Some solutions, for instance that of carbonate of ammonia, quickly discolour the glands; and as all on the same leaf were discoloured simultaneously, they must all have absorbed some of the salt within the same short period of time. This was likewise shown by the simultaneous inflection of the several exterior rows of tentacles. If we had no such evidence as this, it might have been supposed that only the glands of the exterior and inflected tentacles had absorbed the salt; or that only those on the disc had absorbed it, and had then transmitted a motor impulse to the exterior tentacles; but in this latter case the exterior tentacles would not have become inflected until some time had elapsed, instead of within half an hour, or even within a few minutes, as usually occurred. All the glands on the same leaf are of nearly the same size, as may best be seen by cutting off a narrow transverse strip, and laying it on its side; hence their absorbing surfaces are nearly equal. The long-headed glands on the extreme margin must be excepted, as they are much longer than the others; but only the upper surface is capable of absorption. Besides the glands, both surfaces of the leaves and the pedicels of the tentacles bear numerous minute papillae, which absorb carbonate of ammonia, an infusion of raw meat, metallic salts, and probably many other substances, but the absorption of matter by these papillae never induces inflection. We must remember that the movement of each separate tentacle depends on its gland being excited, except when a motor impulse is transmitted from the glands of the disc, and then the movement, as just stated, does not take place until some little time has elapsed. I have made these remarks because they show us that when a leaf is immersed in a solution, and the tentacles are inflected, we can judge with some accuracy how much of the salt each gland has absorbed. For instance, if a leaf bearing 212 glands be immersed in a measured quantity of a solution, containing 1/10 of a grain of a salt, and all the exterior tentacles, except twelve, are inflected, we may feel sure that each of the 200 glands can on an average have absorbed at most 1/2000 of a grain of the salt. I say at [page 139] most, for the papillae will have absorbed some small amount, and so will perhaps the glands of the twelve excluded tentacles which did not become inflected. The application of this principle leads to remarkable conclusions with respect to the minuteness of the doses causing inflection. _On the Action of Distilled Water in Causing Inflection._