Page:Popular Science Monthly Volume 8.djvu/66

56 vulgaris, the result being to establish beyond question the predatory practices of the bladderwort, a plant which had hitherto enjoyed a good name.

It is not provided with any irritable filaments, the sensitiveness residing in the surface of the leaf, which is set with two kinds of glandular hairs secreting an extremely viscid fluid which seems to be the only agent for entrapping the insects. When once caught they are detained by the slowly-inflecting leaf. Here, too, contact with nitrogenous bodies changes the nature of the secretion, so that it becomes

capable of dissolving and digesting insects and other nutritious substances, when the secretion and the digested matter are reabsorbed by the glands. When the objects are too large to be inclosed by the inflected leaf, they are by its incurving pushed along over the surface, constantly coming in contact with fresh and hungry glands, subserving the needs of the plants as well as by the other method (see Fig. 8).

Utricularia neglecta and U. vulgaris (common Bladderwort).—It will be a new revelation to most readers to be told that the bladders of this plant are not, as the manuals have always stated, filled with air and intended to float the plant, but that their real use is to capture small aquatic animals, which they do on a large scale.

The general appearance of a bladder is shown in the figure (10) given below. The lower side is straight, the other surface convex and terminating in two long prolongations bearing six or seven long pointed bristles. The prolongations are called antennæ, for, as Mr. Darwin says, "the whole bladder curiously resembles the entomostracean Crustacea" upon which they prey so freely.

Under these antennæ, where the bladder is slightly truncated, is situated the most curious and important part of the whole structure, namely, the entrance and valve.