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Show 266 DROSERA ROTUNDIFOLIA. CHAP. XI. one part of the leaf to another 1nust be different fro1n that which actually induces aggregation. The process does not depend on the glands secreting more copiously than they did before ; and is independent of the inflection of the tentacles. It continues as long as the tentacles remain inflected, and as soon as these are fully re-expanded, the little 1nasses of protoplasm are all redissolved ; the cells becoming :filled with ho1nogeneous purple fluid, as they were before the leaf was excited. As the process of aggregation can be excited by a few touches, or by the pressure of insoluble particles, it is evidently independent of the absorption of any 1natter, and must be of a molecular nature. Even when caused by the absorption of the carbonate or other salt of ammonia, or an infusion of meat, the process seems to be of exactly the same nature. The protoplasmic fluid must, therefore, be in a singularly unstable condition, to be acted on by such slight and varied causes. Physiologists believe that when a nerve is touched, and it transmits an influence to other parts of the nervous system, a molecular change is induced in it, though ~ot visible to us. Therefore it is a very interesting spectacle to watch the effects on the cells of a gland, of the pressure of a bit of hair, weighing only 78 ~ 00 of a grain and largely supported by the dense secretion, for this excessively slight pressure s?on causes a visible change in the protoplasm, which change is transmitted down the whole length of the tentacle, giving it at last a mottled appearance, distinguishable even by the naked eye. In the fourth chapter it was shown that leaves placed for a short time in water at a temperature of llOo Fahr. ( 43°·3 Cent.) become somewhat inflected; they are thus also rendered more sensitive to the action CHAP. XI. GENERAL SUMMARY. 267 of meat than they wore before. If exposed to a teinperature of between 115° and 125° .C46o·1-51o·6 Cent.), they are quickly inflected, and theu proto~lasm undergoes aggregation; when afterwards placed In cold wat.er, they re-expand. Exposed to 130° (54°·4 Cent.), no Inflection immediately occurs, but the leaves are only temporarily paralysed, for on bein? left in cold water, they often become inflected and afterwards re-expand. In one leaf thus treated, I distinctly saw the protoplasm in movement. In other leaves, treated in the same manner, and then immersed in a solution of carbonate of amn1onia, strong aggregation ensued. L~aves placed in cold water, after an exposure to so high a temperature as 145° (62°·7 Cent.), sometiines become slightly, though slowly, inflected; and afterwards have the contents of their cells strongly aggregated by carbonate of ammonia. But the duration of the iinmersion is an important element, for if left in wate~ ~t 145° (62°·7 Cent.), or only at 140° (60° Cent.), until It becomes cool, they are killed, and the content.s of the glands are rendered white and opaq~e. This latter result seems to be due to the coagulation of the albumen, and was almost always caused by even a short exposure to 150° (65°·5 Cent.); but different le~ves, and even the separate cells in the same tentacle, d1ffer considerably in their power of resisting heat. Unless the heat has been sufficient to coagulate the albumen,. carbonate of ammonia subsequently induces aggregation. In the :fifth chapter, the results of placing ~rops. of various nitrogenous and non-nitrogenous ~rganic fluids on the discs of leaves were given, and It was shown that they detect with almost unerring certainty the presence of nitrogen. A decoction of green peas or of fresh cabbao-e-leaves acts almost as powerfully as an infusion of ra; meat; whereas an infusion of cabbage- , |