nd give rise to new plants. These spores, it will be noticed,
differ in one important particular from corresponding spores in most
algae, in being unprovided with cilia, and incapable of spontaneous
movement.

Occasionally in the same plant that bears tetraspores, but more
commonly in special ones, there are produced the sexual organs, and
subsequently the sporocarps, or fruits, developed from them. The
plants that bear them are usually stouter that the non-sexual ones,
and the masses of ripe carpospores are large enough to be readily
seen with the naked eye.

If a plant bearing ripe spores is selected, the young stages of the
female organ (procarp) may generally be found by examining the
younger parts of the plant. The procarp arises from a single cell of
the filament. This cell undergoes division by a series of
longitudinal walls into a central cell and about four peripheral
ones (Fig. 29, _D_ i). One of the latter divides next into an upper
and a lower cell, the former growing out into a long, colorless
appendage known as a trichogyne (Fig. 29, _D_, _tr._).

The antheridia (Fig. 29, _E_) are hemispherical masses of closely
set colorless cells, each of which develops a single spermatozoid
which, like the tetraspores, is destitute of cilia, and is dependent
upon the movement of the water to convey it to the neighborhood of
the procarp. Occasionally one of these spermatozoids may be found
attached to the trichogyne, and in this way fertilization is
effected. Curiously enough, neither the cell which is immediately
fertilized, nor the one beneath it, undergo any further change; but
two of the other peripheral cells on opposite sides of the filament
grow rapidly and develop into large, irregular masses of spores
(Fig. 29, _D_ III, IV).

While the plant here described may be taken as a type of the group,
it must be borne in mind that many of them differ widely, not only in
the structure of the plant body, but in the complexity of the sexual
organs and spores as well. The tetraspores are often imbedded in the
tissues of the plant, or may be in special receptacles, nor are they
always arranged in the same way as here described, and the same is
true of the carpospores. These latter are in some of the higher forms,
_e.g._ _Polysiphonia_ (Fig. 29, _F_), contained in urn-shaped
receptacles, or they may be buried within the tissues of the plant.

[Illustration: FIG. 30.