The leaves are constructed in the same manner as the stem; they are divided into a series of joints, but have only a limited power of growth; their terminal cell, too, is not enclosed by a cortex. Leaflets are borne at their nodes. The growth of the stem is unlimited, and proceeds by means of an apical cell (Fig. [62] s). The apical cell divides into a segment-cell and a new apical cell. The segment-cell then divides by a transverse wall into two cells, one lying above the other; the lower one, without any further division, becomes one of the long, cylindrical, internodal cells (Fig. [62] in), and the upper one (Fig. [62] n) divides by vertical walls to form the nodal cells. The cortical cells (Fig. [62] r) which surround the long internodal cells of Chara, are derived from the divisions of the nodal cells; the cells covering the upper portion of an internodal cell being derived from the node immediately above it, and those in the lower part of the internode from the node below it.
Fig. 62.—Chara fragilis: s apical cell; n, n nodal cells; in internodal cells; bl, bl leaves; r, r the cortical cells.
Fig. 63.—Oogonium of Chara: k “crown”; u receptive spot; s spermatozoids.
The organs of reproduction are very conspicuous by their colour and form. They are always situated on the leaves, the plants being very frequently monœcious. The antheridia (Fig. [61] B, a) are modified leaflets or the terminal cell of a leaf; they are spherical and become red when mature. Their wall consists of 8 “shields,” i.e. of plate-like cells, 4 of which cover the upper half, and are triangular; the 4 round the lower half, to which the stalk of the antheridia is attached, being quadrilateral, with sides of unequal length. The shields (Fig. [61] C) have dentated edges, with the teeth fitting into one another, and their faces ornamented with ridges. From the centre of the internal face of each shield (C) a cylindrical cell, the manubrium, projects nearly as far as the centre of the antheridium; at the inner end of each of the manubria a spherical cell, the capitulum, is situated. Each capitulum bears six secondary capitula, from each of which four long coiled filaments (C, D) project into the cavity of the antheridium. These filaments are divided by transverse walls into from 100–200 discoid cells, in each of which a biciliated, coiled spermatozoid is developed (D, E) from the nucleus. The spermatozoids escape from their mother-cell and are set free by the shields separating from one other.
The female organ of reproduction (Fig. [61] B, 63) is a small modified shoot, whose apical cell functions as an oogonium, its protoplasm forming the oosphere, which has a colourless receptive-spot at the summit (Fig. [63] u). The oogonium is situated on a nodal cell, from which 5 cells grow out in a circle and coil round the oogonium, covering it with a close investment. These cells divide once or twice at the top, so that 5 or 10 small cells are cut off, which project above the oogonium and form the so-called “crown” (Fig. [63] k). The crown either drops off at fertilisation, or its cells separate to form a central canal for the passage of the spermatozoids. The wall of the oosphere[9] above the receptive spot becomes mucilaginous, and allows the spermatozoid to fuse with the oosphere. The oospore, on germination (Fig. [64] sp), becomes a small filamentous plant of limited growth (Fig. [64] i, d, q, pl)—the proembryo—and from this, as a lateral outgrowth, the sexual generation is produced.
The order is divided into two sub-orders:—
A. Nitelleæ. The crown consists of 10 cells; cortex absent: Nitella, Tolypella.
B. Chareæ. The crown consists of 5 cells; cortex present: Tolypellopsis, Lamprothamnus, Lychnothamnus, Chara.