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Show 380 PINGUICULA VULGARIS. CHAP. XVI: Prof. Dyer, in most or all the species of the genus, the edges of the leaves are in so1ne degree naturally and permanently incurved. This incurvation serves, as ah·ead y shown, to prevent insects from being washed away by the rain ; but it likewise serves for another end. When a number of glands have been powerfully excited by bits of meat, insects, or any other stimulus, the secretion often trickles down the leaf, and is caught by the incurvod edges, instead of rolling off and being lost. As it runs down the channel, fresh glands are able to absorb the animal matter held in solution. Moreover, the secretion often collects in little pools within the channel, or in the spoon-like tips of the leaves; and I ascertained that bits of albumen, :fibrin, and gluten, are here dissolved more quickly and completely than on the surface of the leaf, where the secretion cannot accumulate; and so it would be with naturally caught insects. The secretion was repeatedly seen thus to colle.ct on the leaves of plants protected from the rain; and with exposed plants there would be still greater need of some provision to prevent, as far as possible, the secretion, with its dissolved animal matter, being wholly lost. It has already been remarked that plants growing in a state of nature have the 1nargins of their leaves much more strongly incurved than those grown in pots and prevented from catching many insects. We have seen that insects wash d down by the rain from all parts of the leaf often lodge within the margins, which are thus excited to curl farther inwards; and we may suspect that this action, many times repeated during the life of the plant, leads to their permanent and well-marked incurvation. I regret that this view did not occur to me in time to test its truth. It may here be added, though not immediately CHAP. XVI. SECRETION, ABSORPTION, DIGESTION. 381 bearing on our subject, that when a plant is pulled up, the leaves immediately curl downwards so as almost to conceal the roots,-a fact which has b 11 noticed by many persons. I suppose that this is du to the same tendency which causes the outer and old leaves to lie flat on the ground. It further appea;: that the flower-stalks are to a certain extent irritabl for Dr. Johnson states that they "bend backwards if' rudely handled." * Secretion, ~bsorption, and. Digestion.-! will first giv n1y observations and expernnents, and then a summary of the results. The EjJeGts of Ob}er:ts containing Soluble Nitrogenous Mutter. (1) Flies w.ere placed on ma~y leaves, and excited the glands to secrete copwusly; the secretwn always becomino- acid tho h t b ~ A . o , ug no so e1ore. fter a time these insects were rendered tender that th~ir limbs and bodies .coul~ be separated by 8~ mere t.ouch, owing no doubt to .the digestwn and disintegration o~ thmr muscles. The glands In contact with a small fiy contmued to secrete for four days, and then became almost dry A narrow strip of this leaf was cut off. and the glands of th~ longer and ~horter hairs, which had lain in contact for the four days With the fly, and those which had not touched it were compared under the microscope and presented a won~ d~rful contr.ast. Those which had been in contact were filled WI~h brownish granular matter, the others with homogeneous fluid. There could therefore be no doubt that the former had absorbed matter from the fly. (2) Small bits of roast meat, placed on a leaf always caused m?c~ acid secretion in the course of a few hou~s-in one case withi~ 40 m. vVhe.n thin fibres of meat were laid along the margin of a leaf which stood almost upright, the secretion ran down to the ground. Angular bits of meat, placed jn little pools of the secretion rlear the margin, were in the course of *' ' English Botany,' by Sir J. E. Smith ; with coloured figm·es by J. ~owcrby ; edit. of 1832, tab. 24, 25, 26. |