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Show 204 DION lEA MUSCIPULA. CHAP. XIII. between the lobes, one re-expanded after two days; a second after seven days; and the third after nine days. The leaf which closed, owing to a drop of the solution having adhered to one of the filaments, opened after two days. I was surprised to find on two occasions that the heat fro1n the rays of the sun, concentrated by a lens on the bases of several :filaments, so that they wore scorched and discoloured, did not cause any movoInent; though the leaves were active, as they closed, though rather slowly, when a filament on the opposite side was touched. On a third trial, a fresh leaf closed after a time, though very slowly; the rate not being increased by one of the fila1nents, which had not Loen injured, being touched. After a day these three leaves opened, and were fairly sensitive when the uninjureu fila1nents were touched. The sudden immersion of a leaf into boiling water does not cause it to close. Judging from the analogy of Drosera, the heat in these several cases was too great and too suduenl y applied. The surface of the blade is very slightly sensitive ; it may be freely and roughly handled, without any movement being caused. A leaf was scratcheu rather hard with a needle, but did not close; but when the triangular space between the three filaments on another leaf was similarly scratched, the lobes closed. They always closed when the blade or midrib was deeply pricked or cut. Inorganic bodies, even of large size, such as bits of stone, glass, &c.-or organic bodies not containing soluble nitrogenous matter, such as bits of wood, cork, moss,- or bodies containing soluble nitrogenous matter, if perfectly dry, such as bits of 1neat, albumen, gelatine, &c., may be long left (and many were tried) on the lobes, and no movement is excited. The result, however, is widely different, as we CHAP. XIII. SECRETION AND ABSORPTION. 295 shall pres en tl y see, if nitrogenous organic bodies which are at all damp, are left on the lobes; for these then close by a slow and gradual movement, very different from that caused by touching one of the sensitive filaments. The footstalk is not in the least sensitive; a pin may be driven through· it, or it may be cut off~ and no moven1en t follows. ~rhe upper surface of the lobes, as already stated, is thickly covered with small purplish, almost sessile glands. These have the power both of secretion and absorption; but unlike those of Drosera, they do not secrete until excited by the absorption of nitrogenous matter. No other excitement, as far as I have seen, produces this effect. Objects, such as bits of wood, cork, moss, paper, stone, or glass, may be left for a length of time on the surface of a leaf, and it remains quite dry. Nor does it make any difference if the lobes close over such objects. For instance, some little balls of blotting paper were placed on a leaf, and a filament was touched; and when after 24 hrs. the lobes began to re-open, the balls were removed by the aid of thin pincers, and were found perfectly dry. On the other hand, if a bit of damp meat or a crushed fly is placed on the surface of an expanded leaf, the glands after a time secrete freely. In one such case there was a little secretion directly beneath the 1neat in 4 hrs.; and after an additional 3 hrs. there was a considerable quantity both under and close round it. In another case, after 3 hrs. 40 m., the bit of meat vvas quite wet. But none of the glands secreted, excepting those .which actually touched the meat or the secretion containing dissolved animal matter. If, however, the lobes are made to close over a bit of meat or an insect, the result is different, for the glands over the whole surface of the leaf now secrete copiously. |