Insectivorous Plants

nearer together than before. If we suppose the whole upper surface of the lobe, which was Vo'Vo of an inch in breadth, to have contracted in the same proportion, the total contraction will have amounted to about T I g 0 or -JIT °f an incn ('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 Sander- son* 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 oc- curred 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 £ut off close to their bases ; and the three

t Nuttall, in his ' Gen. Ame- rican Plants,' p. '217 (note), says that, whilst collecting- this plant in its native home, " I had occa- sion to observe that a detached leaf would make repeated efforts towards disclosing itself to the influence of the sun ; these at- tempts consisted in an undula- tory motion of the marginal cilias, accompanied by a partial open- ing and succeeding collapse of the lamina, which at length ter- minated in a complete expansion and in the destruction of sensi* bility." I am indebted to Prof. Oliver for this reference ; but I da riot understand what took

leaves thus treated re-expanded, — one to a partial ex- tent in 24 hrs., — a second to the same extent in 48 hrs., — and the third, which had been previously in- jured, 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 fila- ments, 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 Segin 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 80° to each other ; and on immersing it as before, the angle suddenly increased to 90°. A third leaf svas torpid from having recently re-expanded after having caught a fly, so that repeated touches of the filaments caused not the least movement ; never- theless, when similarly immersed, the lobes separated a little. As these leaves were inserted perpendicularly into the boiling water, both surfaces and the filaments

must have been equally affected ; and 1 can under- stand 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 back- wards ; 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 com- pared. Captures crustaceans — Structure of the leaves in comparison with those of Dionsea — Absorption by the glands, by the quaclrifid pro- cesses, 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 hrs., but only, as it appears, when inor- ganic 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 larvae.f Plants which had been kept in filtered water were placed by him in a vessel con-

* Since his original publication, cliioccioline are fresh-water mol- Stein has found out that the irri- luscs. It would be interesting to tability of the leaves was observed know whether their shells are at by De Sassus, as recorded in all corroded by the acid of the 1SGI. Uelpino states in a paper f I am greatly indebted to this published in 1871 (' Nuovo Ciior- distinguished naturalist for having nale Bot. Ital.' vol. iii. p. 171) sent me a copy of his memoir on

that " una quantita di chioccio- Aldrovanda, before its publica- line e di altri animalcoli acqua- tion in his ' Beitrage zur Biologie tici" are caught and suffocated der Pflanzen,' drittes Heft, 1875, 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 re- ceived 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 Dionrea.

Aldrovauda is destitute of roots and floats freely in the water. The leaves are arranged in whorls round the stern. Their broad petioles terminate in from four to six rigid projections,* each tipped with a stiff, short bristle. The bilobed leaf, with the midrib like- wise 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 Dionrca ; and this must make the capture of aquatic animals more easy. The outside of the leaves and the petioles are covered with minute twro-arnied papilla?, evidently answering to the eight-rayed papillas of Diona3a.

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 discus- 1861, p. 14G) believes that they sion by botanists on the homologi- correspond with the firnbriated col nature of these projections scale-like bodies found at the Dr. Kitschko (' Bot. Zeitung, buses of the petioles of Drosera. is slightly concave, and is formed, according to Colin, of three layers of cells. Its upper surface is studded with colourless glands like, but more simple than, those of Dionrca; they are supported on distinct footstalks, consisting of two rows of cells. The outer

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 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 re- semble 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 in-folded 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 Kubus. 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 com- posed of very delicate and highly flexible membrane, which can be easily bent or quite doubled back with- out 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 circum- ferential 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 Dionsea, as these latter are pro- longations of the blade, and not mere epidermic productions. They appear also to serve for a widely different purpose.

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 re- marks, 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 vas- cular tissue. They differ also from the six sensitive filaments of Dionrea in being colourless, and in having a medial as well as a basal articulation. No doubt it is owing to these two articulations that, notwithstand- ing 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 ex- amining 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 ru. 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 Dionsea. 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

already soluble animal matter. The included water would thus be pressed out, and the secretion conse- quently 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 proto- plasm was somewhat shrunk before they were im- mersed. 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 sub- stance 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 quad- rifids are situated, or within the closed concavity. In the latter case, water charged with excrementitioua 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 Diomea. Foul water would also be apt to ooze out at all times, especially when bubbles of air were generated within the concavity.

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 im- mersed 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, irre- gular, 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 con- tained 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 proto- plasm was a little shrunk and included yellowish specks ; and those which were before empty now con tained 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 con- tained 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

agrees with what I have observed under similar cir- stances 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 ex- amined 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 indistinguish- able from their delicacy and from having shrivelled ; for they were quite distinct on one leaf under circum- stances 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 chiti- QOUS integuments were as clean as if they had been 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 pro- cesses, from being partly filled with brown granular vmtter, 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 con- tained brownish granular matter. We thus gain additional evidence that the glands, the quadrifid pro- cesses, 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 unarti- culated 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 decaved. 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 Algse, still of a green- ish 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 Euro- pean ; namely in the projections at the upper end of the petiole being much attenuated and covered with 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 fore- going 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 Dionrea, 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 Dio- naea, — 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 con- dition 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 pro- cesses absorb excrementitious and decaying animal matter. It is a more curious fact that the points oa

the infolded margins apparently serve to absorb de- cayed animal matter in the same manner as the quad- rifids. 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 sur- faces must be liable to be irrigated by foul water flowing from the concavity of the leaf when it con- tains 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 under- stand 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 Utri- cularia, belonging to the same family, have been adapted for these two different functions.

Drosophyllum — Structure of leaves — Nature of the secretion — Man- ner of catching insects — Power of absorption — Digestion of animal substances — Summary on Drosophyllum — Roridula — Byblis — Glandular hairs of other plants, their power of absorption — Saxi- traga — Primula — Pelargonium — Erica — Mirabilis — Nicotianu — Summary on glandular hairs — Concluding remarks on the Dro- eeraceaa. 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 men- tioned members of the same family of the Droserace*. The leaves arise from an almost woody axis ; thev

are linear, much attenuated towards their tips, and several inches in length. The upper surface is con- cave, 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 resem- blance 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 sur- faces are convex, and the lower flat or even concave, so that they resemble miniature mushrooms in appear- ance. 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

vessels which run up the green multi- cellular pedicels. The glands secrete Part of leaf, enlarged seven times, show- ing lower surface. and indeed the two sets almost graduate into one another. But the sessile glands differ in one im- portant 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 Diona3a 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 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.