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Show G2 DROSERA RO'fUNDIFOLIA. CHAP. III. the glands,--by the glands ~bsorb_ing various flui<ls or 111atter dissol ve<l out of certain bo(hes,-by exosnlose,and by a certain degree of heat. On the other han<l, a temperature of about 150° ] ahr. (G5o·5 C nt.) <l.oes not excite aggregation ; nor does the. sudden cruslnng of a gland. If a cell is rupturo<l, :1e1th~r ~he exuded. 111atter nor that which still remains within tho cell undergoes ao·oTegation when carbonate of amrnonia is added. A v~~y strong solution of this salt and rather large bits of raw meat prevent the a?gregate<l 1nassos beino· well developed. From th se facts we may conclud~ that the protoplasmic fluid within a cell does not become aggregated unless it be in a. l~ving state, and only imperfect! y if the cell has been In J urod. We have also seen that the fluid must be in an oxygenated state, in order that the process of aggregation should travel from cell to cell at the proper rate. Various nitrogenous organic fluids an<l salts of ammonia induce aggregation, but in different degrees and at very different rates. Carbonate of ammonia is the most powerful of all known substances ; the a1- sorption of Ts&oo of a grain (·000482 mg.) by a gland suffices to cause all the cells of the same t entacle to become aggregated. The first effect of tho carbonate and of certain other salts of ammonia, as well as of some other fluids, is the darkening or blackening of the glands. This follows even from long immersion in cold distilled water. It apparently depends ju chief part on the strong aggr gation of their eollcontents, which thus become opaque, an<l do not reflect light. Some other fluids render tho glan<ls of a brighter red; whilst certain acids, though much diluted, the poison of the cobra-snake, &c., make the glands perfectly white and opaque; and this sooms to depend on the coagulation of their contents without CHAP. III. 'rHE PROCESS OF AGGREGATION. 63 any1 aggregation. Nevertheless, before being thus affected, they are able, at least in some cases, to excite aggregation in their own tentacles. That the central glands, if irritated, send centrifugally some influence to the exterior glands, causing them to send back a centripetal influence inducing aggregation, is perhaps the most interesting fact given in this chapter. But the whole process of aggregation is in itself a striking phenomenon. Whenever the peripheral extremity of a nerve is touched or pressed, and a sensation is felt, it is believed that an invisible molecular change is sent from one end of the nerve to the other; but when a gland of Drosera is repeatedly touched or gently pressed, we can actually see a molecular change proceeding from the gland down the tentacle ; though this change is probably of a very different nature from that in a nerve. Finally, as so many and such widely different causes excite aggregation, it would appear that the living matter within the gland-cells is in so unstable a condition that almost any disturbance suffices to change its molecular nature, as in the case of certain chemical compounds. And this change in the glands, whether excited directly, or indirectly by a stimulus received from other glands, is transmitted from cell to cell, causing granules of protoplasm either to be actually genera ted in the previous! y limpid fl uicl or to coalesce and thus to become visible. Supplernentary Observations on the Process of Aggregation in the Roots of Plants. It will hercnJter be seen that a weak solution of the carbonate of ammonia induces aggregation in the cells of the roots of Drosera; and this led me to make a few trials on the roots of other plants. I dug up jn the latter part of October the first weed which I met with, viz. Euphorbia pepl'Us, being care- |
