Chap. VII.] PHOSPHATE OP AMMONIA. 129 



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 solu- 

 tion could produce an effect. Each leaf received -gT^gjf of a grain, 

 or .0081 mg. The first eight leaves which I tried both in the solu- 

 tion and water were either young and pale or too old; and the 

 weather was not hot. They were hardly at all affected; never- 

 theless, it would be unfair to exclude them. I then waited until I 

 had got eight pairs of fine leaves, and the weather was favourable, 

 the temperature of the room where the leaves were immersed vary- 

 ing from 75 to 81 (23.8 to 27.2 Cent.). In another trial with 

 four pairs (included in the above twenty pairs), the temperature in 

 my room was rather low, about 60 (15.5 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 Professor 

 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 wjater speci- 

 mens 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 con- 

 dition 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 inflec'ted, or 

 plainly sub-inflected. After 4 hrs. the tentacles began to re-ex- 

 pand, 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. 17m. 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 inflet-ted. 



(6) After 40 m. some inflection; after 2 hrs. 18 m. about 



