Insectivorous Plants

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.45 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 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 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.46 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 considerable 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 shown47 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 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 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 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 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, 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.

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 may we not suppose48 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.