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.]

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.

Citrate of Ammonia.—­Half-minims of a solution of one part to 437 of water were placed on the discs of six leaves.  In 1 hr. the short outer tentacles round the discs were a little inflected, with the glands on the discs blackened.  After 3 hrs. 25 m. one leaf had its blade inflected, but none of the exterior tentacles.  All six leaves remained in nearly the same state during the day, the submarginal tentacles, however, [page 167] becoming more inflected.  After 23 hrs. three of the leaves had their blades somewhat inflected; and the submarginal tentacles of all considerably inflected, but in none were the two, three, or four outer rows affected.  I have rarely seen cases like this, except from the action of a decoction of