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diff --git a/5765-0.txt b/5765-0.txt new file mode 100644 index 0000000..463f84c --- /dev/null +++ b/5765-0.txt @@ -0,0 +1,16336 @@ +The Project Gutenberg eBook of Insectivorous Plants, by Charles Darwin + +This eBook is for the use of anyone anywhere in the United States and +most other parts of the world at no cost and with almost no restrictions +whatsoever. You may copy it, give it away or re-use it under the terms +of the Project Gutenberg License included with this eBook or online at +www.gutenberg.org. If you are not located in the United States, you +will have to check the laws of the country where you are located before +using this eBook. + +Title: Insectivorous Plants + +Author: Charles Darwin + +Release Date: August 31, 2002 [eBook #5765] +[Most recently updated: December 28, 2021] + +Language: English + +Character set encoding: UTF-8 + +Produced by: 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 + + + + +*** END OF THE PROJECT GUTENBERG EBOOK INSECTIVOROUS PLANTS *** + +Updated editions will replace the previous one--the old editions will +be renamed. + +Creating the works from print editions not protected by U.S. copyright +law means that no one owns a United States copyright in these works, +so the Foundation (and you!) can copy and distribute it in the +United States without permission and without paying copyright +royalties. 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