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Show 388 PINGUICULA VULGARIS. CHAP. XVI. fluid; and it particularly deserves notice that this, as on the former occasion, was not in the least acid. This great amount of secretion may be attributed to exosmose. The glands which had been covered for 24 hrs. by this fluid did not differ, wben examined under the microscope, from others on the same leaf which bad not come into contact with it. This is an interestin~ fact in contrast with the invariably aggregated condition of glands which have been bathed by the secretion, when holding animal matter in solution. (18) Two particles of ,qurn arabic were placed on a leaf, and they certainly caused in 1 hr. 20m. a slight increase of secretion. This continued to increase for the next 5 hrs., that is for as long a time as tho leaf was observed. (19) Six small particles of dry starch of commerce were placed on a leaf, and one of these aaused some secretion in 1 hr. 15m., and the others in from 8 hrs. to 9 hrs. The glands which had t,hus been excited to secrete soon became dry, and did not begin to secrete again until the sixth day. A larger bit of starch was then placed on a leaf, and no secretion was excited in 5 hrs. 30 m.; but after 8 hrs. there was a considerable supply, which increased so much in 24 hrs. as to run down the leaf to the distance of i of an inch. This secretion, though so abundant; was not in the least acid. As it was so copiously excited, and as seeds not rarely adhere to the leaves of naturally growing plants, it occurred to me that the glands might perhaps have the power of secreting a ferment, like ptyaline, capable of dissolving starch; so I carefully observed the above six small particles during several days, but they did not seem in the least reduced in bulk. A particle was also left for two days in a little pool of secretion, which had run down from a piece of spin~ch leaf; but although the particle was so minute no diminution was perceptible. We may therefore conclude that the secretion cannot dissolve starch. The increase caused by this substance may, I presume, be attributed to exosmose. But I am surprised that starch acted so quickly and powerfully as it did, though in a less degree than sugar. Colloids arc known to possess some slight power of dialysis; and on placing the leaves of a Primula in water, and others in syrup and diffused starch, those in the starch became flaccid, but to a less degree and at a much slower rate than the leaves in the syrup; those in water remaining all the time crisp. From the foregoing experiments and observations we CHAP. XVI. SECRETION, ABSORPTION, DIGESTION. 389 s~e that objects not containing soluble matter have h ttle o. r no power of exciting the gl ancl s t o secrete. Non-nitrogenous fluids, if dense, cause the glands t pour. forth a large supply of viscid fluid, but this i. n_ot In the least acid. On the other hand, the secretio~ from ?la~ds. e~cited. by contact with nitrogenous sohds. or hquids Is Invanably acid, and is so copious t~at. It often runs down the leaves and collects w. ithi.n thh'e naturally incurved margins. The secr.e _ tion I~ t Is s~ate ~as the power of quickly dissolving, that IS of digesting, the muscles of insects meat cartilage, albumen, fibrin, gelatine, and ca~ein a~ it exists in. the curds of milk. The glands are strongly excited by chemically prepared casein and gluten; but t~ese substances (the' latter not having bee~ soake~ In weak hydrochloric acid) are only partially dissolved, as was likewise the case with Drosera.. The ~ecretion, when containing animal matter In solution, whether derived from solids or from liquids, such as an infusion of raw meat milk, or a weak solution of carbonate of ammonia' is quickly absorbed; and the glands, which wer~ before limpid and of a greenish colour, become brownish and contain masses of aggregated granular matter. This rna tter, from its spontaneous movements no doubt consists of protoplasm. No such effect is 'produced by the action of non-nitrogenous fluids. After the glands. have been excited to secrete freely, they cease for a time to secrete, but begin again in the course of a few days. Glands in contact with pollen, the leaves of other pl~nts, and various kinds of seeds, pour forth much acid secretion, and afterwards absorb matter probably of an albuminous nature from them. Nor can the benefit thus derived be insignificant, for a considerable |