When the two lots of eight leaves in the solution and in the water were compared after the lapse of 24 hrs., they undoubtedly differed much in appearance. The few tentacles on the leaves in water which were inflected had after this interval re-expanded, with the exception of one leaf; and this presented the very unusual case of the blade being somewhat inflected, though in a degree hardly approaching that of the two leaves in the solution. Of these latter leaves, No. 1 had almost all its tentacles, together with its blade, inflected after an immersion of 2 hrs. 30 m. Leaves No. 2 and 3 were affected at a much slower rate; but after from 24 hrs. to 48 hrs. almost all their tentacles were closely inflected, and the blade of one quite doubled up. We must therefore admit, incredible as the fact may at first appear, that this extremely weak solution acted on the more sensitive leaves; each of which received only the 1/80000 of a grain (.00081 mg.) of the phosphate. Now, leaf No. 3 bore 178 tentacles, and subtracting the three which were not inflected, each gland could have absorbed only the 1/14000000 of a grain, or .00000463 mg. Leaf No. 1, which was strongly acted on within 2 hrs. 30 m., and had all its outer tentacles, except thirteen, inflected within 6 hrs. 30 m., bore 260 tentacles; and on the same principle as before, each gland could have [page 166] absorbed only 1/19760000 of a grain, or .00000328 mg.; and this excessively minute amount sufficed to cause all the tentacles bearing these glands to be greatly inflected. The blade was also inflected.] A Summary of the Results with Phosphate of Ammonia.—The glands of the disc, when excited by a half-minim drop (.0296 ml.), containing 1/3840 of a grain (.0169 mg.) of this salt, transmit a motor impulse to the exterior tentacles, causing them to bend inwards. A minute drop, containing 1/153600 of a grain (.000423 mg.), if held for a few seconds in contact with a gland, causes the tentacle bearing this gland to be inflected. If a leaf is left immersed for a few hours, and sometimes for a shorter time, in a solution so weak that each gland can absorb only the 1/9760000 of a grain (.00000328 mg.), this is enough to excite the tentacle into movement, so that it becomes closely inflected, as does sometimes the blade. In the general summary to this chapter a few remarks will be added, showing that the efficiency of such extremely minute doses is not so incredible as it must at first appear. [Sulphate of Ammonia.—The few trials made with this and the following five salts of ammonia were undertaken merely to ascertain whether they induced inflection. Half-minims of a solution of one part of the sulphate of ammonia to 437 of water were placed on the discs of seven leaves, so that each received 1/960 of a grain, or .0675 mg. After 1 hr. the tentacles of five of them, as well as the blade of one, were strongly inflected. The leaves were not afterwards observed.