OCR Text |
Show 116 DROSERA RO'l'UNDIFOLIA. CnAP. VI. a non-albuminous, substance; and the absorption of a very small quantity of the former would excite the leaves, and yet not decrease the casein to a perceptible degree. Schiff assorts*-and this is an important fact for us-that "la caseine puri:fiee des chimistes est un corps presque completement inattaquable par le sue gastrique." So that here we have another point of accordance between the secretion of Drosera and gastric juice, as both act so differently on the fresh casein of milk, and on that prepared by cheinists. A few trials were Inade with cheese; cuLos of c} 0 of an inch (1·27 n1m.) were placeu on four leaves, and these after one or two days became well inflected, their glands pouring forth much acid secretion. ... AJter :five days they began to re-expand, but one died, and some of the glands on the other leaves were injured. Judging by the eye, the softened and subs~ ded masses of cheese, left on the discs, were very httle or not at all reduced in bulk. We may, however, infer from the time during which tho tentacles remained inflected,-from the changed colour of so1ne of the glands,-and from the injury don to others, that 1natter had been absorbed from tho cheese. Legumin.-! did not procure this substance in a separate state ; but there can hardly be a doubt that j t would be easily digested, judging from the powerful effect produced by drops of a decoction of green peas, as described in the last chapter. Thin slices of a dried pea, after being soaked in water, were placed on two leaves; these became somewhat inflected in ;he course of a single hour, and most strongly so in 21 hrs. They re-expanded after three or four days. . * 'Le<;ons,' &c. tom. ii. p. 153. CHAP. VI. DIGESTION. 117 The slices were not liquefied, for the walls of the cells com posed of cellulose, are not in the least acted on' by the secretion. Pollen.-A little fresh pollen from the common !)ea was placed on the discs of :five leaves, which soon became closely inflecteu, and remained so for two or three days. The grains being then removed, and examined under the microscope, were found discoloured, with the oilglobules remarkably aggregated. Many had their contents much shrunk, and some were almost empty. In only a few cases were the pollen-tubes emitto(l. There could .be no doubt that the secretion had penetrated the otiter coats of the grains, and had partially digested their contents. So it must be with the gastric juice of the insects which food on pollen, without masticating it.* Drosera in a state of nature cannot fail to profit to a certain extent by this power of digesting pollen, as innumerable grains fron1 the oarices, grasses, rumices, fir-trees, and other windfertilised plants, which comn1only grow in the san1e neighbourhood, will be inevitably caught by the visci<l secretion surrounding the many glands. Gluten.-This substance is composed of two albuminoids, one soluble, the other insoluble in alcohol.t Some was prepared by merely ~ashing wheaten flour in water. A provisional trial was made with rather large pieces placed on two leaves; these, after 21 hrs., were closely inflected, and remained so for four days, when one was killed and the other had its glands extremely blackened, but was not afterwards observe(l. * Mr. A. W. Bennett found the undigested coats of the grains in the intestinal canal of polleneating Diptera; see 'Journal of Hort. Soc. of London,' vol. iv. 1874, p. 158. t Watt::;' 'Diet. of Chemi try,' vol. ii. 1872, p. 873. . |