of these glands could have received very little more than 1/153600 of a grain (or .000423); but this small quantity sufficed to cause inflection.  We must bear in mind that these drops were applied to the viscid secretion for only from 10 to 15 seconds, and we have good reason to believe that all the phosphate in the solution would not be diffused and absorbed in this time.  We have seen under the same circumstances that the absorption by a gland of 1/19200 of a grain of the carbonate, and of 1/57600 of a grain of the nitrate, did not cause the tentacle bearing the gland in question to be inflected; so that here again the phosphate is much more powerful than the other two salts.

We will now turn to the 106 experiments with immersed leaves.  Having ascertained by repeated trials that moderately strong solutions were highly efficient, I commenced with sixteen leaves, each placed in thirty minims of a solution of one part to 43,750 of water (1 gr. to 100 oz.); so that each received 1/1600 of a grain, or .04058 mg.  Of these leaves, eleven had nearly all or a great number of their tentacles inflected in 1 hr., and the twelfth leaf in 3 hrs.  One of the eleven had every single tentacle closely inflected in 50 m.  Two leaves out of the sixteen were only moderately affected, yet more so than any of those simultaneously immersed in water; and the remaining two, which were pale leaves, were hardly at all affected.  Of the sixteen corresponding leaves in water, one had nine tentacles, another six, and two others two tentacles inflected, in the course of 5 hrs.  So that the contrast in appearance between the two lots was extremely great.

Eighteen leaves were immersed, each in thirty minims of a solution of one part to 87,500 of water (1 gr. to 200 oz.), so that each received 1/3200 of a grain (.0202 mg.).  Fourteen of these were strongly inflected within 2 hrs., and some of them within 15 m.; three out of the eighteen were only slightly affected, having twenty-one, nineteen, and twelve tentacles in- [page 157] flected; and one was not at all acted on.  By an accident only fifteen, instead of eighteen, leaves were immersed at the same time in water; these were observed for 24 hrs.; one had six, another four, and a third two, of their outer tentacles inflected; the remainder being quite unaffected.

The next experiment was tried under very favourable circumstances, for the day (July 8) was very warm, and I happened to have unusually fine leaves.  Five were immersed as before in a solution of one part to 131,250 of water (1 gr. to 300 oz.), so that each received 1/4800 of a grain, or .0135 mg.  After an immersion of 25 m. all five leaves were much inflected.  After 1 hr. 25 m. one leaf had all but eight tentacles inflected; the second, all but three; the third, all but five; the fourth; all but twenty-three; the fifth, on the other hand, never had more than twenty-four inflected.  Of the corresponding five leaves in water, one had seven, a second two, a third ten, a