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Show 128 DROSERA RO'rUNDIFOLIA. CHAI. VI. much inflection; on the contrary, this served to a certain extent as a protection to the seeds. Two of the six .seeds germinated whilst still lying on the leaves, but the seedlings, when transferred to damp sand, soon died; of the other four seeds, only one germinated. Two seeds of mustard (Sin arJis nigrct), two of celery (Api-um ,qraveolens)-both of the previous year, two sec.ds well so~ked of caraway (Carum carui ), and two of wheat, d1d not exmte the leaves more than inorganic objects often do. Five seeds, hardly ripe, of a buttercup (RanunculnR), and two fresh seeds of Anemone nemorosrr., induced only a little more effect. On the other hand, four seeds, perhaps not quite ripe, of Oarf'x sylvat ica caused the leaves on which they were placed to be very strongly inflected; ani these only began to re~expand on the third day, one remaining inflected for seven days. It follows from these few facts that different kinds of seeds excite the leaves in very different degrees; whether this is solely due to the nature of their coats is not clear. In the case of tbe cress seeds, the partial removal of the layer of mucus hastened the inflection of the tentacles. Whenever the leaves remain inflected during several clays over seeds, it is clear that they absorb some matter from them. That the secretion penetrates their coats is also evident from the large proportion of cabbage, racldish, and cress seeds which were killed, and from several of the seedlings being greatly injured. This injury to the seeds and seedlings may, however, be dne solely to the acid of the secretion, and not to any process of digestion; for Mr. Tra herne Moggridge has shown that very weak acids of the acetic series are highly injurious to seeds. It never occurred to me to observe whether seeds are often blown on to the viscid leaves of plants growing in a state of nature; but this can hardly fail sometimes to occur, as we shall hereafter see in the case of Pinguicula. If so, Drosera will profit to a slight degree by absorbing matter from such seeds. Summary and Concluding Remarks on the Digestive Power of Drosera. When the glands on the disc are excited either by the absorption of nitrogenous matter or by mechanical irritation, their secretion increases in quantity and becomes acid. Th~y likewise transmit , CHAP. VI. DIGESTION. 129 some influence to the glands of the exterior tentac~ es, causi~g th.em ~o secrete more copiously; and their secretion hkewise becomes acid. With animals, according to Schiff,* mechanical irritation excites the glands of the stomach to secrete an acid but not pepsin. Now, I have every reason to be~ lieve (though the fact is not fully established), that ~ltho~g~ the ?lands of Drosera are continually secret~ Ing VISCid fluid to replace that lost by evaporation, yet .they do not secrete the ferment proper for eligestio~ when ~1echanically irritated, but only after absorbing certain matter, probably of a nitrogenous nature. I infer that this is the case, as the secretion from a large number of leaves which had been irritated by particles of glass placed on their discs did not digest album en ; and more especially from the analogy of Dionrea and Nepenthes. In like manner, the glands of the stomach of animals secrete pepsin, as Schiff asserts, only after they have absorbed certain soluble substances, which he designates as peptogenes. There is, therefore, a remarkable parallelism between the glands of Drosera and those of the stomach in the secretion of their proper acid and ferment. The secretion, as we have seen, completely dissolves albumen, muscle, fibrin, areolar tissue, cartilage, the fibrous basis of bone, gelatin, chondrin, casein in the state in which it exists in n1ilk, and glutPn which has been subjected to weak hydrochloric acid. Syntonin and legumin excite the leaves so powerfully and quickly that there can hardly be a doubt that both would be dissolved by the secretion. The secretion * 'Phys. de la Digestion,' 1867, tom. ii. pp. 188, 245. K |