Two other experiments are worth giving.  A leaf was immersed for 4 hrs. 15 m. in distilled water, and there was no aggregation; it was then placed for 1 hr. 15 m. in a little solution of one part to 5250 of water; and this excited well-marked aggregation and inflection.  Another leaf, after having been immersed for 21 hrs. 15 m. in distilled water, had its glands blackened, but there was no aggregation in the cells beneath them; it was then left in six minims of the same solution, and in 1 hr. there was much aggregation in many of the tentacles; in 2 hrs. all the tentacles (146 in number) were affected—­the aggregation extending down for a length equal to half or the whole of the glands.  It is extremely improbable that these two leaves would have undergone aggregation if they had been left for a little longer in the water, namely for 1 hr. and 1 hr. 15 m., during which time they were immersed in the solution; for the process of aggregation seems invariably to supervene slowly and very gradually in water.]

Summary of the Results with Carbonate of Ammonia.—­The roots absorb the solution, as shown by their changed colour, and by the aggregation of the contents of their cells.  The vapour is absorbed by the glands; these are blackened, and the tentacles are inflected.  The glands of the disc, when excited by a half-minim drop (.0296 ml.), containing 1/960 of a grain (.0675 mg.), transmit a motor impulse to the exterior tentacles, causing them to bend inwards.  A minute drop, containing 1/14400 of a grain (.00445 mg.), if held for a few seconds in contact with a gland, soon causes the tentacle bearing it to be inflected.  If a leaf is left [page 148] immersed for a few hours in a solution, and a gland absorbs the 1/134400 of a grain (.0048 mg.), its colour becomes darker, though not actually black; and the contents of the cells beneath the gland are plainly aggregated.  Lastly, under the same circumstances, the absorption by a gland of the 1/268800 of a grain (.00024 mg.) suffices to excite the tentacle bearing this gland into movement.

[Nitrate of ammonia.

With the salt I attended only to the inflection of the leaves, for it is far less efficient than the carbonate in causing aggregation, although considerably more potent in causing inflection.  I experimented with half-minims (.0296 ml.) on the discs of fifty-two leaves, but will give only a few cases.  A solution of one part to 109 of water was too strong, causing little inflection, and after 24 hrs. killing, or nearly killing, four out of six leaves which were thus tried; each of which received the 1/240 of a grain (or .27 mg.).  A solution of one part to 218 of water acted most energetically, causing not only the tentacles of all the leaves, but the blades of some, to be strongly inflected.  Fourteen leaves were tried with drops of a solution of one part to 875 of water, so that the disc of each received the 1/1920 of a grain (.0337 mg.).  Of these leaves, seven were very strongly