The Charas, properly so called, are monœcious or diœcious, 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. [Illustration: Fig. 42. Antheridia of Chara fragilis:—D, E, F, successive stages of formation of spermatozoids in the linear cells of the antheridial filaments; G, escape of mature spermatozoids, which are shown detached at H.] SECTION VI. HEPATICÆ, OR LIVERWORTS. THE Hepaticæ are the small herbaceous plants, which constitute the three distinct natural orders called respectively Ricciaceæ, Marchantiaceæ, and Jungermanniaceæ. They are distinguished primarily by the first having the sporangia valveless, without elaters; by the second having dependent valvate or irregularly bursting sporangia; and by the third having the sporangia valvate and erect. Both the latter, moreover, have the spores mixed with elaters. The Ricciaceæ, popularly called Crystalworts, which form the lowest grade of Hepaticæ, are inconspicuous plants, growing in mud, or floating on water. They have spreading, horizontal fronds, of a delicate cellular structure and of indefinite form. Their fructification consists of valveless spherical sporangia, or spore sacs, imbedded in the frond; cells are formed within these sporangia, each of which cells is divided into four parts, which become spores, and, when ripe, the surface of the sporangia is fractured to give them egress. In some species there are many air passages in the cavities where the sporangia are produced. The under-surface of the frond is often beset with scales. The genus Riella differs from all the other genera in having an upright branchless stem with a distinct wing or limb forming a continuous spiral round it. In the male plant, the edge of the frond bears the antheridia containing spermatozoids; in the female plant the sporangia spring from the stem; they have a separate envelope, and the spores are echinate. [Illustration: Fig. 43. Marchantia polymorpha:—_a_, gemmiparous conceptacles; _b_, lobed receptacles bearing pistillidia.]