Fig. 416.—Diagram of Reseda odorata.
Order 2. Droseraceæ (Sundews). Herbs, chiefly living on moors or in water, and whose leaves are adapted to catch and digest small animals. With regard to the flower, they are closely allied to the Violaceæ, especially to those with regular flowers. Drosera (Sundew) has a long-stalked scorpioid cyme with regular, ☿, hypogynous flowers, 5-merous as in Viola. S5, P5, A5, G3 (in a syncarpous gynœceum, with free, bifid styles and basal or parietally-placed ovules in the unilocular ovaries). The capsule opens also as in Viola, but, among other differences, the styles are free, the seeds very small, and surrounded by a loosely lying, thin shell. Drosera has radical, long-stalked leaves with the blade (Fig. [417]) covered by numerous strong glandular hairs, placed on the edge and in the middle; when small animals are caught by these hairs, the latter and the entire blade close slowly over them dissolving and absorbing all the digestible matter as nourishment.
Fig. 417.—Leaf-rosette of Drosera rotundifolia (nat. size), and a leaf (magnified).
Dionæa muscipula (Fly-trap; N. Am.) has the same appearance as Drosera, but the leaves are constructed as in Fig. [418]. The stalk is flat and winged, the blade small, circular, with powerful, pointed teeth along the edge, and on its surface are 6 small bristles (A), which are very sensitive. When these are touched the blade quickly closes, folding along the midrib (B, C) and imprisoning the irritating object, the teeth round the edges fitting like the teeth of a trap. If it happens to be an insect or similar body, a digestive fluid is secreted which, like the gastric juice, dissolves the digestible portions. Aldrovandia vesiculosa (Central and S. Europe) captures small aquatic animals in a similar manner; it is a floating, aquatic plant, the two halves of its leaves also close together when irritated (Fig. [419]).—Drosophyllum.
About 110 species; most of them in the temperate regions.
Fig. 418.—Dionæa muscipula. Leaves (nat. size).
Orders 3 and 4. Sarraceniaceæ and Nepenthaceæ. These two orders are perhaps most closely allied to the Droseraceæ and agree with these, among other things, in the manner of taking nourishment. Like the Droseraceæ they absorb nitrogenous food from dissolved animal matter by means of their leaves, which are specially constructed both to catch, to retain, and to digest any small animals which may be caught. The Sarraceniaceæ are North American marsh-plants (10 species) which have pitcher-like leaf-stalks, in the cavity of which a fluid (with properties approaching those of gastric juice) is secreted, and which bear at the apex a small, lid-like blade; these leaf-stalks are the catching and digestive organs.—Sarracenia, Darlingtonia.
