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Show 168 DROSERA ROTUNDIFOLIA. • CHAP, VII. salts of ammonia which were tried, all cause the inflection of the tentacles, and often of the blade of the leaf. As far as can be ascertained from the superficial trials with the last six salts, the citrate is the least powerful, and the phosphate certainly by far the most. The tartrate and chloride are remarkable from the short duration of their action. The relative efficiency of the carbonate, nitrate, and phosphate, is shown in the following table by the smallest a1nount which suffices to cause the inflection of the tentacles. Solutions, how applied. Carbonate of I Ammonia. Placed on the glands of/ D~u of a the disc, so as to act , gmin, or indirectly on the outerj . 067 5 mg. tentacles . . . . Applied f?~ a few se-J nb of a conds duectly to the grain or gland of an outer . 00445' mg. tentacle . • . . Nitrate of Ammonia. 2-loo of a grain, or ·027 mg. .ofa grain, or ·0025 mg. time allowed for each ~·:n, or ~~Tn~ 0~ Leaf immersed, with} 1 of a 1 f glan~ to absorb all · 00024 mg. · 0000937 mg. that It can . . . Amount absorbed by a\ gland which suffices 1 to cause the aggre- n:r\·~ of a gation of the proto- gram, or plasm in the adjoin- · 00048 mg. ing cells of the ten-tacles . . . . 1 Phosphate of Ammonia. "3"9\u of a grain, or ·0168 mg. T5'J~nu of a grain, or ·000423 mg. w1tkmm of a grain, or · 000003~8 mg. From the experiments tried in these throe different ways, we see that the carbonate, which contains 23·7 ·per cent. of nitrogen, is less efficient than the nitrate, which contains 35 per cent. The phosphate contains less nitrogen than either of these salts, namely, only 21·2 per cent., and yet is far more CHAP. VII. SUMMARY, SALTS OF AMMONIA • 169 efficient ; its power no doubt depending quite as much on the phosphorus as on the nitrogen which it contains. We may infer that this is the case, from . the energetic .manner in which bits of bone and phosphate of lime affect the leaves. The inflection excited by the other salts of ammonia is probably due solely to their nitrogen,- on the same principle that nitrogenous organic fluids act powerfully, whilst non-nitrogenous organic fluids are powerless. As such minute closes of the salts of ammonia affect the leaves, we may feel almost sure that Drosera absorbs and profits by the amount, though small, which is present in rain-water, in the same manner as other plants absorb these same salts by their roots. The smallness of the doses of the nitrate, and more especially of the phosphate of ammonia, which cause the tentacles of immersed leaves to be inflected is perhaps the most re1narkable fact recorded in this' volume. When we see that much less than the millionth* of a grain of the phosphate, absorbed by a gland of one of the exterior tentacles, causes it to bend, it may be thought that the effects of the solution on the glands of the disc have been over looked ; namely, the transmission of a motor impulse fron1 them to the exterior tentacles. No doubt the movements of the latter are thus aided ; but the aid thus rendered must be insignificant; for we know that a drop containing as much as the - 1- of a grain placed 3 tl 4 0 on the disc is only just able to cause the outer ten-tacles of a highly sensitive leaf to bend. It is cer- . * It is scarcely possible to realIse what a million means. The best illustration which I have met with is that given by Mr. Croll, who says,-'J;ake a narrow strip of paper ~3 ft. 4 in. in length, and stretch it along the wall of a large ·hall ; then mark off at one end the tenth of an inch. 'fhis tenth will represent a hundred, and the entire strip a million. |
