Insectivorous Plants

by Charles Darwin

completely re-expanded, but the glands were much discoloured. Hence this salt is not poisonous in any high degree. The different action of the three foregoing salts of quinine is singular.

Digitaline.—Half-minims of a solution of one part to 437 of water were placed on the discs of five leaves. In 3 hrs. 45 m. Some of them had their tentacles, and one had its blade, moderately inflected. After 8 hrs. three of them were well inflected; the fourth had only a few tentacles inflected, and the fifth (an old leaf) was not at all affected. They remained in nearly the same state for two days, but the glands on their discs became pale. On the third day the leaves appeared much injured. Nevertheless, when bits of meat were placed on two of them, the outer tentacles became inflected. A minute drop (about 1/20 of a minim) of the solution was applied to three glands, and after 6 hrs. all three tentacles were inflected, but next day had nearly re-expanded; so that this very small dose of 1/28800 of a grain (.00225 mg.) acts on a tentacle, but is not poisonous. It appears from these several facts that digitaline causes inflection, and poisons the glands which absorb a moderately large amount.

Nicotine.—The secretion round several glands was touched with a minute drop of the pure fluid, and the glands were instantly blackened; the tentacles becoming inflected in a few minutes. Two leaves were immersed in a weak solution of two drops to 1 oz., or 437 grains, of water. When examined after 3 hrs. 20 m., only twenty-one tentacles on one leaf were closely inflected, and six on the other slightly so; but all the glands were blackened, or very dark-coloured, with the protoplasm in all the cells of all the tentacles much aggregated and dark-coloured. The leaves were not quite killed, for on being placed in a little solution of carbonate of ammonia (2 grs. to 1 oz.) a few more tentacles became inflected, the remainder not being acted on during the next 24 hrs.

Half-minims of a stronger solution (two drops to 1/2 oz. of water) were placed on the discs of six leaves, and in 30 m. all those tentacles became inflected; the glands of which had actually touched the solution, as shown by their blackness; but hardly any motor influence was transmitted to the outer tentacles. After 22 hrs. most of the glands on the discs appeared dead; but this could not have been the case, as when bits of meat were placed on three of them, some few of the outer tentacles were inflected in 24 hrs. Hence nicotine has a great tendency to blacken the glands and to induce aggregation [page 204] of the protoplasm, but, except when pure, has very moderate power of inducing inflection, and still less power of causing a motor influence to be transmitted from the discal glands to the outer tentacles. It is moderately poisonous.

Atropine.—A grain was added to 437 grains of water, but was not all dissolved; another grain was added to 437 grains of a mixture of one part of alcohol to seven parts of water; and a third solution was made by adding one part of valerianate of atropine to 437 of water. Half-minims of these three solutions were placed, in each case, on the discs of six leaves; but no effect whatever was produced, excepting that the glands on the discs to which the valerianate was given were slightly discoloured. The six leaves on which drops of the solution of atropine in diluted alcohol had been left for 21 hrs. were given bits of meat, and all became in 24 hrs. fairly well inflected; so that atropine does not excite movement, and is not poisonous. I also tried in the same manner the alkaloid sold as daturine, which is believed not to differ from atropine, and it produced no effect. Three of the leaves on which drops of this latter solution had been left for 24 hrs. were likewise given bits of meat, and they had in the course of 24 hrs. a good many of their submarginal tentacles inflected.

Veratrine, Colchicine, Theine.—Solutions were made of these three alkaloids by adding one part to 437 of water. Half-minims were placed, in each case; on the discs of at least six leaves, but no inflection was caused, except perhaps a very slight amount by the theine. Half-minims of a strong infusion of tea likewise produced, as formerly stated, no effect. I also tried similar drops of an infusion of one part of the extract of colchicum, sold by druggists, to 218 of water; and the leaves were observed for 48 hrs., without any effect being produced. The seven leaves on which drops of veratrine had been left for 26 hrs. were given bits of meat, and after 21 hrs. were well inflected. These three alkaloids are therefore quite innocuous.

Curare.—One part of this famous poison was added to 218 of water, and three leaves were immersed in ninety minims of the filtered solution. In 3 hrs. 30 m. some of the tentacles were a little inflected; as was the blade of one; after 4 hrs. After 7 hrs. the glands were wonderfully blackened, showing that matter of some kind had been absorbed. In 9 hrs. two of the leaves had most of their tentacles sub-inflected, but the inflection did not increase in the course of 24 hrs. One of these leaves, after being immersed for 9 hrs. in the solution, was placed in water, and by next morning had largely re-expanded; [page 205] the other two, after their immersion for 24 hrs., were likewise placed in water, and in 24 hrs. were considerably re-expanded, though their glands were as black as ever. Half-minims were placed on the discs of six leaves, and no inflection ensued; but after three days the glands on the discs appeared rather dry, yet to my surprise were not blackened. On another occasion drops were placed on the discs of six leaves, and a considerable amount of inflection was soon caused; but as I had not filtered the solution, floating particles may have acted on the glands. After 24 hrs. bits of meat were placed on the discs of three of these leaves, and next day they became strongly inflected. As I at first thought that the poison might not have been dissolved in pure water, one grain was added to 437 grains of a mixture of one part of alcohol to seven of water, and half-minims were placed on the discs of six leaves. These were not at all affected, and when after a day bits of meat were given them, they were slightly inflected in 5 hrs., and closely after 24 hrs. It follows from these several facts that a solution of curare induces a very moderate degree of inflection, and this may perhaps be due to the presence of a minute quantity of albumen. It certainly is not poisonous. The protoplasm in one of the leaves, which had been immersed for 24 hrs., and which had become slightly inflected, had undergone a very slight amount of aggregation—not more than often ensues from an immersion of this length of time in water.

Acetate of Morphia.—I tried a great number of experiments with this substance, but with no certain result. A considerable number of leaves were immersed from between 2 hrs. and 6 hrs. in a solution of one part to 218 of water, and did not become inflected. Nor were they poisoned; for when they were washed and placed in weak solutions of phosphate and carbonate of ammonia, they soon became strongly inflected, with the protoplasm in the cells well aggregated. If, however, whilst the leaves were immersed in the morphia, phosphate of ammonia was added, inflection did not rapidly ensue. Minute drops of the solution were applied in the usual manner to the secretion round between thirty and forty glands; and when, after an interval of 6 m:, bits of meat, a little saliva, or particles of glass, were placed on them, the movement of the tentacles was greatly retarded. But on other occasions no such retardation occurred. Drops of water similarly applied never have any retarding power. Minute drops of a solution of sugar of the same strength (one part to 218 of water) sometimes retarded the subsequent action of meat and of particles of glass, and [page 206] sometimes did not do so. At one time I felt convinced that morphia acted as a narcotic on Drosera, but after having found in what a singular manner immersion in certain non-poisonous salts and acids prevents the subsequent action of phosphate of ammonia, whereas other solutions have no such power, my first conviction seems very doubtful.

Extract of Hyoscyamus.—Several leaves were placed, each in thirty minims of an infusion of 3 grs. of the extract sold by druggists to 1 oz. of water. One of them, after being immersed for 5 hrs. 15 m., was not inflected, and was then put into a solution (1 gr. to 1 oz.) of carbonate of ammonia; after 2 hrs. 40 m. it was found considerably inflected, and the glands much blackened. Four of the leaves, after being immersed for 2 hrs. 14 m., were placed in 120 minims of a solution (1 gr. to 20 oz.) of phosphate of ammonia; they had already become slightly inflected from the hyoscyamus, probably owing to the presence of some albuminous matter, as formerly explained, but the inflection immediately increased, and after 1 hr. was strongly pronounced; so that hyoscyamus does not act as a narcotic or poison.

Poison from the Fang of a Living Adder.—Minute drops were placed on the glands of many tentacles; these were quickly inflected, just as if saliva had been given them, Next morning, after 17 hrs. 30 m., all were beginning to re-expand, and they appeared uninjured.