If an insect is placed on the central glands, or has been naturally caught there, the apex of the leaf curls inwards. For instance, dead flies were placed on three leaves near their bases, and after 24 hrs. the previously straight apices were curled completely over, so as to embrace and conceal the flies; they had therefore moved through an angle of 180o. After three days the apex of one leaf, together with the tentacles, began to re-expand. But as far as I have seen— and I made many trials—the sides of the leaf are never inflected, and this is the one functional difference between this species and Drosera rotundifolia.
Drosera intermedia (Hayne).—This species is quite as common in some parts of England as Drosera rotundifolia. It differs from Drosera anglica, as far as the leaves are concerned, only in their smaller size, and in their tips being generally a little reflexed. They capture a large number of insects. The tentacles are excited into movement by all the causes above specified; and aggregation ensues, with movement of the protoplasmic masses. I have seen, through a lens, a tentacle beginning to bend in less than a minute after a particle of raw meat had been placed on the gland. The apex of the leaf curls over an exciting object as in the case of Drosera anglica. Acid secretion is copiously poured over captured insects. A leaf which had embraced a fly with all its tentacles re-expanded after nearly three days.
Drosera capensis.—This species, a native of the Cape of Good Hope, was sent to me by Dr. Hooker. The leaves are elongated, slightly concave along the middle and taper towards the apex, [page 280] which is bluntly pointed and reflexed. They rise from an almost woody axis, and their greatest peculiarity consists in their foliaceous green footstalks, which are almost as broad and even longer than the gland-bearing blade. This species, therefore, probably draws more nourishment from the air, and less from captured insects, than the other species of the genus. Nevertheless, the tentacles are crowded together on the disc, and are extremely numerous; those on the margins being much longer than the central ones. All the glands have the same form; their secretion is extremely viscid and acid.
The specimen which I examined had only just recovered from a weak state of health. This may account for the tentacles moving very slowly when particles of meat were placed on the glands, and perhaps for my never succeeding in causing any movement by repeatedly touching them with a needle. But with all the species of the genus this latter stimulus is the least effective of any. Particles of glass, cork, and coal-cinders, were placed on the glands of six tentacles; and one alone moved after an interval of 2 hrs. 30 m. Nevertheless, two glands were extremely sensitive to very small doses of the nitrate of ammonia, namely to about 1/20 of a minim of a solution (one part to 5250 of water), containing only 1/115200 of a grain