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Show 154 DROSERA ROTUNDIFOLIA. CHAP. VII. given, which are so ~urprisi~g that their credibility requires every ki.nd of support. I?-. 1872 I experimented on twelve Imm.ersed leaves? giving each only ten minims of a solut~on; but this was a bad method, for so small a quantity hardly covered them. None of these experiments will, therefore, be given, though they indicate that excessively minu~e doses are efficient. When I read over my notes, In 1873, I entirely disbelieved them, and determined to make another set of experiments with scrupulous care, on the same plan as those made with the nitrate; namely by placing leaves in watch-glas~es, and pou~·ing over each thirty minims of the solution under trial, treating at the same time and in the same manner other leaves with the distilled water used in making the solutions. During 1873, seventy-one leaves were thus tried in solutions of various strengths, and the same ntnnber in water. Notwithstanding the care taken and the number of the trials made, when in the following year I looked merely at the results, without reading over my observations, I again thought that there must have been some error, and thirty-five fresh trials were made with the weakest solution; but the results were as plainly marked as before. Altogether, 106 carefully selected leaves were tried, both in water and in solutions of the phosphate. Hence, after the most anxious consideration, I can entertain no doubt of the substantial accuracy of n1y results. Before giving my experiments, it may be well to premise that crystallised phosphate of ammonia, such as I used, contains 35·33 per cent. of water of crystallisation; so that in all the following trials the effieient elements formed only 64·67 per cent. of the salt used. Extremely minute particles of the dry phosphate were placed CHAP. VII. PHOSPHATE OF AMMONIA. 155 with the point of a needle on the secretion surrounding several glands. These poured forth much secretion, were blackened and ultimately died; but the tentacles moved only sEghtly: The dose, small as it was, evidently was too great, and the result was the . same as with particles of the carbonate of ammonia. Half-minims of a solution of one part to 437 of water were placed on the discs of three leaves and acted most energetically, causing the tentacles of one to be inflected ip 15 m., and the blades of all three to be much curved inwards in 2 hrs. 15m. Similar drops of a solution of one part to 1312 of water, (1 gr. to 3 oz.) were then placed on the discs of five leaves, so that each received the 2-i~;o of a grain ('0225 mg.). After 8 hrs. the tentacles of four of them were considerably inflected, and after 24 hrs. the blades of three. After 48 hrs. all five were almost fully re-expanded. I may mention with respect to one of these leaves, that a drop of water had beeu left during the previous 24 hrs. on its disc, but produced no effect; and that this was hardly dry when the solution was added. Similar drops of a solution of one part to 1750 of water (1 gr. to 4 oz.) were next placed on the discs of six leaves; so that each received 3 l 40 of a grain ('0169 mg.); after 8 hrs. three of them had many tentacles and their blades inflected; two others had only a few tentacles sljghtly inflected, and the sixth was not at all affected. After 24 h1·s. most of the leaves had a few more tentacles inflected, but one bad begun to re-expand. We thus see that with the more sensitive leaves the 3 -j40 of a grain, absor~ed by the central glands, is enough to make many of the exterior tentacles and the blades bend, whereas the 1 i 20 of a grain of the carbonate sjmilarly given produced no effect; and 2 lH 0 of a grain of the nitrate was only just sufficient to produce a well-marked effect. A minute drop, about equal to 21J of a minim, of a solution of one part of the phosphate to 875 of water, was applied to the secretion on three glands, each of which thus received only r; 7 ~ 00 of a grain ('00112 mg.), and all three tentacles became inflected. Similar drops of a solution of one part to 1312 of water (1 gr. to 3 oz.) were now tried on three leaves; a drop being applied to four glands on the same leaf. On the first leaf, three of the tentacles became slightly inflected in 6 m.-, and re-expanded after 8 brs. 45 m. On the second, two tentacles became sub-inflected in 12m. And on the third all four tentacles were decidedly inflected in 12 m.; they remained so for 8 hrs. 30m., but by the next morning were fully re-expanded. |