fine hairs like those on the lower surface of the
liverworts, which fasten it firmly to the ground. By and by, if our
culture has been successful, we may find attached to some of the
larger of these, little fern plants growing from the under side of the
prothallia, and attached to the ground by a delicate root. As the
little plant becomes larger the prothallium dies, leaving it attached
to the ground as an independent plant, which after a time bears the
spores.

[Illustration: FIG. 66.--_A_, spore of the ostrich fern (_Onoclea_),
with the outer coat removed. _B_, germinating spore, x 150. _C_, young
prothallium, x 50. _r_, root hair. _sp._ spore membrane. _D_, _E_,
older prothallia. _a_, apical cell, x 150. _F_, a female prothallium,
seen from below, x 12. _ar._ archegonia. _G_, _H_, young archegonia,
in optical section, x 150. _o_, central cell. _b_, ventral canal cell.
_c_, upper canal cell. _I_, a ripe archegonium in the act of opening,
x 150. _o_, egg cell. _J_, a male prothallium, x 50. _an._ antheridia.
_K_, _L_, young antheridia, in optical section, x 300. _M_, ripe
antheridium, x 300. _sp._ sperm cells. _N_, _O_, antheridia that have
partially discharged their contents, x 300. _P_, spermatozoids, killed
with iodine, x 500. _v_, vesicle attached to the hinder end.]

In choosing spores for germination it is best to select those of large
size and containing abundant chlorophyll, as they germinate more
readily. Especially favorable for this purpose are the spores of the
ostrich fern (_Onoclea struthiopteris_) (Fig. 70, _I_, _J_), or the
sensitive fern (_O. sensibilis_). Another common and readily grown
species is the lady fern (_Asplenium filixfoemina_) (Fig. 70, _H_). The
spores of most ferns retain their vitality for many months, and hence
can be kept dry until wanted.

The first stages of germination may be readily seen by sowing the
spores in water, where, under favorable circumstances, they will
begin to grow within three or four days. The outer, dry, brown coat
of the spore is first ruptured, and often completely thrown off by
the swelling of the spore contents. Below this is a second colorless
membrane which is also ruptured, but remains attached to the spore.
Through the orifice in the second coat, the inner delicate membrane
protrudes in the form of a nearly colorless papilla which rapidly
elongates and becomes separated from the body of the spore by a
partition, constituting the fir