one had thirteen of its outer tentacles inflected; a second six, and four others either one or two inflected. After 8 hrs. the outer tentacles did not become more inflected; whereas this occurred with the leaves in the solution. I record in my notes that [page 158] after the 8 hrs. it was impossible to compare the two lots, and doubt for an instant the power of the solution.
Two of the above leaves in the solution had all their tentacles, except three and four, inflected within an hour. I counted their glands, and, on the same principle as before, each gland on one leaf could have absorbed only 1/1164800, and on the other leaf only 1/1472000, of a grain of the phosphate.
Twenty leaves were immersed in the usual manner, each in thirty minims of a solution of one part to 218,750 of water (1 gr. to 500 oz.). So many leaves were tried because I was then under the false impression that it was incredible that any weaker solution could produce an effect. Each leaf received 1/8000 of a grain, or .0081 mg. The first eight leaves which I tried both in the solution and in water were either young and pale or too old; and the weather was not hot. They were hardly at all affected; nevertheless, it would be unfair to exclude them. I then waited until I got eight pairs of fine leaves, and the weather was favourable; the temperature of the room where the leaves were immersed varying from 75o to 81o (23o.8 to 27o.2 Cent.) In another trial with four pairs (included in the above twenty pairs), the temperature in my room was rather low, about 60o (15o.5 Cent.); but the plants had been kept for several days in a very warm greenhouse and thus rendered extremely sensitive. Special precautions were taken for this set of experiments; a chemist weighed for me a grain in an excellent balance; and fresh water, given me by Prof. Frankland, was carefully measured. The leaves were selected from a large number of plants in the following manner: the four finest were immersed in water, and the next four finest in the solution, and so on till the twenty pairs were complete. The water specimens were thus a little favoured, but they did not undergo more inflection than in the previous cases, comparatively with those in the solution.
Of the twenty leaves in the solution, eleven became inflected within 40 m.; eight of them plainly and three rather doubtfully; but the latter had at least twenty of their outer tentacles inflected. Owing to the weakness of the solution, inflection occurred, except in No. 1, much more slowly than in the previous trials. The condition of the eleven leaves which were considerably inflected will now be given at stated intervals, always reckoning from the time of immersion:--
(1) After only 8 m. a large number of tentacles inflected, and after 17 m. all but fifteen; after 2 hrs. all but eight in- [page 159] flected, or plainly sub-inflected. After 4 hrs. the tentacles began to re-expand, and such prompt re-expansion is unusual; after 7 hrs. 30 m. they were almost fully re-expanded.
(2) After 39 m. a large number of tentacles inflected; after 2 hrs. 18 m. all but twenty-five inflected; after 4 hrs. 17 m. all but sixteen inflected. The leaf remained in this state for many hours.
(3) After 12 m. a considerable amount of inflection; after 4 hrs. all the tentacles inflected except those of the two outer rows, and the leaf remained in this state for some time; after 23 hrs. began to re-expand.
(4) After 40 m. much inflection; after 4 hrs. 13 m. fully half the tentacles inflected; after 23 hrs. still slightly inflected.
(5) After 40 m. much inflection; after 4 hrs. 22 m. fully half the tentacles inflected; after 23 hrs. still slightly inflected.
(6) After 40 m. some inflection; after 2 hrs. 18 m. about twenty-eight outer tentacles inflected; after 5 hrs. 20 m. about a third of the tentacles inflected; after 8 hrs. much re-expanded.
(7) After 20 m. some inflection; after 2 hrs. a considerable number of tentacles inflected; after 7 hrs. 45 m. began to re-expand.
(8) After 38 m.