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Show 136 DROSERA ROTUNDIFOLIA. CHAP. VII. CH.APTER VII. 'fHE EFFECTS OF SALTS OF AMMONIA. 1\fa.nner of performing the experiments- Action of cli::;tillecl water in comparison with the solutions- Carbonate of ammonia, absorbed by the roots- The vapour absorbed by the gland -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, analocrous experiments with- Other salts of ammonia- Summary and concluding remarks on the action of the salts of ammonia. rrHE chief object in this chapter is to show how powerfully the salts of a1nmonia act on the leav s of Drosera, and more especially to show what an extraordinarily s1nall quantity suffices to excite inflection. I shall, therefore, be compelled to enter into full details. Doubly distilled water was always used; and for the n1ore delicate experiments, water which had been prepared with the utmost possible care was given n1e 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 9 ~ 0 of a fluid ounce ('0286 mi.), were placed by the same pointed instrument on the CHAP. VII. SALTS OF AMMONIA. 137 discs of the leaves, and the inflection of the exterior rows of tentacles observed at successive intervals of time. It was first ascertained, from between thirty and forty trials, that distilled water dropped in this manner produces no effect, except that sometimes, though rarely, two or three tentacles become inflected. In fact all the many trials with solutions which were so weak as to produce no effect lead to the same result that water is inefficient. Secondly.-The head of a small pin, fixed into a handle, was dipped into the solution under trial. The small drop which adhered to it, and which was much too small to fall off, was cautiously placed, by the aid of a lens, in contact with the secretion surrounding the glands of one, two, three, or four of the exterior tentacles of the same leaf. Great care was taken that the glands themselves should not be touched. I had supposed that the drops were of nearly the same size; but on trial this proved a great mistake. I first measured some water, and removed 300 drops, touching the pin's head each time on blottingpaper; and on again measuring the water, a drop was found to equal on an average about the io of a minim. Some water in a small vessel was weighed (and this is a more accurate method), . and 300 drops removed as before ; and on again weighing the water, a drop was found to equal on an average only the -bi of a minim. I repeated the operation, but endeavoured this time, by taking the pin's head out of the water obliquely and rather quickly, to remove as lar~e drops as possible ; and the result showed that I had succeeded, for each drop on an average equalled 19 1 .4 of a minim. I repeated the operation in exactly the same manner, and now the drops averaged 2~·5 of a minim. Bearing in mind that on these two latter occasions special pains were taken to remove as large drops as possible, we may safely conclude that the drops used in my experiments were at least equal to the -;0 of a minim, or ·0029 ml. One of these drops could be applied to three or even four glands, and if the tentacles became inflected, some of the solution must have been absorbed by all; for drops of pure wa.ter, applied in the same manner, never produced any effect. I was able to hold the drop in steady contact with the secretion only for ten to fifteen seconds; and this was not time enough for the diffusion of all the salt in solution, as was evident, from three or four tentacles treated successively with the same drop, often becoming inflected. All the matter in solution was even then probably not exhausted. Thirdly.-Leaves were cut off and immersed in a measured |
