In the preceding chapter we gave an account of certain plants which are parasitic on other plants and trees, deriving more or less of their nutriment from their vegetable hosts. One of these--the Tooth-wort (_Lathræa squamaria_), of the order _Orobanchaceæ_--is not only a parasite, deriving nourishment from the roots of trees, but is also a carnivorous species, feeding on minute animals which are captured and digested by its peculiar leaves; and therefore it may be conveniently considered here. The whole plant is of a fleshy character, and lives entirely underground, attached to the roots of the Hazel, Elm, or other tree, except during April and May, when it sends up thick flowering stems, from four to ten inches high, bearing a few broad, fleshy scales which gradually pass into bracts, and a one-sided spike or raceme of flowers. The stem and scales above ground are of a pale rose colour, and the flowers are either brown, flesh-colour or slightly bluish. The latter are numerous, closely placed, and either sessile or shortly stalked. The calyx is bell-shaped, nearly half an inch long, with four broad lobes; and the corolla, which is about half as long again as the calyx, is distinctly lipped. [Illustration: LONGITUDINAL SECTION (ENLARGED) THROUGH A LEAF OF THE TOOTH-WORT.] The whole plant is devoid of chlorophyll, and consequently has not the power of building up organic compounds after the manner of green plants; and, being parasitic on the roots of trees, it derives but little organic material from its host. To compensate for this the underground portion is so constructed that it can capture minute animals which exist in the soil, and has the power of digesting them and of absorbing the products of digestion. The underground stems are quite white, and are thickly covered with broad, cordate, fleshy leaves that closely overlap one another. There appears to be nothing very remarkable in these underground leaves until one has been removed from the stem and closely examined; and then we find that what appears to be the apex of the leaf is really its middle; and that what seems to be, at first sight, the under surface, is really an extension of the upper side; for the leaf is bent backwards in such a manner as to bring its apex close to the stem, immediately below its base. This peculiar folding of the leaf results in the formation of an irregular cavity, and the tip of the leaf, brought close to its base, is curled upward, close to the stem, in such a way as to form a little canal, with several small openings by which the cavity may be reached. It will not be easy to make out this strange folding of the leaf by an examination of the exterior only, but a longitudinal section, made with a sharp knife or razor, will show it clearly. [Illustration: COMMON BUTTERWORT.]