rably.

The fresh spores begin to germinate within about twenty-four hours,
and the early stages, which closely resemble those of the ferns, may
be easily followed by sowing the spores in water. With care it is
possible to get the mature prothallia, which should be treated as
described for the fern prothallia. Under favorable conditions, the
first antheridia are ripe in about five weeks; the archegonia, which
are borne on separate plants, a few weeks later. The antheridia
(Fig. 72, _J_, _an._) are larger than those of the ferns, and the
spermatozoids (_K_) are thicker and with fewer coils, but otherwise
much like fern spermatozoids.

The archegonia have a shorter neck than those of the ferns, and the
neck is straight.

Both male and female prothallia are much branched and very irregular
in shape.

There are a number of common species of _Equisetum_. Some of them,
like the common scouring rush (_E. hiemale_), are unbranched, and the
spores borne at the top of ordinary green branches; others have all
the stems branching like the sterile stems of the field horse-tail,
but produce a spore-bearing cone at the top of some of them.

CLASS III.--THE CLUB MOSSES (_Lycopodinae_).

The last class of the pteridophytes includes the ground pines, club
mosses, etc., and among cultivated plants numerous species of the
smaller club mosses (_Selaginella_).

Two orders are generally recognized, although there is some doubt as
to the relationship of the members of the second order. The first
order, the larger club mosses (_Lycopodiaceae_) is represented in the
northern states by a single genus (_Lycopodium_), of which the common
ground pine (_L. dendroideum_) (Fig. 73) is a familiar species. The
plant grows in the evergreen forests of the northern United States as
well as in the mountains further south, and in the larger northern
cities is often sold in large quantities at the holidays for
decorating. It sends up from a creeping, woody, subterranean stem,
numerous smaller stems which branch extensively, and are thickly set
with small moss-like leaves, the whole looking much like a little
tree. At the ends of some of the branches are small cones (_A_, _x_,
_B_) composed of closely overlapping, scale-like leaves, much as in a
fir cone. Near the base, on the inner surface of each of these scales,
is a kidney-shaped capsule (_C_, _sp._) opening by a cleft along the
upper edge and filled with a mass of fin