A microscopical examination of the stem and leaves shows their
structure to be very simple. The former is cylindrical, and composed
of nearly uniform elongated cells, with straight cross-walls. The
leaves consist of a single layer of small, roundish cells, which,
like those of the stem, contain numerous rounded chloroplasts, to
which is due their dark green color.

The tissues are developed from a single apical cell, but it is
difficult to obtain good sections through it.

The antheridia are borne singly at the bases of the leaves on the
special branches already described (Fig. 53, _A_, _an._). By
carefully dissecting with needles such a branch in a drop of water,
some of the antheridia will usually be detached uninjured, and may
be readily studied, the full-grown ones being just large enough to
be seen with the naked eye. They are globular bodies, attached by a
stalk composed of two rows of cells. The globular portion consists
of a wall of chlorophyll-bearing cells, composed of two layers
below, but single above (Fig. 53, _C_). Within is a mass of
excessively small cells, each of which contains a spermatozoid. In
the young antheridium (_A_, _an._) the wall is single throughout,
and the central cells few in number. To study them in their natural
position, thin longitudinal sections of the antheridial branch
should be made.

[Illustration: FIG. 53.--_A_, end of a branch from a male plant of
_Madotheca_. The small side branchlets bear the antheridia, x 2. _B_,
two young antheridia (_an._), the upper one seen in optical section,
the lower one from without, x 150. _C_, a ripe antheridium, optical
section, x 50. _D_, sperm cells with young spermatozoids. _E_, ripe
spermatozoids, x 600.]

When ripe, if brought into water, the antheridium bursts at the top
into a number of irregular lobes that curl back and allow the mass
of sperm cells to escape. The spermatozoids, which are derived
principally from the nucleus of the sperm cells (53, _D_) are so
small as to make a satisfactory examination possible only with very
powerful lenses. The ripe spermatozoid is coiled in a flat spiral
(53, _E_), and has two excessively delicate cilia, visible only
under the most favorable circumstances.

The female organ in the bryophytes is called an "archegonium," and
differs considerably from anything we have yet studied, but recalls
somewhat the structure of the ooegonium of