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Show 230 DROSERA ROTUNDIFOLIA. CHAP. X. It is probable that they were killed so instantly that they were not able to transmit any motor impulse; for in six observed cases (in two of which however the gland was quite pinched off) the protoplasm within the cells of the tentacles did not become aggregated; whereas in some adjoining tentacles, which were inflected from having been roughly touched by the pincers, it was well aggregated. In like manner the protoplasm does not become aggregated when a leaf is instantly killed by being clipped into boiling water. On the other hand, in several cases in which tentacles became inflected after their glands had been cut off with sharp scissors, a distinct though moderate degree of aggregation supervened. The pedicels of the tentacles were roughly and repeatedly rubbed; raw meat or other exciting substances were placed on them, both on the upper surface near the base and elsewhere, but no distinct movement ensued. Some bits of meat, after being left for a considerable time on the pcdicels, were pushed upwards, so as just to touch the glands, and in a minute the tentacles began to bend. I believe that the blade of the leaf is not sensitive to any stimulant. I drove the point of a lancet through the blades of several leaves, and a needle three or four ti1nes through nineteen leaves : in the former case no movement ensued; but about a dozen of the leaves which were repeatedly pricked had a few tentacles irregulady inflected. As, however, their backs had to be supported during the operation, some of the outer glands, as well as those on the disc, may have been touched; and this perhaps sufficed to cause the slight degree of move1nent observed. Nitschke* says * 'Bot. Zeitung,' 1860, p. 234. CHAP. X. SENSITIVENESS OF THE LEAVES. 231 that cutting and pricking the leaf does not excite movement. The petiole of the leaf is quite insensible. The backs of the leaves bear numerous minute papillre, which do not secrete, but have the power of absorption. These papillre are, I believe, rudiments of formerly existing tentacles together with their glands. Many experiments were made to ascertain whether the backs of the leaves could be irritated in any way, thirty-seven leaves being thus tried. Some were rubbed for a long time with a blunt needle, and drops of milk and other exciting fluids, raw meat, crushed flies, and various substances, placed on others. These substances were apt soon to become dry, showing that no secretion had been excited. Hence I moistened them with saliva, solutions of ammonia, weak hydrochloric acid, and frequently with the secretion from the glands of other leaves. I also kept some leaves, on the backs of which exciting objects had been placed, under a damp bell-glass; but with all my care I never saw any true movement. I was led to make so many trials because, contrary to my previous experience, Nitschke states* that, after affixing objects to the backs of leaves by the aid of the viscid secretion, he repeatedly saw the tentacles (and in one instance the blade) become reflex eel. This movement, if a true one, would be most anonlalous; for it implies that the tentacles receive a motor impulse from an unnatural source, and have the power of bending in a direction exactly the reverse of that which is habitual to them; this power not being of the least use to the plant, as insects cannot adhere to the smooth backs of the leaves. I have said that no effect was produced in the abov * 'Bot. Zeitung,' 1860, p. 437. |