st root hair (Fig. 66, _B_, _C_,
_r_). The body of the spore containing most of the chlorophyll
elongates more slowly, and divides by a series of transverse walls
so as to form a short row of cells, resembling in structure some of
the simpler algae (_C_).

In order to follow the development further, spores must be sown upon
earth, as they do not develop normally in water beyond this stage.

In studying plants grown on earth, they should be carefully removed
and washed in a drop of water so as to remove, as far as possible,
any adherent particles, and then may be mounted in water for
microscopic examination.

In most cases, after three or four cross-walls are formed, two walls
arise in the end cell so inclined as to enclose a wedge-shaped cell
(_a_) from which are cut off two series of segments by walls
directed alternately right and left (Fig. 66, _D_, _E_, _a_), the
apical cell growing to its original dimensions after each pair of
segments is cut off. The segments divide by vertical walls in
various directions so that the young plant rapidly assumes the form
of a flat plate of cells attached to the ground by root hairs
developed from the lower surfaces of the cells, and sometimes from
the marginal ones. As the division walls are all vertical, the plant
is nowhere more than one cell thick. The marginal cells of the young
segments divide more rapidly than the inner ones, and soon project
beyond the apical cell which thus comes to lie at the bottom of a
cleft in the front of the plant which in consequence becomes
heart-shaped (_E_, _F_). Sooner or later the apical cell ceases to
form regular segments and becomes indistinguishable from the other
cells.

In the ostrich fern and lady fern the plants are dioecious. The male
plants (Fig. 66, _J_) are very small, often barely visible to the
naked eye, and when growing thickly form dense, moss-like patches.
They are variable in form, some irregularly shaped, others simple
rows of cells, and some have the heart shape of the larger plants.

The female plants (Fig. 66, _F_) are always comparatively large and
regularly heart-shaped, occasionally reaching a diameter of nearly or
quite one centimetre, so that they are easily recognizable without
microscopical examination.

All the cells of the plant except the root hairs contain large and
distinct chloroplasts much like those in the leaves of the moss, and
l