The plants were kept under the bell-glass for 24 hrs., but no further change ensued. One healthy leaf was hardly at all affected, though other leaves on the same plant were much affected. On some leaves all the tentacles on one side, but not those on the opposite side, were inflected. I doubt whether this extremely unequal action can be explained by supposing that the more active glands absorb all the vapour as quickly as it is generated, so that none is left for the others, for we shall meet with [page 143] analogous cases with air thoroughly permeated with the vapours of chloroform and ether.
Minute particles of the carbonate were added to the secretion surrounding several glands. These instantly became black and secreted copiously; but, except in two instances, when extremely minute particles were given, there was no inflection. This result is analogous to that which follows from the immersion of leaves in a strong solution of one part of the carbonate to 109, or 146, or even 218 of water, for the leaves are then paralysed and no inflection ensues, though the glands are blackened, and the protoplasm in the cells of the tentacles undergoes strong aggregation.
[We will now turn to the effects of solutions of the carbonate. Half-minims of a solution of one part to 437 of water were placed on the discs of twelve leaves; so that each received 1/960 of a grain or .0675 mg. Ten of these had their tentacles well inflected; the blades of some being also much curved inwards. In two cases several of the exterior tentacles were inflected in 35 m.; but the movement was generally slower. These ten leaves re-expanded in periods varying between 21 hrs. and 45 hrs., but in one case not until 67 hrs. had elapsed; so that they re-expanded much more quickly than leaves which have caught insects.
The same-sized drops of a solution of one part to 875 of water were placed on the discs of eleven leaves; six remained quite unaffected, whilst five had from three to six or eight of their exterior tentacles inflected; but this degree of movement can hardly be considered as trustworthy. Each of these leaves received 1/1920 of a grain (.0337 mg.), distributed between the glands of the disc, but this was too small an amount to produce any decided effect on the exterior tentacles, the glands of which had not themselves received any of the salt.
Minute drops on the head of a small pin, of a solution of one part of the carbonate to 218 of water, were next tried in the manner above described. A drop of this kind equals on an average 1/20 of a minim, and therefore contains 1/4800 of a grain (.0135 mg.) of the carbonate. I touched with it the viscid secretion round three glands, so that each gland received only [page 144] 1/14400 of a grain (.00445 mg.). Nevertheless, in two trials all the glands were plainly blackened; in one case all three tentacles were well inflected after an interval of 2 hrs. 40 m.; and in another case two of the three tentacles were inflected. I then tried drops of a weaker solution of one part to 292 of water on twenty-four glands, always touching the viscid secretion round three glands with the same little drop. Each gland thus received only the 1/19200 of a grain (.00337 mg.), yet some of them were a little darkened; but in no one instance were any of the tentacles inflected, though they were watched for 12 hrs. When a still weaker solution (viz. one part to 437 of water) was tried on six glands, no effect whatever was perceptible. We thus learn that the 1/14400 of a grain (.00445 mg.) of carbonate of ammonia, if absorbed by a gland, suffices to induce inflection in the basal part of the same tentacle; but as already stated, I was able to hold with a steady hand the minute drops in contact with the secretion only for a few seconds; and if more time had been allowed for diffusion and absorption, a much weaker solution would certainly have acted.
Some experiments were made by immersing cut-off leaves in solutions of different strengths. Thus four leaves were left for about 3 hrs.