nature of the trap for
capturing prey— Diversified methods by which plants are nourished.


FIG. 26. (Utricularia montana.) Rhizome swollen into a tuber; the
branches bearing minute bladders; of natural size.

Utricularia montana.—This species inhabits the tropical parts of South
America, and is said to be epiphytic; but, judging from the state of
the roots (rhizomes) of some dried specimens from the herbarium at Kew,
it likewise lives in earth, probably in crevices of rocks. In English
hothouses it is grown in peaty soil. Lady Dorothy Nevill was so kind as
to give me a fine plant, and I received another from Dr. Hooker. The
leaves are entire, instead of being much divided, as in the foregoing
aquatic species. They are elongated, about 1 1/2 inch in breadth, and
furnished with a distinct footstalk. The plant produces numerous
colourless rhizomes, as thin as threads, which bear minute bladders,
and occasionally swell into tubers, as will [page 432] hereafter be
described. These rhizomes appear exactly like roots, but occasionally
throw up green shoots. They penetrate the earth sometimes to the depth
of more than 2 inches; but when the plant grows as an epiphyte, they
must creep amidst the mosses, roots, decayed bark, &c., with which the
trees of these countries are thickly covered.

As the bladders are attached to the rhizomes, they are necessarily
subterranean. They are produced in extraordinary numbers. One of my
plants, though young, must have borne several hundreds; for a single
branch out of an entangled mass had thirty-two, and another branch,
about 2 inches in length (but with its end and one side branch broken
off), had seventy- three bladders.* The bladders are compressed and
rounded, with the ventral surface, or that between the summit of the
long delicate footstalk and valve, extremely short (fig. 27). They are
colourless and almost as transparent as glass, so that they appear
smaller than they really are, the largest being under the 1/20 of an
inch (1.27 mm.) in its longer diameter. They are formed of rather large
angular cells, at the junctions of which oblong papillae project,
corresponding with those on the surfaces of the bladders of the
previous species. Similar papillae abound on the rhizomes, and even on
the entire leaves, but they are rather broader on the latter. Vessels,
marked with parallel bars instead of by a spiral line, run up the
footstalks, and

* Prof. Oliver has figured a plant of Utricularia Jamesoniana (‘Proc.
Linn. Soc.’ vol. iv. p. 169) having entire leaves and rhizomes, like
those of our present species; but the margins of the terminal halves of
some of the leaves are converted into bladders. This fact clearly
indicates that the bladders on the rhizomes of the present and
following species are modified segments of the leaf; and they are thus
brought into accordance with the bladders attached to the divided and
floating leaves of the aquatic species. [page 433]


just enter the bases of the bladders; but they do not bifurcate and
extend up the dorsal and ventral surfaces, as in the previous species.

The antennæ are of moderate length, and taper to a fine point; they
differ conspicuously from those before described, in not being armed
with bristles. Their bases are so abruptly curved that their tips
generally rest one on each side of the middle of the bladder, but

FIG. 27. (Utricularia montana.) Bladder; about 27 times enlarged.

sometimes near the margin. Their curved bases thus form a roof over the
cavity in which the valve lies; but there is always left on each side a
little circular passage into the cavity, as may be seen in the drawing,
as well as a narrow passage between the bases of the two antennæ. As
the bladders are subterranean, had it not been for the roof, the cavity
in which the valve lies would have been liable to be blocked up with
earth [page 434] and rubbish; so that the curvature of the antennæ is a
serviceable character. There are no bristles on the outside of the
collar or peristome, as in the foregoing species.

The valve is small and steeply inclined, with its free posterior edge
abutting against a semicircular, deeply depending collar. It is
moderately transparent, and bears two pairs of short stiff bristles, in
the same position as in the other species. The presence of these four
bristles, in contrast with the absence of those on the antennæ and
collar, indicates that they are of functional importance, namely, as I
believe, to prevent too large animals forcing an entrance through the
valve. The many glands of diverse shapes attached to the valve and
round the collar in the previous species are here absent, with the
exception of about a dozen of the two-armed or transversely elongated
kind, which are seated near the borders of the valve, and are mounted
on very short footstalks. These glands are only the 3/4000 of an inch
(.019 mm.) in length; though so small, they act as absorbents. The
collar is thick, stiff, and almost semi-circular; it is formed of the
same peculiar brownish tissue as in the former species.

The bladders are filled with water, and sometimes include bubbles of
air. They bear internally rather short, thick, quadrifid processes
arranged in approximately concentric rows. The two pairs of arms of
which they are formed differ only a little in length, and stand in a
peculiar position (fig. 28); the two longer ones forming one line, and
the two shorter ones another parallel line. Each arm includes a small
spherical mass of brownish matter, which, when crushed, breaks into
angular pieces. I have no doubt that these spheres are nuclei, for
closely similar ones [page 435] are present in the cells forming the
walls of the bladders. Bifid processes, having rather short oval arms,
arise in the usual position on the inner side of the collar.

These bladders, therefore, resemble in all essential respects the
larger ones of the foregoing species. They differ chiefly in the
absence of the numerous glands on the valve and round the collar, a few
minute ones of one kind alone being present on the valve. They differ
more conspicuously in the absence of the long bristles on the antennæ
and on the outside of the collar. The presence of these bristles in the
previously mentioned species probably relates to the capture of aquatic
animals.

FIG. 28. (Utricularia montana.) One of the quadrifid processes; much
enlarged.

It seemed to me an interesting question whether the minute bladders of
Utricularia montanaserved, as in the previous species, to capture
animals living in the earth, or in the dense vegetation covering the
trees on which this species is epiphytic; for in this case we should
have a new sub-class of carnivorous plants, namely, subterranean
feeders. Many bladders, therefore, were examined, with the following
results:—

[(1) A small bladder, less than 1/30 of an inch (.847 mm.) in diameter,
contained a minute mass of brown, much decayed matter; and in this, a
tarsus with four or five joints, terminating in a double hook, was
clearly distinguished under the microscope. I suspect that it was a
remnant of one of the Thysanoura. The quadrifids in contact with this
decayed remnant contained either small masses of translucent, yellowish
matter, generally more [page 436] or less globular, or fine granules.
In distant parts of the same bladder, the processes were transparent
and quite empty, with the exception of their solid nuclei. My son made
at short intervals of time sketches of one of the above aggregated
masses, and found that they continually and completely changed their
forms; sometimes separating from one another and again coalescing.
Evidently protoplasm had been generated by the absorption of some
element from the decaying animal matter.

(2) Another bladder included a still smaller speck of decayed brown
matter, and the adjoining quadrifids contained aggregated matter,
exactly as in the last case.

(3) A third bladder included a larger organism, which was so much
decayed that I could only make out that it was spinose or hairy. The
quadrifids in this case were not much affected, excepting that the
nuclei in the several arms differed much in size; some of them
containing two masses having a similar appearance.

(4) A fourth bladder contained an articulate organism, for I distinctly
saw the remnant of a limb, terminating in a hook. The quadrifids were
not examined.

(5) A fifth included much decayed matter apparently of some animal, but
with no recognisable features. The quadrifids in contact contained
numerous spheres of protoplasm.

(6) Some few bladders on the plant which I received from Kew were
examined; and in one, there was a worm-shaped animal very little
decayed, with a distinct remnant of a similar one greatly decayed.
Several of the arms of the processes in contact with these remains
contained two spherical masses, like the single solid nucleus which is
properly found in each arm. In another bladder there was a minute grain
of quartz, reminding me of two similar cases with Utricularia neglecta.

As it appeared probable that this plant would capture a greater number
of animals in its native country than under culture, I obtained
permission to remove small portions of the rhizomes from dried
specimens in the herbarium at Kew. I did not at first find out that it
was advisable to soak the rhizomes for two or three days, and that it
was necessary to open the bladders and spread out their contents on
glass; as from their state of decay and from having been dried and
pressed, their nature could not otherwise be well distinguished.
Several bladders on a plant which had grown in black earth in New
Granada were first examined; and four of these included remnants of
animals. The first contained a hairy Acarus, so much decayed that
nothing was left except its transparent coat; [page 437] also a yellow
chitinous head of some animal with an internal fork, to which the
oesophagus was suspended, but I could see no mandibles; also the double
hook of the tarsus of some animal; also an elongated greatly decayed
animal; and lastly, a curious flask-shaped organism, having the walls
formed of rounded cells. Professor Claus has looked at this latter
organism, and thinks that it is the shell of a rhizopod, probably one
of the Arcellidae. In this bladder, as well as in several others, there
were some unicellular Algae, and one multicellular Alga, which no doubt
had lived as intruders.

A second bladder contained an Acarus much less decayed than the former
one, with its eight legs preserved; as well as remnants of several
other articulate animals. A third bladder contained the end of the
abdomen with the two hinder limbs of an Acarus, as I believe. A fourth
contained remnants of a distinctly articulated bristly animal, and of
several other organisms, as well as much dark brown organic matter, the
nature of which could not be made out.

Some bladders from a plant, which had lived as an epiphyte in Trinidad,
in the West Indies, were next examined, but not so carefully as the
others; nor had they been soaked long enough. Four of them contained
much brown, translucent, granular matter, apparently organic, but with
no distinguishable parts. The quadrifids in two were brownish, with
their contents granular; and it was evident that they had absorbed
matter. In a fifth bladder there was a flask-shaped organism, like that
above mentioned. A sixth contained a very long, much decayed,
worm-shaped animal. Lastly, a seventh bladder contained an organism,
but of what nature could not be distinguished.]

Only one experiment was tried on the quadrifid processes and glands
with reference to their power of absorption. A bladder was punctured
and left for 24 hrs. in a solution of one part of urea to 437 of water,
and the quadrifid and bifid processes were found much affected. In some
arms there was only a single symmetrical globular mass, larger than the
proper nucleus, and consisting of yellowish matter, generally
translucent but sometimes granular; in others there were two masses of
different sizes, one large and the [page 438] other small; and in
others there were irregularly shaped globules; so that it appeared as
if the limpid contents of the processes, owing to the absorption of
matter from the solution, had become aggregated sometimes round the
nucleus, and sometimes into separate masses; and that these then tended
to coalesce. The primordial utricle or protoplasm lining the processes
was also thickened here and there into irregular and variously shaped
specks of yellowish translucent matter, as occurred in the case of
Utricularia neglecta under similar treatment. These specks apparently
did not change their forms.

The minute two-armed glands on the valve were also affected by the
solution; for they now contained several, sometimes as many as six or
eight, almost spherical masses of translucent matter, tinged with
yellow, which slowly changed their forms and positions. Such masses
were never observed in these glands in their ordinary state. We may
therefore infer that they serve for absorption. Whenever a little water
is expelled from a bladder containing animal remains (by the means
formerly specified, more especially by the generation of bubbles of
air), it will fill the cavity in which the valve lies; and thus the
glands will be able to utilise decayed matter which otherwise would
have been wasted.

Finally, as numerous minute animals are captured by this plant in its
native country and when cultivated, there can be no doubt that the
bladders, though so small, are far from being in a rudimentary
condition; on the contrary, they are highly efficient traps. Nor can
there be any doubt that matter is absorbed from the decayed prey by the
quadrifid and bifid processes, and that protoplasm is thus generated.
What tempts animals of such diverse kinds to enter [page 439] the
cavity beneath the bowed antennæ, and then force their way through the
little slit-like orifice between the valve and collar into the bladders
filled with water, I cannot conjecture.

Tubers.—These organs, one of which is represented in a previous figure
(fig. 26) of the natural size, deserve a few remarks. Twenty were found
on the rhizomes of a single plant, but they cannot be strictly counted;
for, besides the twenty, there were all possible gradations between a
short length of a rhizome just perceptibly swollen and one so much
swollen that it might be doubtfully called a tuber. When well
developed, they are oval and symmetrical, more so than appears in the
figure. The largest which I saw was 1 inch (25.4 mm.) in length and .45
inch (11.43 mm.) in breadth. They commonly lie near the surface, but
some are buried at the depth of 2 inches. The buried ones are dirty
white, but those partly exposed to the light become greenish from the
development, of chlorophyll in their superficial cells. They terminate
in a rhizome, but this sometimes decays and drops off . They do not
contain any air, and they sink in water; their surfaces are covered
with the usual papillae. The bundle of vessels which runs up each
rhizome, as soon as it enters the tuber, separates into three distinct
bundles, which reunite at the opposite end. A rather thick slice of a
tuber is almost as translucent as glass, and is seen to consist of
large angular cells, full of water and not containing starch or any
other solid matter. Some slices were left in alcohol for several days,
but only a few extremely minute granules of matter were precipitated on
the walls of the cells; and these were much smaller and fewer than
those precipitated on the cell-walls of the rhizomes and bladders. We
may therefore con- [page 440] clude that the tuber do not serve as
reservoirs for food, but for water during the dry season to which the
plant is probably exposed. The many little bladders filled with water
would aid towards the same end.

To test the correctness of this view, a small plant, growing in light
peaty earth in a pot (only 4 1/2 by 4 1/2 inches outside measure) was
copiously watered, and then kept without a drop of water in the
hothouse. Two of the upper tubers were beforehand uncovered and
measured, and then loosely covered up again. In a fortnight’s time the
earth in the pot appeared extremely dry; but not until the thirty-fifth
day were the leaves in the least affected; they then became slightly
reflexed, though still soft and green. This plant, which bore only ten
tubers, would no doubt have resisted the drought for even a longer
time, had I not previously removed three of the tubers and cut off
several long rhizomes. When, on the thirty-fifth day, the earth in the
pot was turned out, it appeared as dry as the dust on a road. All the
tubers had their surfaces much wrinkled, instead of being smooth and
tense. They had all shrunk, but I cannot say accurately how much; for
as they were at first symmetrically oval, I measured only their length
and thickness; but they contracted in a transverse line much more in
one direction than in another, so as to become greatly flattened. One
of the two tubers which had been measured was now three-fourths of its
original length, and two-thirds of its original thickness in the
direction in which it had been measured, but in another direction only
one- third of its former thickness. The other tuber was one-fourth
shorter, one-eighth less thick in the direction in which it had been
measured, and only half as thick in another direction.

A slice was cut from one of these shrivelled tubers [page 441] and
examined. The cells still contained much water and no air, but they
were more rounded or less angular than before, and their walls not
nearly so straight; it was therefore clear that the cells had
contracted. The tubers, as long as they remain alive, have a strong
attraction for water; the shrivelled one, from which a slice had been
cut, was left in water for 22 hrs. 30 m., and its surface became as
smooth and tense as it originally was. On the other hand, a shrivelled
tuber, which by some accident had been separated from its rhizome, and
which appeared dead, did not swell in the least, though left for
several days in water.

With many kinds of plants, tubers, bulbs, &c. no doubt serve in part as
reservoirs for water, but I know of no case, besides the present one,
of such organs having been developed solely for this purpose. Prof.
Oliver informs me that two or three species of Utricularia are provided
with these appendages; and the group containing them has in consequence
received the name of orchidioides. All the other species of
Utricularia, as well as of certain closely related genera, are either
aquatic or marsh plants; therefore, on the principle of nearly allied
plants generally having a similar constitution, a never failing supply
of water would probably be of great importance to our present species.
We can thus understand the meaning of the development of its tubers,
and of their number on the same plant, amounting in one instance to at
least twenty.

UTRICULARIA NELUMBIFOLIA, AMETHYSTINA, GRIFFITHII, CAERULEA,
ORBICULATA, MULTICAULIS.


As I wished to ascertain whether the bladders on the rhizomes of other
species of Utricularia, and of the [page 442] species of certain
closely allied genera, had the same essential structure as those of
Utricularia montana, and whether they captured prey, I asked Prof.
Oliver to send me fragments from the herbarium at Kew. He kindly
selected some of the most distinct forms, having entire leaves, and
believed to inhabit marshy ground or water. My son Francis Darwin,
examined them, and has given me the following observations; but it
should be borne in mind that it is extremely difficult to make out the
structure of such minute and delicate objects after they have been
dried and pressed.*

Utricularia nelumbifolia (Organ Mountains, Brazil).—The habitat of this
species is remarkable. According to its discoverer, Mr. Gardner,** it
is aquatic, but “is only to be found growing in the water which
collects in the bottom of the leaves of a large Tillandsia, that
inhabits abundantly an arid rocky part of the mountain, at an elevation
of about 5000 feet above the level of the sea. Besides the ordinary
method by seed, it propagates itself by runners, which it throws out
from the base of the flower-stem; this runner is always found directing
itself towards the nearest Tillandsia, when it inserts its point into
the water and gives origin to a new plant, which in its turn sends out
another shoot. In this manner I have seen not less than six plants
united.” The bladders resemble those of Utricularia montana in all
essential respects, even to the presence of a few minute two-armed
glands on the valve. Within one bladder there was the remnant of the
abdomen of some larva or crustacean of large size,

* Prof. Oliver has given (‘Proc. Linn. Soc.’ vol. iv. p. 169) figures
of the bladders of two South American species, namely Utricularia
Jamesoniana and peltata; but he does not appear to have paid particular
attention to these organs.


** ‘Travels in the Interior of Brazil, 1836-41,’ p. 527. [page 443]


having a brush of long sharp bristles at the apex. Other bladders
included fragments of articulate animals, and many of them contained
broken pieces of a curious organism, the nature of which was not
recognised by anyone to whom it was shown.

Utricularia amethystina (Guiana).—This species has small entire leaves,
and is apparently a marsh plant; but it must grow in places where
crustaceans exist, for there were two small species within one of the
bladders. The bladders are nearly of the same shape as those of
Utricularia montana, and are covered outside with the usual papillae;
but they differ remarkably in the antennæ being reduced to two short
points, united by a membrane hollowed out in the middle. This membrane
is covered with innumerable oblong glands supported on long footstalks;
most of which are arranged in two rows converging towards the valve.
Some, however, are seated on the margins of the membrane; and the short
ventral surface of the bladder, between the petiole and valve, is
thickly covered with glands. Most of the heads had fallen off, and the
footstalks alone remained; so that the ventral surface and the orifice,
when viewed under a weak power, appeared as if clothed with fine
bristles. The valve is narrow, and bears a few almost sessile glands.
The collar against which the edge shuts is yellowish, and presents the
usual structure. From the large number of glands on the ventral surface
and round the orifice, it is probable that this species lives in very
foul water, from which it absorbs matter, as well as from its captured
and decaying prey.

Utricularia griffithii (Malay and Borneo).—The bladders are transparent
and minute; one which was measured being only 28/1000 of an inch (.711
mm.) in diameter. The antennæ are of moderate length, and [page 444]
project straight forward; they are united for a short space at their
bases by a membrane; and they bear a moderate number of bristles or
hairs, not simple as heretofore, but surmounted by glands. The bladders
also differ remarkably from those of the previous species, as within
there are no quadrifid, only bifid, processes. In one bladder there was
a minute aquatic larva; in another the remains of some articulate
animal; and in most of them grains of sand.

Utricularia caerulea (India).—The bladders resemble those of the last
species, both in the general character of the antennæ and in the
processes within being exclusively bifid. They contained remnants of
entomostracan crustaceans.

Utricularia orbiculata (India).—The orbicular leaves and the stems
bearing the bladders apparently float in water. The bladders do not
differ much from those of the two last species. The antennæ, which are
united for a short distance at their bases, bear on their outer
surfaces and summits numerous, long, multicellular hairs, surmounted by
glands. The processes within the bladders are quadrifid, with the four
diverging arms of equal length. The prey which they had captured
consisted of entomostracan crustaceans.

Utricularia multicaulis (Sikkim, India, 7000 to 11,000 feet).—The
bladders, attached to rhizomes, are remarkable from the structure of
the antennæ. These are broad, flattened, and of large size; they bear
on their margins multicellular hairs, surmounted by glands. Their bases
are united into a single, rather narrow pedicel, and they thus appear
like a great digitate expansion at one end of the bladder. Internally
the quadrifid processes have divergent arms of equal length. The
bladders contained remnants of articulate animals. [page 445]

POLYPOMPHOLYX.


This genus, which is confined to Western Australia, is characterised by
having a “quadripartite calyx.” In other respects, as Prof. Oliver
remarks,* “it is quite a Utricularia.”

Polypompholyx multifida.—The bladders are attached in whorls round the
summits of stiff stalks. The two antennæ are represented by a minute
membranous fork, the basal part of which forms a sort of hood over the
orifice. This hood expands into two wings on each side of the bladder.
A third wing or crest appears to be formed by the extension of the
dorsal surface of the petiole; but the structure of these three wings
could not be clearly made out, owing to the state of the specimens. The
inner surface of the hood is lined with long simple hairs, containing
aggregated matter, like that within the quadrifid processes of the
previously described species when in contact with decayed animals.
These hairs appear therefore to serve as absorbents. A valve was seen,
but its structure could not be determined. On the collar round the
valve there are in the place of glands numerous one-celled papillae,
having very short footstalks. The quadrifid processes have divergent
arms of equal length. Remains of entomostracan crustaceans were found
within the bladders.

Polypompholyx tenella.—The bladders are smaller than those of the last
species, but have the same general structure. They were full of dbris,
apparently organic, but no remains of articulate animals could be
distinguished.

* ‘Proc. Linn. Soc.’ vol. iv. p. 171. [page 446]


GENLISEA.


This remarkable genus is technically distinguished from Utricularia, as
I hear from Prof. Oliver, by having a five-partite calyx. Species are
found in several parts of the world, and are said to be “herbae annuae
paludosae.”

Genlisea ornata (Brazil).—This species has been described and figured
by Dr. Warming,* who states that it bears two kinds of leaves, called
by him spathulate and utriculiferous. The latter include cavities; and
as these differ much from the bladders of the foregoing species, it
will be convenient to speak of them as utricles. The accompanying
figure (fig. 29) of one of the utriculiferous leaves, about thrice
enlarged, will illustrate the following description by my son, which
agrees in all essential points with that given by Dr. Warming. The
utricle (b) is formed by a slight enlargement of the narrow blade of
the leaf. A hollow neck (n), no less than fifteen times as long as the
utricle itself, forms a passage from the transverse slit-like orifice
(o) into the cavity of the utricle. A utricle which measured 1/36 of an
inch (.705 mm.,) in its longer diameter had a neck 15/36 (10.583 mm.)
in length, and 1/100 of an inch (.254 mm.) in breadth. On each side of
the orifice there is a long spiral arm or tube (a); the structure of
which will be best understood by the following illustration. Take a
narrow ribbon and wind it spirally round a thin cylinder, so that the
edges come into contact along its whole length; then pinch up the two
edges so as to form a little crest, which will of course wind spirally

* “Bidrag til Kundskaben om Lentibulariaceae,” Copenhagen 1874. [page
447]


round the cylinder like a thread round a screw. If the cylinder is now
removed, we shall have a tube like one of the spiral arms. The two
projecting edges are not actually united, and a needle can be pushed in
easily between them. They are indeed in many places a little separated,
forming narrow entrances into the tube; but this may be the result of
the drying of the specimens. The lamina of which the tube is formed
seems to be a lateral prolongation of the lip of the orifice; and the
spiral line between the two projecting edges is continuous with the
corner of the orifice. If a fine bristle is pushed down one of the
arms, it passes into the top of the hollow neck. Whether the arms are
open or closed at their extremities could not be determined, as all the
specimens were broken; nor does it appear that Dr. Warming ascertained
this point.

FIG. 29. (Genlisea ornata.) Utriculiferous leaf; enlarged about three
times. l Upper part of lamina of leaf. b Utricle or bladder. n Neck of
utricle. o Orifice. a Spirally wound arms, with their ends broken off.

So much for the external structure. Internally the lower part of the
utricle is covered with spherical papillae, formed of four cells
(sometimes eight according to Dr. Warming), which evidently answer to
the quadrifid processes within the bladders of Utricularia. [page 448]
These papillae extend a little way up the dorsal and ventral surfaces
of the utricle; and a few, according to Warming, may be found in the
upper part. This upper region is covered by many transverse rows, one
above the other, of short, closely approximate hairs, pointing
downwards. These hairs have broad bases, and their tips are formed by a
separate cell. They are absent in the lower part of the utricle where
the papillae abound.

FIG. 30. (Genlisea ornata.) Portion of inside of neck leading into the
utricle, greatly enlarged, showing the downward pointed bristles, and
small quadrifid cells or processes.

The neck is likewise lined throughout its whole length with transverse
rows of long, thin, transparent hairs, having broad bulbous (fig. 30)
bases, with similarly constructed sharp points. They arise from little
projecting ridges, formed of rectangular epidermic cells. The hairs
vary a little in length, but their points generally extend down to the
row next below; so that if the neck is split open and laid flat, the
inner surface resembles a paper of pins,—the hairs representing the
pins, and the little transverse ridges representing the folds of paper
through which the pins are thrust. These rows of hairs are indicated in
the previous figure (29) by numerous transverse lines crossing the
neck. The inside of the neck is [page 449] also studded with papillae;
those in the lower part are spherical and formed of four cells, as in
the lower part of the utricle; those in the upper part are formed of
two cells, which are much elongated downwards beneath their points of
attachment. These two-celled papillae apparently correspond with the
bifid process in the upper part of the bladders of Utricularia. The
narrow transverse orifice (o, fig. 29) is situated between the bases of
the two spiral arms. No valve could be detected here, nor was any such
structure seen by Dr. Warming. The lips of the orifice are armed with
many short, thick, sharply pointed, somewhat incurved hairs or teeth.

The two projecting edges of the spirally wound lamina, forming the
arms, are provided with short incurved hairs or teeth, exactly like
those on the lips. These project inwards at right angles to the spiral
line of junction between the two edges. The inner surface of the lamina
supports two-celled, elongated papillae, resembling those in the upper
part of the neck, but differing slightly from them, according to
Warming, in their footstalks being formed by prolongations of large
epidermic cells; whereas the papillae within the neck rest on small
cells sunk amidst the larger ones. These spiral arms form a conspicuous
difference between the present genus and Utricularia.

Lastly, there is a bundle of spiral vessels which, running up the lower
part of the linear leaf, divides close beneath the utricle. One branch
extends up the dorsal and the other up the ventral side of both the
utricle and neck. Of these two branches, one enters one spiral arm, and
the other branch the other arm.

The utricles contained much dbris or dirty matter, which seemed
organic, though no distinct organisms [page 450] could be recognised.
It is, indeed, scarcely possible that any object could enter the small
orifice and pass down the long narrow neck, except a living creature.
Within the necks, however, of some specimens, a worm with retracted
horny jaws, the abdomen of some articulate animal, and specks of dirt,
probably the remnants of other minute creatures, were found. Many of
the papillae within both the utricles and necks were discoloured, as if
they had absorbed matter.

From this description it is sufficiently obvious how Genlisea secures
its prey. Small animals entering the narrow orifice—but what induces
them to enter is not known any more than in the case of
Utricularia—would find their egress rendered difficult by the sharp
incurved hairs on the lips, and as soon as they passed some way down
the neck, it would be scarcely possible for them to return, owing to
the many transverse rows of long, straight, downward pointing hairs,
together with the ridges from which these project. Such creatures
would, therefore, perish either within the neck or utricle; and the
quadrifid and bifid papillae would absorb matter from their decayed
remains. The transverse rows of hairs are so numerous that they seem
superfluous merely for the sake of preventing the escape of prey, and
as they are thin and delicate, they probably serve as additional
absorbents, in the same manner as the flexible bristles on the infolded
margins of the leaves of Aldrovanda. The spiral arms no doubt act as
accessory traps. Until fresh leaves are examined, it cannot be told
whether the line of junction of the spirally wound lamina is a little
open along its whole course, or only in parts, but a small creature
which forced its way into the tube at any point, would be prevented
from escaping by the incurved hairs, and would find an open path down
[page 451] the tube into the neck, and so into the utricle. If the
creature perished within the spiral arms, its decaying remains would be
absorbed and utilised by the bifid papillae. We thus see that animals
are captured by Genlisea, not by means of an elastic valve, as with the
foregoing species, but by a contrivance resembling an eel-trap, though
more complex.

Genlisea africana (South Africa).—Fragments of the utriculiferous
leaves of this species exhibited the same structure as those of
Genlisea ornata. A nearly perfect Acarus was found within the utricle
or neck of one leaf, but in which of the two was not recorded.

Genlisea aurea (Brazil).—A fragment of the neck of a utricle was lined
with transverse rows of hairs, and was furnished with elongated
papillae, exactly like those within the neck of Genlisea ornata. It is
probable, therefore, that the whole utricle is similarly constructed.

Genlisea filiformis (Bahia, Brazil).—Many leaves were examined and none
were found provided with utricles, whereas such leaves were found
without difficulty in the three previous species. On the other hand,
the rhizomes bear bladders resembling in essential character those on
the rhizomes of Utricularia. These bladders are transparent, and very
small, viz. Only 1/100 of an inch (.254 mm.) in length. The antennæ are
not united at their bases, and apparently bear some long hairs. On the
outside of the bladders there are only a few papillae, and internally
very few quadrifid processes. These latter, however, are of unusually
large size, relatively to the bladder, with the four divergent arms of
equal length. No prey could be seen within these minute bladders. As
the rhizomes of this species were furnished with bladders, those of
Genlisea africana, ornata, and aurea were carefully [page 452]
examined, but none could be found. What are we to infer from these
facts? Did the three species just named, like their close allies, the
several species of Utricularia, aboriginally possess bladders on their
rhizomes, which they afterwards lost, acquiring in their place
utriculiferous leaves? In support of this view it may be urged that the
bladders of Genlisea filiformis appear from their small size and from
the fewness of their quadrifid processes to be tending towards
abortion; but why has not this species acquired utriculiferous leaves,
like its congeners?




CONCLUSION.


It has now been shown that many species of Utricularia and of two
closely allied genera, inhabiting the most distant parts of the
world—Europe, Africa, India, the Malay Archipelago, Australia, North
and South America—are admirably adapted for capturing by two methods
small aquatic or terrestrial animals, and that they absorb the products
of their decay.

Ordinary plants of the higher classes procure the requisite inorganic
elements from the soil by means of their roots, and absorb carbonic
acid from the atmosphere by means of their leaves and stems. But we
have seen in a previous part of this work that there is a class of
plants which digest and afterwards absorb animal matter, namely, all
the Droseraceae, Pinguicula, and, as discovered by Dr. Hooker,
Nepenthes, and to this class other species will almost certainly soon
be added. These plants can dissolve matter out of certain vegetable
substances, such as pollen, seeds, and bits of leaves. No doubt their
glands likewise absorb the salts of ammonia brought to them by the
rain. It has also been shown that some other plants can absorb ammonia
by [page 453] their glandular hairs; and these will profit by that
brought to them by the rain. There is a second class of plants which,
as we have just seen, cannot digest, but absorb the products of the
decay of the animals which they capture, namely, Utricularia and its
close allies; and from the excellent observations of Dr. Mellichamp and
Dr. Canby, there can scarcely be a doubt that Sarracenia and
Darlingtonia may be added to this class, though the fact can hardly be
considered as yet fully proved. There is a third class of plants which
feed, as is now generally admitted, on the products of the decay of
vegetable matter, such as the bird’s-nest orchis (Neottia), &c. Lastly,
there is the well-known fourth class of parasites (such as the
mistletoe), which are nourished by the juices of living plants. Most,
however, of the plants belonging to these four classes obtain part of
their carbon, like ordinary species, from the atmosphere. Such are the
diversified means, as far as at present known, by which higher plants
gain their subsistence.




INDEX.


A.

Absorption by Dionaea, 295
— by Drosera, 17
— by Drosophyllum, 337
— by Pinguicula, 381
— by glandular hairs, 344
— by glands of Utricularia, 416, 421
— by quadrifids of Utricularia, 413, 421
— by Utricularia montana, 437

Acid, nature of, in digestive secretion of Drosera, 88 — present in
digestive fluid of various species of Drosera, Dionaea, Drosophyllum,
and Pinguicula, 278, 301, 339, 381

Acids, various, action of, on Drosera, 188 — of the acetic series
replacing hydrochloric in digestion, 89 —, arsenious and chromic,
action on Drosera, 185 —, diluted, inducing negative osmose, 197

Adder’s poison, action on Drosera, 206

Aggregation of protoplasm in Drosera, 38 — in Drosera induced by salts
of ammonia, 43 — — caused by small doses of carbonate of ammonia, 145 —
of protoplasm in Drosera, a reflex action, 242 — — in various species
of Drosera, 278 — — in Dionaea, 290, 300

Aggregation of protoplasm in Drosophyllum, 337, 339 — — in Pinguicula,
370, 389 — — in Utricularia, 411, 415, 429, 430, 436

Albumen, digested by Drosera, 92 —, liquid, action on Drosera, 79

Alcohol, diluted, action of, on Drosera, 78, 216

Aldrovanda vesiculosa, 321 —, absorption and digestion by, 325 —,
varieties of, 329

Algae, aggregation in fronds of, 65

Alkalies, arrest digestive process in Drosera, 94

Aluminium, salts of, action on Drosera, 184

Ammonia, amount of, in rain water, 172 —, carbonate, action on heated
leaves of Drosera, 69 —, —, smallness of doses causing aggregation in
Drosera, 145 —, —, its action on Drosera, 141 —, —, vapour of, absorbed
by glands of Drosera, 142 —, —, smallness of doses causing inflection
in Drosera, 145, 168 —, phosphate, smallness of doses causing
inflection in Drosera, 153, 168 —, —, size of particles affecting
Drosera, 173 —, nitrate, smallness of doses causing inflection in
Drosera, 148, 168 —, salts of, action on Drosera, 136

Ammonia, salts of, their action affected by previous immersion in water
and various solutions, 213 —, —, induce aggregation in Drosera, 43 —,
various salts of, causing inflection in Drosera, 166

Antimony, tartrate, action on Drosera, 185

Areolar tissue, its digestion by Drosera, 102

Arsenious acid, action on Drosera, 185

Atropine, action on Drosera, 204


B.

Barium, salts of, action on Drosera, 183

Bases of salts, preponderant action of, on Drosera, 186

Basis, fibrous, of bone, its digestion by Drosera, 108

Belladonna, extract of, action on Drosera, 84

Bennett, Mr. A.W., on Drosera, 2 —, coats of pollen-grains not digested
by insects, 117

Binz, on action of quinine on white blood-corpuscles, 201 —, on
poisonous action of quinine on low organisms, 202

Bone, its digestion by Drosera, 105

Brunton, Lauder, on digestion of gelatine, 111 —, on the composition of
casein, 115 —, on the digestion of urea, 124 —, — of chlorophyll, 126
—, — of pepsin, 124

Byblis, 343


C.

Cabbage, decoction of, action on Drosera, 83

Cadmium chloride, action on Drosera, 183

Caesium, chloride of, action on Drosera, 181

Calcium, salts of, action on Drosera, 182

Camphor, action on Drosera, 209

Canby, Dr., on Dionaea, 301, 310, 313 —, on Drosera filiformis, 281

Caraway, oil of, action on Drosera, 211

Carbonic acid, action on Drosera, 221 —, delays aggregation in Drosera,
59

Cartilage, its digestion by Drosera, 103

Casein, its digestion by Drosera, 114

Cellulose, not digested by Drosera, 125

Chalk, precipitated, causing inflection of Drosera, 32

Cheese, its digestion by Drosera, 116

Chitine, not digested by Drosera, 124

Chloroform, effects of, on Drosera, 217 —, —, on Dionaea, 304

Chlorophyll, grains of, in living plants, digested by Drosera, 126 —,
pure, not digested by Drosera, 125

Chondrin, its digestion by Drosera, 112

Chromic acid, action on Drosera, 185

Cloves, oil of, action on Drosera, 212

Cobalt chloride, action on Drosera, 186

Cobra poison, action on Drosera, 206

Cohn, Prof., on Aldrovanda, 321 —, on contractile tissues in plants,
364 —, on movements of stamens of Compositae, 256 —, on Utricularia,
395

Colchicine, action on Drosera, 204

Copper chloride, action on Drosera, 185

Crystallin, its digestion by Drosera, 120

Curare, action on Drosera, 204

Curtis, Dr., on Dionaea, 301


D.

Darwin, Francis, on the effect of an induced galvanic current on
Drosera, 37 —, on the digestion of grains of chlorophyll, 126 —, on
Utricularia, 442

Delpino, on Aldrovanda, 321 —, on Utricularia, 395

Dentine, its digestion by Drosera, 106

Digestion of various substances by Dionaea, 301 — — by Drosera, 85 — —
by Drosophyllum, 339 — — by Pinguicula, 381 —, origin of power of, 361

Digitaline, action on Drosera, 203

Dionaea muscipula, small size of roots, 286 —, structure of leaves, 287
—, sensitiveness of filaments, 289 —, absorption by, 295 —, secretion
by, 295 —, digestion by, 301 —, effects on, of chloroform, 304 —,
manner of capturing insects, 305 —, transmission of motor impulse, 313
—, re-expansion of lobes, 318

Direction of inflected tentacles of Drosera, 243

Dohrn, Dr., on rhizocephalous crustaceans, 357

Donders, Prof., small amount of atropine affecting the iris of the dog,
172

Dragonfly caught by Drosera, 2

Drosera anglica, 278 — binata, vel dichotoma, 281 — capensis, 279 —
filiformis, 281 — heterophylla, 284 — intermedia, 279

Drosera rotundifolia, structure of leaves, 4 —, effects on, of
nitrogenous fluids, 76 Drosera rotundifolia, effects of heat on, 66 —,
its power of digestion, 85 —, backs of leaves not sensitive, 231 —,
transmission of motor impulse, 234 —, general summary, 262 —
spathulata, 280

Droseraceae, concluding remarks on, 355 —, their sensitiveness compared
with that of animals, 366

Drosophyllum, structure of leaves, 333 —, secretion by, 334 —,
absorption by, 337 —, digestion by, 339


E.

Enamel, its digestion by Drosera, 106

Erica tetralix, glandular hairs of, 351

Ether, effects of, on Drosera, 219 —, —, on Dionaea, 304

Euphorbia, process of aggregation in roots of, 63

Exosmose from backs of leaves of Drosera, 231


F.

Fat not digested by Drosera, 126

Fayrer, Dr., on the nature of cobra poison, 206 —, on the action of
cobra poison on animal protoplasm, 208 —, on cobra poison paralysing
nerve centres, 224

Ferment, nature of, in secretion of Drosera, 94, 97

Fibrin, its digestion by Drosera, 100

Fibro-cartilage, its digestion by Drosera, 104

Fibro-elastic tissue, not digested by Drosera, 122

Fibrous basis of bone, its digestion by Drosera, 108

Fluids, nitrogenous, effects of, on Drosera, 76

Fournier, on acids causing movements in stamens of Berberis, 196

Frankland, Prof., on nature of acid in secretion of Drosera, 88


G.

Galvanism, current of, causing inflection of Drosera, 37 —, effects of,
on Dionaea, 318

Gardner, Mr., on Utricularia nelumbifolia, 442

Gelatin, impure, action on Drosera, 80 —, pure, its digestion by
Drosera, 110

Genlisea africana, 451 — filiformis, 451

Genlisea ornata, structure of, 446 —, manner of capturing prey, 450

Glandular hairs, absorption by, 344 —, summary on, 353

Globulin, its digestion by Drosera, 120

Gluten, its digestion by Drosera, 117

Glycerine, inducing aggregation in Drosera, 52 —, action on Drosera,
212

Gold chloride, action on Drosera, 184

Gorup-Besanez on the presence of a solvent in seeds of the vetch, 362

Grass, decoction of, action on Drosera, 84

Gray, Asa, on the Droseraceae, 2

Groenland, on Drosera, 1, 5

Gum, action of, on Drosera, 77

Gun-cotton, not digested by Drosera, 125


H.

Haematin, its digestion by Drosera, 121

Hairs, glandular, absorption by, 344 —, —, summary on, 353

Heat, inducing aggregation in Drosera, 53 —, effect of, on Drosera, 66
—, —, on Dionaea, 294, 319

Heckel, on state of stamens of Berberis after excitement, 43

Hofmeister, on pressure arresting movements of protoplasm, 61

Holland, Mr., on Utricularia, 395

Hooker, Dr., on carnivorous plants, 2 —, on power of digestion by
Nepenthes, 97 —, history of observations on Dionaea, 286

Hydrocyanic acid, effects of, on Dionaea, 305

Hyoscyamus, action on Drosera, 84, 206


I.

Iron chloride, action on Drosera, 185

Isinglass, solution of, action on Drosera, 80


J.

Johnson, Dr., on movement of flower-stems of Pinguicula, 381


K.

Klein, Dr., on microscopic character of half digested bone, 106 —, on
state of half digested fibro-cartilage, 104 —, on size of micrococci,
173

Knight, Mr., on feeding Dionaea, 301

Kossmann, Dr., on rhizocephalous crustaceans, 357


L.

Lead chloride, action on Drosera, 184

Leaves of Drosera, backs of, not sensitive, 231

Legumin, its digestion by Drosera, 116

Lemna, aggregation in leaves of, 64

Lime, carbonate of, precipitated, causing inflection of Drosera, 32 —,
phosphate of, its action on Drosera, 109

Lithium, salts of, action on Drosera, 181


M.

Magnesium, salts of, action on Drosera, 182

Manganese chloride, action on Drosera, 185

Marshall, Mr. W., on Pinguicula, 369

Means of movement in Dionaea, 313 — in Drosera, 254

Meat, infusion of, causing aggregation in Drosera, 51 —, —, action on
Drosera, 79 —, its digestion by Drosera, 98

Mercury perchloride, action on Drosera, 183

Milk, inducing aggregation in Drosera, 51 —, action on Drosera, 79 —,
its digestion by Drosera, 113

Mirabilis longiflora, glandular hairs of, 352

Moggridge, Traherne, on acids injuring seeds, 128

Moore, Dr., on Pinguicula, 390

Morphia acetate, action on Drosera, 205

Motor impulse in Drosera, 234, 258 — in Dionaea, 313

Movement, origin of power of, 363

Movements of leaves of Pinguicula, 371 — of tentacles of Drosera, means
of, 254 — of Dionaea, means of, 313

Mucin, not digested by Drosera, 122

Mucus, action on Drosera, 80

Müller, Fritz, on rhizocephalous crustaceans, 357


N.

Nepenthes, its power of digestion, 97

Nickel chloride, action on Drosera, 186

Nicotiana tabacum, glandular hairs of, 352

Nicotine, action on Drosera, 203

Nitric ether, action on Drosera, 220

Nitschke, Dr., references to his papers on Drosera, 1 —, on
sensitiveness of backs of leaves of Drosera, 231 —, on direction of
inflected tentacles in Drosera, 244 —, on Aldrovanda, 322

Nourishment, various means of, by plants, 452

Nuttall, Dr., on re-expansion of Dionaea, 318


O.

Odour of pepsin, emitted from leaves of Drosera, 88

Oil, olive, action of, on Drosera, 78, 126

Oliver, Prof., on Utricularia, 432, 441-446


P.

Papaw, juice of, hastening putrefaction, 411

Particles, minute size of, causing inflection in Drosera, 27, 32

Peas, decoction of, action on Drosera, 82

Pelargonium zonale, glandular hairs of, 350

Pepsin, odour of, emitted from Drosera leaves, 88 —, not digested by
Drosera, 123 —, its secretion by animals excited only after absorption,
129

Peptogenes, 129

Pinguicula grandiflora, 390 — lusitanica, 391

Pinguicula vulgaris, structure of leaves and roots, 368 —, number of
insects caught by, 369 —, power of movement, 371 —, secretion and
absorption by, 381 —, digestion by, 381 —, effects of secretion on
living seeds, 390

Platinum chloride, action on Drosera, 186

Poison of cobra and adder, their action on Drosera, 206

Pollen, its digestion by Drosera, 117

Polypompholyx, structure of, 445

Potassium, salts of, inducing aggregation in Drosera, 50 —, —, action
on Drosera, 179 — phosphate, not decomposed by Drosera, 180, 187

Price, Mr. John, on Utricularia, 429

Primula sinensis, glandular hairs of, 348 —, number of glandular hairs
of, 355

Protoplasm, aggregation of, in Drosera, 38 —, —, in Drosera, caused by
small doses of carbonate of ammonia, 145 —, —, in Drosera, a reflex
action, 242 — aggregated, re-dissolution of, 53 —, aggregation of, in
various species of Drosera, 278 —, —, in Dionaea, 290, 300 —, —, in
Drosophyllum, 337, 339 —, —, in Pinguicula, 370, 389 —, —, in
Utricularia, 411, 415, 429, 430, 436


Q.

Quinine, salts of, action on Drosera, 201


R.

Rain-water, amount of ammonia in, 172

Ralfs, Mr., on Pinguicula, 390

Ransom, Dr., action of poisons on the yolk of eggs, 225

Re-expansion of headless tentacles of Drosera, 229 — of tentacles of
Drosera, 260 — of Dionaea, 318

Roots of Drosera, 18 — of Drosera, process of aggregation in, 63 — of
Drosera, absorb carbonate of ammonia, 141 — of Dionaea, 286 — of
Drosophyllum, 332 — of Pinguicula, 369

Roridula, 342

Rubidium chloride, action on Drosera, 181


S.

Sachs, Prof., effects of heat on protoplasm, 66, 70 —, on the
dissolution of proteid compounds in the tissues of plants, 362

Saliva, action on Drosera, 80

Salts and acids, various, effects of, on subsequent action of ammonia,
214

Sanderson, Burdon, on coagulation of albumen from heat, 74 —, on acids
replacing hydrochloric in digestion, 89 —, on the digestion of fibrous
basis of bone, 108 —, — of gluten, 118 —, — of globulin, 120 —, — of
chlorophyll, 126 —, on different effect of sodium and potassium on
animals, 187 —, on electric currents in Dionaea, 318

Saxifraga umbrosa, glandular hairs of, 345

Schiff, on hydrochloric acid dissolving coagulated albumen, 86 —, on
manner of digestion of albumen, 93 —, on changes in meat during
digestion, 99 —, on the coagulation of milk, 114 —, on the digestion of
casein, 116 —, — of mucus, 123 —, on peptogenes, 129

Schloesing, on absorption of nitrogen by Nicotiana, 352

Scott, Mr., on Drosera, 1

Secretion of Drosera, general account of, 13 — —, its antiseptic power,
15 — —, becomes acid from excitement, 86 — —, nature of its ferment,
94, 97 — by Dionaea, 295 — by Drosophyllum, 335 — by Pinguicula, 381

Seeds, living, acted on by Drosera, 127 —, —, acted on by Pinguicula,
385, 390

Sensitiveness, localisation of, in Drosera, 229 — of Dionaea, 289 — of
Pinguicula, 371

Silver nitrate, action on Drosera, 181

Sodium, salts of, action on Drosera, 176 —, —, inducing aggregation in
Drosera, 50

Sondera heterophylla, 284

Sorby, Mr., on colouring matter of Drosera, 5

Spectroscope, its power compared with that of Drosera, 170

Starch, action of, on Drosera, 78, 126

Stein, on Aldrovanda, 321

Strontium, salts of, action on Drosera, 183

Strychnine, salts of, action on Drosera, 199

Sugar, solution of, action of, on Drosera, 78 —, —, inducing
aggregation in Drosera, 51

Sulphuric ether, action on Drosera, 219 —, — on Dionaea, 304

Syntonin, its action on Drosera, 102


T.

Tait, Mr., on Drosophyllum, 332

Taylor, Alfred, on the detection of minute doses of poisons, 170

Tea, infusion of, action on Drosera, 78

Tentacles of Drosera, move when glands cut of, 36, 229 —, inflection,
direction of, 243 —, means of movement, 254 —, re-expansion of, 260

Theine, action on Drosera, 204

Tin chloride, action on Drosera, 185

Tissue, areolar, its digestion by Drosera, 102 —, fibro-elastic, not
digested by Drosera, 122

Tissues through which impulse is transmitted in Drosera, 247 — — in
Dionaea, 313

Touches repeated, causing inflection in Drosera, 34

Transmission of motor impulse in Drosera, 234 — — in Dionaea, 313

Traube, Dr., on artificial cells, 216

Treat, Mrs., on Drosera filiformis, 281 —, on Dionaea, 311 —, on
Utricularia, 408, 430

Trcul, on Drosera, 1, 5

Tubers of Utricularia montana, 439

Turpentine, action on Drosera, 212


U.

Urea, not digested by Drosera, 124

Urine, action on Drosera, 79

Utricularia clandestina, 430 — minor, 429

Utricularia montana, structure of bladders, 431 —, animals caught by,
435 —, absorption by, 437 —, tubers of, serving as reservoirs, 439

Utricularia neglecta, structure of bladders, 397 —, animals caught by,
405 —, absorption by, 413 —, summary on absorption, 421 —, development
of bladders, 424

Utricularia, various species of, 441

Utricularia vulgaris, 428


V.

Veratrine, action on Drosera, 204

Vessels in leaves of Drosera, 247 — of Dionaea, 314

Vogel, on effects of camphor on plants, 209


W.

Warming, Dr., on Drosera, 2, 6 —, on roots of Utricularia, 397 —, on
trichomes, 359 —, on Genlisea, 446 —, on parenchymatous cells in
tentacles of Drosera, 252

Water, drops of, not causing inflection in Drosera, 35 —, its power in
causing aggregation in Drosera, 52 —, its power in causing inflection
in Drosera, 139 — and various solutions, effects of, on subsequent
action of ammonia, 213

Wilkinson, Rev., on Utricularia, 398


Z.

Ziegler, his statements with respect to Drosera, 23 —, experiments by
cutting vessels of Drosera, 249

Zinc chloride, action on Drosera, 184






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