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 by cold, like the circulation of the blood in animals, because the activity of the vital energy bears a precise relation to the quantity of heat received. The gyration is instantly arrested by a shock of electricity.

The reproductive organs of the CharaceÆ are of two kinds, both growing in the axils of the branchlets, namely, dark-red globules, which are antheridia, and nucules or pistillidia, which contain germ cells. Sometimes they are found in different individuals, but in most of the Nitellas they are in the same individual, the globules being placed closely below the nucules, as in fig. 41, A, B. The envelope of the nearly spherical globules is formed of eight spherico-triangular valves. From the middle of the interior surface of these valves, a perpendicular orange-coloured column extends to the centre of the globule, where its summit is crowned with a mass of confervoid filaments, which are formed of a linear succession of minute cells; while from the base of the column, bands of orange-coloured spherules imbedded in gelatine radiate along the interior surface of the valve to its margin as shown at C, in the same figure. After successive changes in the matter within the confervoid filaments, (fig. 42, D-G), the microscope shows that ‘in every one of the cells there is formed a spiral thread of two or three coils, which, at first motionless, after a time begins to move and revolve within the cell; at last the cell wall gives way, and the spiral thread makes its way out, partially lengthens itself, and moves actively through the water in a tolerably determinate direction, by the lashing action of two long and very delicate filaments with which it is furnished’^[65] (fig. 42 H).

The nucule is an ovoid sac with five long cells spirally twisted round it, the sac being full of a viscous fluid containing globules of starch and oil. This nucule falls off when fertilized by the spirally-coiled ciliated bodies, and then germinates.

The CharaceÆ may also be artificially reproduced by cuttings; while under favourable circumstances they are reproduced by nodular bodies rich in starch grains, which arise from the creeping root, and also by clusters of cells called bulbils filled with starch grains, which arise from a modification of the nodes.

The Charas, properly so called, are monoecious or dioecious, more or less opaque and brittle, their many-jointed tubular stems bearing whorls of long slender awl-shaped branchlets. The fruit, accompanied by a cluster of short bracts or ramuli, is placed at intervals in the hollow side of the branchlets, one at each joint. In the bristly Chara the awl-shaped branchlets are simple, pointed at the extremity, and composed of about seven joints, with a whorl of from four to seven short bracts, and having fruit at each articulation. Many of the species of CharaceÆ are thickly incrusted with lime, and the whole order is exceedingly fetid.