Chapter IX (2)

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]