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rates and in very different degrees; and the tentacles remain inflected for very different periods of time. Quick inflection depends partly on the quantity of the substance given, so that many glands are simultaneously affected, partly on the facility with which it is penetrated and liquefied by the secretion, partly on its nature, but chiefly on the presence of exciting matter already in solution. Thus saliva, or a weak solution of raw meat, acts much more quickly than even a strong solution of gelatine. So again leaves which have re-expanded, after absorbing drops of a solution of pure gelatine or isinglass (the latter being the more powerful of the two), if given bits of meat, are inflected much more energetically and quickly than they were before, notwithstanding that some rest is generally requisite between two acts of inflection. We probably see the influence of texture in gelatine and globulin when softened by having been soaked in water acting more quickly than when merely wetted. It may be partly due to changed texture, and partly to changed chemical nature, that albumen, which has been kept for some time, and gluten which has been subjected to weak hydrochloric acid, act more quickly than these substances in their fresh state.

The length of time during which the tentacles remain inflected largely depends on the quantity of the substance given, partly on the facility with which it is penetrated or acted on by the secretion, and partly on its essential nature. The tentacles always remain inflected much longer over large bits or large drops than over small bits or drops. Texture probably plays a part in determining the extraordinary length of time during which the tentacles remain inflected

over the hard grains of chemically prepared casein. But the tentacles remain inflected for an equally long time over finely powdered, precipitated phosphate of lime; phosphorus in this latter case evidently being the attraction, and animal matter in the case of casein. The leaves remain long inflected over insects, but it is doubtful how far this is due to the protection afforded by their chitinous integuments; for animal matter is soon extracted from insects (probably by exosmose from their bodies into the dense surrounding secretion), as shown by the prompt inflection of the leaves. We see the influence of the nature of different substances in bits of meat, albumen, and fresh gluten acting very differently from equal-sized bits of gelatine, areolar tissue, and the fibrous basis of bone. The former cause not only far more prompt and energetic, but more prolonged, inflection than do the latter. Hence we are, I think, justified in believing that gelatine, areolar tissue, and the fibrous basis of bone, would be far less nutritious to Drosera than such substances as insects, meat, albumen, &c. This is an interesting conclusion, as it is known that gelatine affords but little nutriment to animals; and so, probably, would areolar tissue and the fibrous basis of bone. The chondrin which I used acted more powerfully than gelatine, but then I do not know that it was pure. It is a more remarkable fact that fibrin, which belongs to the great class of Proteids, including albumen in one of its sub-groups, does not excite the tentacles in a greater degree, or keep them inflected for a longer time, than does gelatine, or

*

* See the classification adopted by Dr. Michael Foster in Watts' Dict. of Chemistry,' Supplement 1872, p. 969.

areolar tissue, or the fibrous basis of bone. It is not known how long an animal would survive if fed on fibrin alone, but Dr. Sanderson has no doubt longer than on gelatine, and it would be hardly rash to predict, judging from the effects on Drosera, that albumen would be found more nutritious than fibrin. Globulin likewise belongs to the Proteids, forming another sub-group, and this substance, though containing some matter which excited Drosera rather strongly, was hardly attacked by the secretion, and was very little or very slowly attacked by gastric juice. How far globulin would be nutritious to animals is not known. We thus see how differently the above specified several digestible substances act on Drosera; and we may infer, as highly probable, that they would in like manner be nutritious in very different degrees both to Drosera and to animals.

The glands of Drosera absorb matter from living seeds, which are injured or killed by the secretion. They likewise absorb matter from pollen, and from fresh leaves; and this is notoriously the case with the stomachs of vegetable-feeding animals. Drosera is properly an insectivorous plant; but as pollen cannot fail to be often blown on to the glands, as will occasionally the seeds and leaves of surrounding plants, Drosera is, to a certain extent, a vegetablefeeder.

Finally, the experiments recorded in this chapter show us that there is a remarkable accordance in the power of digestion between the gastric juice of animals with its pepsin and hydrochloric acid and the secretion of Drosera with its ferment and acid belonging to the acetic series. We can, therefore, hardly doubt that the ferment in both cases is closely similar,

if not identically the same. That a plant and an animal should pour forth the same, or nearly the same, complex secretion, adapted for the same purpose of digestion, is a new and wonderful fact in physiology. But I shall have to recur to this subject in the fifteenth chapter, in my concluding remarks on the Droseraceæ.

7

CHAPTER VII.

THE EFFECTS OF SALTS OF AMMONIA.

Manner of performing the experiments - Action of distilled water in comparison with the solutions-Carbonate of ammonia, absorbed by the roots - The vapour absorbed by the glands - Drops on the disc-Minute drops applied to separate glands - Leaves immersed in weak solutions - Minuteness of the doses which induce aggregation of the protoplasm-Nitrate of ammonia, analogous experiments with — Phosphate of ammonia, analogous experiments with Other salts of ammonia Summary and concluding re

marks on the action of the salts of ammonia.

THE chief object in this chapter is to show how powerfully the salts of ammonia act on the leaves of Drosera, and more especially to show what an extraordinarily small quantity suffices to excite inflection. I shall, therefore, be compelled to enter into full details. Doubly distilled water was always used; and for the more delicate experiments, water which had been prepared with the utmost possible care was given me by Professor Frankland. The graduated measures were tested, and found as accurate as such measures can be. The salts were carefully weighed, and in all the more delicate experiments, by Borda's double method. But extreme accuracy would have been superfluous, as the leaves differ greatly in irritability, according to age, condition, and constitution. Even the tentacles on the same leaf differ in irritability to a marked degree. My experiments were tried in the following several ways.

Firstly.-Drops which were ascertained by repeated trials to be on an average about half a minim, or the of a fluid ounce (0296 ml.), were placed by the same pointed instrument on the

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