Insectivorous Plants

Page 87

158 DROSERA ROTUNDIFOLIA. CHAP. VII. after the 8 hrs. it was impossible to comp~re the two lots, and doubt for an instant the power of the ~olutwn. . Two of the above leaves in the solutiOn had all their tentacles, except. three and four, inflect~d :Vithin an hour. I counted their glands and on the same pnnmple as before, each gland on one leaf cduld have absorbed only rr 6 l 8 00 , and on the other leaf Only of a grain of the phosphate. 1 4 72000' . 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 wer~ tried ~ecau~e I was then under the false impression that It was Incredible that any weaker solution could produce an effect. Each leaf received 80~ 0 of a grain, or ·00~1 mg. _The first eight. lea~es 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 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 r endered extremely sensitive. Special precautions were taken for this set of experi­tnents; 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 fi nest were immersed in water, and the next four finest in tho 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- . CHAP. VII. PHOSPHATE OF AMMONIA • 159 fleeted, 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. 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 tore-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. 1H m. about twenty-eight outer tentacles inflected; after 5 hrs. 20m. 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 38m. twenty-eight tentaclesl inflected; after 3 hrs. 45 m. thirty-three inflected, with most of the submarginal tentacles sub-inflected ; continued so for two days, and then partially re-expanded. (9) After 3H m. forty-two tentacles inflected; after 3 hrs. 12 m. sixty-six inflected or sub-inflected ; after 6 hrs. 40 m. all but twenty-four inflected or sub-inflected; after 9 hrs. 40 m. all but seventeen inflected; after 24 hrs. all but four inflected or sub-inflected, only a few being closely inflected; after 27 hrs. 40 m. the blade inflected. The leaf remained in this state for two days, and then began to re-expand. . (10) After 38 m. twenty-one tentacles inflected; after 3 hrs. 12m. forty-six tentacles inflected or sub-inflected; after 6 hrs. 40 m. all but seventeen inflected, though none closely; after 24 hrs. every tentacle slightly curved inwards ; after 27 hrs. 40 m. blade strongly inflected, and so continued for two days, and then the tentacle~ and blade very slowly re-expanded. (11) This fine dark l'ed and rather old leaf, though not ve1·y large, bore an extraordinary number of tentacles (viz. 252), and behaved in an anomalous manner. After 6 hrs. 40 m. only the short tentacles round the outer part of the disc were inflected, forming a ring, as so often occurs in from 8 to 24 hrs. with !eaves both in water and the weaker solutions. But after 9 hrs.