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Show 280 DROSERA SP ATHULATA. CHAP. XII. which is bluntly pointed and reflexed. They rise from an almost woody axis, and their greate~t peculiarit! consists in their foliaceous green footstalks, whiCh are almo~G as b~oad and ~ven longer than the gland-bearing blade. This specws, therefore, probably draws more nourishment fr?m the air, and less from captured insects, than the other spomes of the gen~s. Nevertheless the tentacles are crowded together on tho disc, and are extrem'ely 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. '.rhe 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. 30m. Nevertheless, two glands were extremely sensitive to very small doses of the nitrate of ammonia, namely to about 21s of a minim of a solution (one part to 5250 of water), containing only n s\oo of a grain ('000562 mg.) of the salt. Fragments of flies were placed on two leaves ncar their tips, which became incurved in 15 hrs. A fly was also placed in the middle of the leaf; in a few hours the tentacles on each side embraced it, and in 8 hrs. the whole leaf directly beneath the fly was a little bent transversely. By the next morning, after 23 hrs., the leaf was curled so completely over that the apex rested on the upper end of tho footstalk. In no case did the sides of the leaves become inflected. A crushed fly was placed on the foliaceous footstalk, but produced no effect. Drosera spathulata (sent to me by Dr. Hooker).-I made only a few observations on this Australian species, which has long, narrow leaves, gradually widening towards their tips. The glands of the extreme marginal tentacles are elongated and differ from the others, as in the case of Drosera rotund1jotia. A fly was placed on a leaf, and in 18 hrs. it was embraced by the adjoining tentacles. Gum-water dropped on several leaves produced no effect. A fragment of a leaf was immersed in a few drops of a solution of one part of carbonate of ammonia to 146 of water; all the glands were instantly blackened ; the procf:;)ss of aggregation could be seen tra veiling rapidly down the cells of the tentacles; and the granules of protoplasm soon united into spheres and variously shaped masses, which displayed the usual move- CHAP. XII. DROSERA FILIFORMIS. 281 ments. Half a minim of a solution of one part of nitrate of ammonia to 146 of water was next placed on the centre of a leaf; after 6 hrs. some marginal te~ tacles on both sides were inflected, and after 9 hrs. they met in the centre. The lateral edges of the leaf also became incurved, so that it formed a half-cylinder; but the apex of the leaf in none of my few trials was inflected. The above dose of the nitrate (viz. 3 -hJ of a grain, or ·202 mg.) was too powerful, for in the course of 23 hrs. the leaf died. Drosera jU1jormis.-This North American species grows in such abundance in parts of New Jersey as almost to cover the ground. It catches, according to Mrs. Treat,* an extraordinary number of small and large insects,-even great flies of the genus Asilus, moths, and butterflies. The specimen which I examined, sent me by Dr. Hooker, had thread-like leaves, from 6 to 12 inches in length, with the upper surface convex and the lower flat and sUghtly channelled. The whole convex surface, down to the roots-for there is no distinct footstalk-is covered with short gland-bearing tentacles, those on the margins being the longest and reflexed. Bits of meat placed on the glands of some tentacles caused them to be slightly inflected in 20 m. ; but the plant was not in· a vigorous state. After 6 hrs. they moved through an angle of 90°, and in 24 hrs. reached the centre. The surrounding tentacles by this time began to curve inwards. Ultimately a large drop of extremely viscid, slightly acid secretion was poured over the meat from the united glands. Several other glands were temched with a little saliva, and the tentacles became incurved in under 1 hr., and re-expanded after 18 hrs. Particles of glass, cork, cinders, thread, and gold-leaf, were placed on numerous glands on two leaves; in about 1 hr. four tentacles became curved, and four others after an additional interval of 2 hrs. 30m. I never once succeeded in causing any movement by repeatedly touching the glands with a needle; and Mrs. Treat made similar trials for me with no success. Small flies were placed on several leaves near their tips, but the thread-like blade became only on one occasion very slightly bent, directly beneath the insect. Perhaps this indicates that the blades of vigorous plants would bend over captured insects, and Dr. Canby informs me that this is the case; but the movement cannot be strongly pronounced, as it was not observed by Mrs. Treat. Drosera binata (or dichotoma).-1 am much indebted to Lady * ' American N atw·alist,' Dec. 1873, p. 705. |