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Show 268 DROSERA ROTUNDIFOLIA. .OnA.P. XI. leaves made by keeping them for a long time in merely warm water is far less efficient. A decoction of grass-leaves is less powerful than one of green peas or cabbage-leaves. These results led me to inquire whether Drosera possessed the power of dissolving solid animal matter. The experiments proving that the leaves are capable of true digestion, and that the glands absorb the .digested matter, are given in detail in the sixth chapter. These are, perhaps, the most interesting of all my observations on Drosera, as no such power was before distinctly known to exist in the vegetable kingdom. It is likewise an interesting fact that the glands of tho disc, when irritated, should transinit some influence to the glands of the exterior tentacles, causing thmn io secrete more copiously and the secretion to become .acid, as if they had been directly excited by an obJect placed on thmn. The gastric juice of animals contains, as is well known, an acid and a ferment, both of which are indispensable for di()'ostion and so it is with the secretion of Drosera. When th~ stomach of an animal is mechanically irritatocl, it secretes an acid, and when particles of glass or other such objects were placed on the glands of Drosera, the secretion, and that of the surrounding and unto~ ched glands, was increased in quantity and became acid. But, according to Schiff, the stomach of an anir:nal doe.s . not secrete its proper ferment, pepsin, until certain substances, which he calls poptogonos, are absorbed; and it appears from Iny oxporin1ents that some Inatter must ~e absorbed by tho glands of Drosera befo~·e they secrete their proper ferment. That ~he secretion does contain a fern1ent which acts onlY In the presence of an acid on solid ani1nal matter, was clearly prov-ed by adding minute doses of CnAP. XI. GENERAL SUMMARY. 269 an alkali, which entirely arrested the process of digestion, this irnmediately recommencing as soon as the alkali was neutralised by a little weak hydrochloric acid. From trials made with a large number of substances, it was found that those which the secretion of Drosera dissolves completely, or partially, or not at all, are acted on in exactly the same manner by gastric juice. We may, therefore, conclude that the ferment of Drosera is closely analogous to, or identical ·with, the pepsin of animals. The substances which are digested by Drosera act on the leaves very differently. Some cause much tnore energetic and rapid inflection of the tentacles, and keep them inflected for a much longer time, than do others . . We are thus led to believe that the former are more nutritious than the latter, as is known to be the case with some of these same substances when given to animals; for instance, meat in comparison with gelatine. A.s cartilage is so tough a substance and is so little acted on by water, its prompt dissolution by the secretion of Drosera, and subsequent absorption, is, perhaps, one of the most striking cases. But it is not really more remarkable than the digestion of meat, which is dissolved by this secretion in the saine manner and by the saine stages as by gastric juice. The secretion dissolves bone, and even the enamel of teeth, but this is simply clue to the large quantity of acid secreted, owing, apparently, to the desire of the plant for phosphorus. In the case of bone, the ferment does not come into play until all the phosphate of lime has been decomposed and free acid is present, and then the fibrous basis is quickly dissolved. Lastly, the secretion attacks and dissolves matter out of living seeds, which it sometimes kills, or injures, as shown by the diseased state |