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Show 126 DROSERA ROTUNDIFOLIA. 0II.AP. VI. used as well as some freshly prepared, with artificial digestive liquid, and found that it was not digested. D~. La"?-dor BruJ?-ton likewise tried some prepared by the process given In the Bntish Pharmacopceia, and expose~ i~ for fiv~ days at the _tel?l?eratu~e of 37° Cent. to digestive hqmd, but It was not diminished m bulk, though the fluid acquired a slightly brown c?lour. It ~as also tried with the glycerine extract of pancreas with a negative result. Nor does chlorophyll seem affected by the intestinal secretions of various animals, judging by the colour of their excrement. It must not be supposed from these facts that the grains of chlorophyll, as they exist in living plants, cannot be attacked by the secretion; for these grains consist of protoplasm merely coloured by chlorophyll. My son Francis placed a thin slice of spinach leaf, moistened with saliva, on a leaf of Drosora, and other slices on damp cotton-wool, all exposed to the t:ame temperature. After 19 hrs. the slice on the loaf of Drosera was bathed in much secretion from the inflected tentacles, and was now examined under the microscope. No perfect grains of chlorophyll could be distinguished ; some were shrunken, of a yellowish-green colour, and collected in the middle of the cells; others were disintegrated and formed a yellowish mass, likewise in the middle of the cells. On ·the other hand, in the slices surrounded by damp cotton-wool, the grains of chlorophyll were green and as perfect as ever. My son also placed some slices in artificial gastric juice, and these were acted on in nearly the same manner as by the secretion. We have seen that bits of fresh cabbage and spinach leaves cause the tentacles to be inflected and the glands to pour forth much acid secretion ; and there can be little doubt that it is the protoplasm forming the grains of chlorophyll, as well as that lining the walls of the cells, which excites the leaves. Pat and Oil.-Cubes of almost pure uncooked fat, placed on several leaves, did not have their angles in the least rounded. We have also seen that the oil-globules in milk are not digested. Nor does olive oil dropped on the discs of leaves cause any inflection; but when they are immersed in olive oil, they become strongly inflected; but to this subject I shall have to recur. Oily substances are not digested by the gastric juice of animals. Starch.-Rather large bits of dry starch caused well-marked inflection, and the leaves did not re-expand until the fourth day; but I have no doubt that this was due to the prolonged irritation of the glands, as the starch continued to absorb the secretion. The particles were not in the least reduced in size; CHAP. VI. DIGESTION. 127 and we know that leaves immersed in an emulsion of starch a~e not at all affect~d .. ! need hardly say that starch is not digested by the gastnc JUice of animals. Action of the Secret£on on Living Seeds. The results of some experiments on living seeds selected b hazard, may here be given, though they bear only i~directly 0~ our present subject of digestion. Seven cabbage seeds of the previous year were placed on the same number of leaves. Some of these leaves were moderate! but the greater number only slightly inflected, and most ~t· them re-~xpanded on the third day. One, however, remained clasped till the fourth, ~nd another till the fifth day. These lea:es ther~fore _were exmted somewhat more by the seeds than by Inorgamc obJects of the same size. After they re-expanded the seeds were placed under favourable conditions on dam' ~and; other seeds of the same lot being tried at the same tim~ In the sa~e manner, and found to germinate well. Of the seven se~ds W~ICh had been exposed to th~ secretion, only three germn~ ated, ~nd on~ of the three seedlmgs soon perished, the tip ?f ItS radicle bmng from the first decayed, and the edges of Its cotyledons of a dark ?rown colour; so that altogether five out of_ the seven seeds ultimately perished. Radish seeds (Baphanus sativus) of the previous year were placed on three leaves, which became moderately inflected and re-expanded on the third or fourth day. Two of these ~eeds were transferred ~o dam~ sand; only one germinated, and that v~ry slowly .. . This. seedlmg had an extremely short, crooked, diseased, radicle, With_ no absorbent hairs; and the cotyledons were od?ly mottled With purple, with the edges blackened and partly withered. Cress seeds ( Lepidum sativum) of the previous year were placed on four leaves ; two of these next morning were moderately and two. strongly inflected, and remained so for four, five, and e-ven SJX days. Soon after these seeds were placed on the leaves and had become damp, they secreted in the usual ~anner a layer of tenacious mucus; and to ascertain whether It was the absorption of this substance by the glands which caused so much inflection, two seeds were put into water, and as much of the mu01~s as possible scraped off. They were then placed on leaves, whiCh became very strongJy inflected in the course of 3 h.rs., ~nd were still closely inflected on the third day; so ~hat It evidently was not the mucus which excited so |