Insectivorous Plants

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 y^ 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 campho- rated 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 cam- phor 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 solu- tion, 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.

Length of Time between the Act of Brushing and the Inflection of the Tentacles. 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 move- ment 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 largo 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, BO was brushed, and in 4 m. was grandly inflected. A third leaf, after an immersion of 17 m., likewise showed no signs of in- flection ; 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 ten- tacles 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 vaponr of some bits of camphor (about as large as a filbert-nut), under a vessel holding ten fluid ounces. 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 wag wine inflection, which became moderately pronounced in two 01 three additional minutes. After 14 ra. al! five leaves were well, and some of them closely, inflected. After 6 hrs. the glands were white, and much mucus liad 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. Tnrjmitinp.— 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 ten- tacles 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 colour- less. Minute drops (about -^ 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 mix- ture 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 colour- less. 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 in- flection; 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 tin 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, espe- cially 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 pro- toplasm 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 sub- sequent action of the phosphate, or of splinters of glass placed on the glands ; but in two instances an immersion for 50 m. pre- vented 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 wator

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; ths 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 an- other when subsequently placed in the phosphate solution. I here give a table summing up the results.

In a large majority of these twenty cases, a varying degree of inflection was slowly caused by the phosphate. In four case8, 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 phos- phate 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 pro- duced, 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? Ox

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 -ian quickly pass into glands which, from having been immersed for 20 in. in a weak solution of sugar, either absorb the phos- phate 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 potas- sium 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 in- flected. 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 By allowing a precipitation of experiments on the production of sulphate of barium to take place artificial cells, and on their per- at the same time, the membrane meability to various salts, de- becomes "infiltrated" with this scribed in his papers : " Experi- salt ; and in consequence of the mente zur Theorie cler Zellenbil- intercalation of molecules of sul- dung und Kndosmose," Breslau, phate of barium among those of I860'; and " Experiment© zur the gelatine precipitate, the mole- physicalischen Erklarung cler Bil- cular interstices in the membrane dung der Zellhaut, ihres Wachs- are made smaller. In this altered thums durch Intussusception," condition, the membrane no longer Breslau, 1874. These researches allows the passage through it of perhaps explain my results. Dr. either sulphate of ammonia or Traube commonly employed as a nitrate of barium, though it re- membrane the precipitate formed tains its permeability for \vatei when tannic acid comes into con- and chloride of ammonia. tact with a solution of gelatine.

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 iu 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 anassthethic 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 diu-ing 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 ot 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 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 nil.), 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 perpen- dicularly 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

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 2m. 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 tirst 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, except- ing one which was ultimately a little inflected. The glands of the other tentacles continued to secrete, and appeared uninjured, out the whole plant after three days became very sickly.

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 5m. 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 lir. 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 ansesthetic 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 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 tho seven tentacles with meat were well inflected. From the slow- ness 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 ro.; 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 brs. 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.