Digestion of Solid Animal Matter.—Whilst I was trying to place on two of the taller glands little cubes of albumen, these slipped down, and, besmeared with secretion, were left resting on some of the small sessile glands. After 24 hrs. one of these cubes was found [page 340] completely liquefied, but with a few white streaks still visible; the other was much rounded, but not quite dissolved. Two other cubes were left on tall glands for 2 hrs. 45 m., by which time all the secretion was absorbed; but they were not perceptibly acted on, though no doubt some slight amount of animal matter had been absorbed from them. They were then placed on the small sessile glands, which being thus stimulated secreted copiously in the course of 7 hrs. One of these cubes was much liquefied within this short time; and both were completely liquefied after 21 hrs. 15 m.; the little liquid masses, however, still showing some white streaks. These streaks disappeared after an additional period of 6 hrs. 30 m.; and by next morning (i.e. 48 hrs. from the time when the cubes were first placed on the glands) the liquefied matter was wholly absorbed. A cube of albumen was left on another tall gland, which first absorbed the secretion and after 24 hrs. poured forth a fresh supply. This cube, now surrounded by secretion, was left on the gland for an additional 24 hrs., but was very little, if at all, acted on. We may, therefore, conclude, either that the secretion from the tall glands has little power of digestion, though strongly acid, or that the amount poured forth from a single gland is insufficient to dissolve a particle of albumen which within the same time would have been dissolved by the secretion from several of the small sessile glands. Owing to the death of my last plant, I was unable to ascertain which of these alternatives is the true one.
Four minute shreds of pure fibrin were placed, each resting on one, two, or three of the taller glands. In the course of 2 hrs. 30 m. the secretion was all absorbed, and the shreds were left almost dry. They [page 341] were then pushed on to the sessile glands. One shred, after 2 hrs. 30 m., seemed quite dissolved, but this may have been a mistake. A second, when examined after 17 hrs. 25 m., was liquefied, but the liquid as seen under the microscope still contained floating granules of fibrin. The other two shreds were completely liquefied after 21 hrs. 30 m.; but in one of the drops a very few granules could still be detected. These, however, were dissolved after an additional interval of 6 hrs. 30 m.; and the surface of the leaf for some distance all round was covered with limpid fluid. It thus appears that Drosophyllum digests albumen and fibrin rather more quickly than Drosera can; and this may perhaps be attributed to the acid, together probably with some small amount of the ferment, being present in the secretion, before the glands have been stimulated; so that digestion begins at once.
Concluding Remarks.—The linear leaves of Drosophyllum differ but slightly from those of certain species of Drosera; the chief differences being, firstly, the presence of minute, almost sessile, glands, which, like those of Dionaea, do not secrete until they are excited by the absorption of nitrogenous matter. But glands of this kind are present on the leaves of Drosera binata, and appear to be represented by the papillae on the leaves of Drosera rotundifolia. Secondly, the presence of tentacles on the backs of the leaves; but we have seen that a few tentacles, irregularly placed and tending towards abortion, are retained on the backs of the leaves of Drosera binata. There are greater differences in function between the two genera. The most important one is that the tentacles of Drosophyllum have no power of movement; this loss being partially replaced by the drops of viscid [page 342] secretion being readily withdrawn from the glands; so that, when an insect comes into contact with a drop, it is able to crawl away, but soon touches other drops, and then, smothered by the secretion, sinks down on the sessile glands and dies. Another difference is, that the secretion from the tall glands, before they have been in any way excited, is strongly acid, and perhaps contains a small quantity of the proper ferment. Again, these glands do not secrete more copiously from being excited by the absorption of nitrogenous matter; on the contrary, they then absorb their own secretion with extraordinary quickness. In a short time they begin to secrete again. All these circumstances are probably connected with the fact that insects do not commonly adhere to the glands with which they first come into contact, though this does sometimes occur; and that it is chiefly the secretion from the sessile glands which dissolves animal matter out of their bodies.
RORIDULA.
Roridula dentata.—This plant, a native of the western parts of the Cape of Good Hope, was sent to me in a dried state from Kew. It has an almost woody stem and branches, and apparently grows to a height of some feet. The leaves are linear, with their summits much attenuated. Their upper and lower surfaces are concave, with a ridge in the middle, and both are covered with tentacles, which differ greatly in length; some being very long, especially those on the tips of the leaves, and some very short. The glands also differ much in size and are somewhat elongated. They are supported on multicellular pedicels.
This plant, therefore, agrees in several respects with [page 343] Drosophyllum, but differs in the following points. I could detect no sessile glands; nor would these have been of any use, as the upper surface of the leaves is thickly clothed with pointed, unicellular hairs directed upwards. The pedicels of the tentacles do not include spiral vessels; nor are there any spiral cells within the glands. The leaves often arise in tufts and are pinnatifid, the divisions projecting at right angles to the main linear blade. These lateral divisions are often very short and bear only a single terminal tentacle, with one or two short ones on the sides. No distinct line of demarcation can be drawn between the pedicels of the long terminal tentacles and the much attenuated summits of the leaves. We may, indeed, arbitrarily fix on the point to which the spiral vessels proceeding from the blade extend; but there is no other distinction.
It was evident from the many particles of dirt sticking to the glands that they secrete much viscid matter. A large number of insects of many kinds also adhered to the leaves. I could nowhere discover any signs of the tentacles having been inflected over the captured insects; and this probably would have been seen even in the dried specimens, had they possessed the power of movement. Hence, in this negative character, Roridula resembles its northern representative, Drosophyllum.
BYBLIS.
Byblis gigantea (Western Australia).—A dried specimen, about 18 inches in height, with a strong stem, was sent me from Kew. The leaves are some inches in length, linear, slightly flattened, with a small projecting rib on the lower surface. They are covered on all sides by glands of two kinds [page 344] —sessile ones arranged in rows, and others supported on moderately long pedicels. Towards the narrow summits of the leaves the pedicels are longer than elsewhere, and here equal the diameter of the leaf. The glands are purplish, much flattened, and formed of a single layer of radiating cells, which in the larger glands are from forty to fifty in number. The pedicels consist of single elongated cells, with colourless, extremely delicate walls, marked with the finest intersecting spiral lines. Whether these lines are the result of contraction from the drying of the walls, I do not know, but the whole pedicel was often spirally rolled up. These glandular hairs are far more simple in structure than the so-called tentacles of the preceding genera, and they do not differ essentially from those borne by innumerable other plants. The flower-peduncles bear similar glands. The most singular character about the leaves is that the apex is enlarged into a little knob, covered with glands, and about a third broader than the adjoining part of the attenuated leaf. In two places dead flies adhered to the glands. As no instance is known of unicellular structures having any power of movement,* Byblis, no doubt, catches insects solely by the aid of its viscid secretion. These probably sink down besmeared with the secretion and rest on the small sessile glands, which, if we may judge by the analogy of Drosophyllum, then pour forth their secretion and afterwards absorb the digested matter.
Supplementary Observations on the Power of Absorption by the Glandular Hairs of other Plants.—A few observations on this subject may be here conveniently introduced. As the glands of many, probably of all,