Insectivorous Plants Part 30
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round the cylinder like a thread round a screw. If the cylinder is now removed, we shall have a tube like one of the spiral arms. The two projecting edges are not actually united, and a needle can be pushed in easily between them. They are indeed in many places a little separated, forming narrow entrances into the tube; but this may be the result of the drying of the specimens. The lamina of which the tube is formed seems to be a lateral prolongation of the lip of the orifice; and the spiral line between the two projecting edges is continuous with the corner of the orifice. If a fine bristle is pushed down one of the arms, it pa.s.ses into the top of the hollow neck. Whether the arms are open or closed at their extremities could not be determined, as all the specimens were broken; nor does it appear that Dr. Warming ascertained this point.
FIG. 29. (Genlisea ornata.) Utriculiferous leaf; enlarged about three times. l Upper part of lamina of leaf. b Utricle or bladder. n Neck of utricle. o Orifice. a Spirally wound arms, with their ends broken off.
So much for the external structure. Internally the lower part of the utricle is covered with spherical papillae, formed of four cells (sometimes eight according to Dr. Warming), which evidently answer to the quadrifid processes within the bladders of Utricularia. [page 448]
These papillae extend a little way up the dorsal and ventral surfaces of the utricle; and a few, according to Warming, may be found in the upper part. This upper region is covered by many transverse rows, one above the other, of short, closely approximate hairs, pointing downwards. These hairs have broad bases, and their tips are formed by a separate cell. They are absent in the lower part of the utricle where the papillae abound.
FIG. 30. (Genlisea ornata.) Portion of inside of neck leading into the utricle, greatly enlarged, showing the downward pointed bristles, and small quadrifid cells or processes.
The neck is likewise lined throughout its whole length with transverse rows of long, thin, transparent hairs, having broad bulbous (fig. 30) bases, with similarly constructed sharp points. They arise from little projecting ridges, formed of rectangular epidermic cells. The hairs vary a little in length, but their points generally extend down to the row next below; so that if the neck is split open and laid flat, the inner surface resembles a paper of pins,--the hairs representing the pins, and the little transverse ridges representing the folds of paper through which the pins are thrust. These rows of hairs are indicated in the previous figure (29) by numerous transverse lines crossing the neck. The inside of the neck is [page 449] also studded with papillae; those in the lower part are spherical and formed of four cells, as in the lower part of the utricle; those in the upper part are formed of two cells, which are much elongated downwards beneath their points of attachment. These two-celled papillae apparently correspond with the bifid process in the upper part of the bladders of Utricularia. The narrow transverse orifice (o, fig. 29) is situated between the bases of the two spiral arms. No valve could be detected here, nor was any such structure seen by Dr. Warming. The lips of the orifice are armed with many short, thick, sharply pointed, somewhat incurved hairs or teeth.
The two projecting edges of the spirally wound lamina, forming the arms, are provided with short incurved hairs or teeth, exactly like those on the lips. These project inwards at right angles to the spiral line of junction between the two edges. The inner surface of the lamina supports two-celled, elongated papillae, resembling those in the upper part of the neck, but differing slightly from them, according to Warming, in their footstalks being formed by prolongations of large epidermic cells; whereas the papillae within the neck rest on small cells sunk amidst the larger ones. These spiral arms form a conspicuous difference between the present genus and Utricularia.
Lastly, there is a bundle of spiral vessels which, running up the lower part of the linear leaf, divides close beneath the utricle. One branch extends up the dorsal and the other up the ventral side of both the utricle and neck. Of these two branches, one enters one spiral arm, and the other branch the other arm.
The utricles contained much dbris or dirty matter, which seemed organic, though no distinct organisms [page 450] could be recognised.
It is, indeed, scarcely possible that any object could enter the small orifice and pa.s.s down the long narrow neck, except a living creature.
Within the necks, however, of some specimens, a worm with retracted h.o.r.n.y jaws, the abdomen of some articulate animal, and specks of dirt, probably the remnants of other minute creatures, were found. Many of the papillae within both the utricles and necks were discoloured, as if they had absorbed matter.
From this description it is sufficiently obvious how Genlisea secures its prey. Small animals entering the narrow orifice--but what induces them to enter is not known any more than in the case of Utricularia--would find their egress rendered difficult by the sharp incurved hairs on the lips, and as soon as they pa.s.sed some way down the neck, it would be scarcely possible for them to return, owing to the many transverse rows of long, straight, downward pointing hairs, together with the ridges from which these project. Such creatures would, therefore, perish either within the neck or utricle; and the quadrifid and bifid papillae would absorb matter from their decayed remains. The transverse rows of hairs are so numerous that they seem superfluous merely for the sake of preventing the escape of prey, and as they are thin and delicate, they probably serve as additional absorbents, in the same manner as the flexible bristles on the infolded margins of the leaves of Aldrovanda. The spiral arms no doubt act as accessory traps. Until fresh leaves are examined, it cannot be told whether the line of junction of the spirally wound lamina is a little open along its whole course, or only in parts, but a small creature which forced its way into the tube at any point, would be prevented from escaping by the incurved hairs, and would find an open path down [page 451] the tube into the neck, and so into the utricle. If the creature perished within the spiral arms, its decaying remains would be absorbed and utilised by the bifid papillae. We thus see that animals are captured by Genlisea, not by means of an elastic valve, as with the foregoing species, but by a contrivance resembling an eel-trap, though more complex.
Genlisea africana (South Africa).--Fragments of the utriculiferous leaves of this species exhibited the same structure as those of Genlisea ornata. A nearly perfect Acarus was found within the utricle or neck of one leaf, but in which of the two was not recorded.
Genlisea aurea (Brazil).--A fragment of the neck of a utricle was lined with transverse rows of hairs, and was furnished with elongated papillae, exactly like those within the neck of Genlisea ornata. It is probable, therefore, that the whole utricle is similarly constructed.
Genlisea filiformis (Bahia, Brazil).--Many leaves were examined and none were found provided with utricles, whereas such leaves were found without difficulty in the three previous species. On the other hand, the rhizomes bear bladders resembling in essential character those on the rhizomes of Utricularia. These bladders are transparent, and very small, viz. Only 1/100 of an inch (.254 mm.) in length. The antennae are not united at their bases, and apparently bear some long hairs. On the outside of the bladders there are only a few papillae, and internally very few quadrifid processes. These latter, however, are of unusually large size, relatively to the bladder, with the four divergent arms of equal length. No prey could be seen within these minute bladders. As the rhizomes of this species were furnished with bladders, those of Genlisea africana, ornata, and aurea were carefully [page 452] examined, but none could be found. What are we to infer from these facts? Did the three species just named, like their close allies, the several species of Utricularia, aboriginally possess bladders on their rhizomes, which they afterwards lost, acquiring in their place utriculiferous leaves? In support of this view it may be urged that the bladders of Genlisea filiformis appear from their small size and from the fewness of their quadrifid processes to be tending towards abortion; but why has not this species acquired utriculiferous leaves, like its congeners?
CONCLUSION.--It has now been shown that many species of Utricularia and of two closely allied genera, inhabiting the most distant parts of the world--Europe, Africa, India, the Malay Archipelago, Australia, North and South America--are admirably adapted for capturing by two methods small aquatic or terrestrial animals, and that they absorb the products of their decay.
Ordinary plants of the higher cla.s.ses procure the requisite inorganic elements from the soil by means of their roots, and absorb carbonic acid from the atmosphere by means of their leaves and stems. But we have seen in a previous part of this work that there is a cla.s.s of plants which digest and afterwards absorb animal matter, namely, all the Droseraceae, Pinguicula, and, as discovered by Dr. Hooker, Nepenthes, and to this cla.s.s other species will almost certainly soon be added. These plants can dissolve matter out of certain vegetable substances, such as pollen, seeds, and bits of leaves. No doubt their glands likewise absorb the salts of ammonia brought to them by the rain. It has also been shown that some other plants can absorb ammonia by [page 453] their glandular hairs; and these will profit by that brought to them by the rain. There is a second cla.s.s of plants which, as we have just seen, cannot digest, but absorb the products of the decay of the animals which they capture, namely, Utricularia and its close allies; and from the excellent observations of Dr. Mellichamp and Dr. Canby, there can scarcely be a doubt that Sarracenia and Darlingtonia may be added to this cla.s.s, though the fact can hardly be considered as yet fully proved. There is a third cla.s.s of plants which feed, as is now generally admitted, on the products of the decay of vegetable matter, such as the bird's-nest orchis (Neottia), &c. Lastly, there is the well-known fourth cla.s.s of parasites (such as the mistletoe), which are nourished by the juices of living plants. Most, however, of the plants belonging to these four cla.s.ses obtain part of their carbon, like ordinary species, from the atmosphere. Such are the diversified means, as far as at present known, by which higher plants gain their subsistence.
Insectivorous Plants Part 30
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Insectivorous Plants Part 30 summary
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