In the group Endocarpei, the perithecia are immersed in the substance of the plant, which has, for the most part, a foliaceous horizontal crust, and a gelatinous nucleus. Some species grow on stones, perpetually or periodically submerged, or, if not under water, continually wet with its spray. The Lichina, a genus of the group Lichinei, lives on marine rocks, and is often dripping with salt-water, and often suddenly dried up. The Sphærophorei, or sphere-bearing lichens, have upright stems bearing globular fruit at the extremity of their numerous branches. At first, the fruit is only indicated by a swelling, but in time the outer bark bursts, and exposes the contents of the perithecium, which consist of asci and paraphyses seated on a central columella. The sporidia are beautiful objects under the microscope on account of their spherical form, which is rare among lichens, and their more or less deep blue tint—a colour by no means peculiar to the sporidia of this order of plants, for in other orders they are bright scarlet, olive, golden yellow, or brown. SECTION V. CHARACEÆ. [Illustration: Fig. 40. Nitella flexilis.] THE Characeæ are submerged annual water plants, growing in stagnant pools and ditches rather than in running streams. It is a small order containing but three genera, but the numerous species are dispersed all over the world, especially in temperate climates. The genera found in this country are Nitella and Chara. The Nitella flexilis (fig. 40) may be taken as a representative of the order. Its stem or axis is formed of very long cylindrical transparent tubes, joined by their flat ends, and surrounded at each junction by a whorl of long tubes which are forked or trifid at their extremities. In some species the branches are jointed, and have whorls precisely like those on the main axis. On the internal surface of the tubes, which are sometimes several inches in length, there are four longitudinal bands parallel to the axis of the tubes, which are occasionally twisted: two of these bands are broad and covered with oval green particles; while the other two are narrow, transparent, and colourless. Each tube is filled with a limpid semifluid liquid, in which pale green particles and jelly-like globules of a starchy nature float; and when these particles are watched with a microscope, they show that, in every tube of the plant, a continual current of that liquid, with its particles, ascends one of the green bands and descends by the other, even when the stem and branches are twisted; but they never flow in the colourless bands, though there is nothing to hinder them. According to the observations of microscopists there is probably a gyration of an azotized viscid fluid in all plants originating in, and maintained by, vital contractility of structure, but in none is it so evident as in the Characeæ. Its rate is increased by heat and diminished