own dots, each of which is part of a spermatozoid. When ripe, the
contents of the antheridium are forced out into the water (_G_),
leaving the empty outer wall behind, but still surrounded by a thin
membrane. After a few minutes this membrane is dissolved, and the
spermatozoids are set free. These (Fig. 27, _K_) are oval in form,
with two long cilia attached to the side where the brown speck, seen
while still within the antheridium, is conspicuous.

The act of fertilization may be easily observed by laying fresh
antheridia into a drop of water containing recently discharged egg
cells. To obtain these, all that is necessary is to allow freshly
gathered plants to remain in the air until they are somewhat dry,
when the ripe sexual cells will be discharged from the openings of
the conceptacles, exuding as little drops, those with antheridia
being orange-yellow; the masses of ooegonia, olive. Within a few
minutes after putting the ooegonia into water, the egg cells may be
seen to escape into the water, when some of the antheridia may be
added. The spermatozoids will be quickly discharged, and collect
immediately in great numbers about the egg cells, to which they
apply themselves closely, often setting them in rotation by the
movements of their cilia, and presenting a most extraordinary
spectacle (_J_). Owing to the small size of the spermatozoids, and
the opacity of the eggs, it is impossible to see whether more than
one spermatozoid penetrates it; but from what is known in other
cases it is not likely. The egg now secretes a wall about itself,
and within a short time begins to grow. It becomes pear-shaped, the
narrow portion becoming attached to the parent plant or to some
other object by means of rootlets, and the upper part grows into the
body of the young plant (Fig. 27, _M_).

[Illustration: FIG. 27.--_H_, the eight egg cells still surrounded by
the inner membrane of the ooegonium. _I_, the egg cells escaping into
the water. _J_, a single egg cell surrounded by spermatozoids. _K_,
mass of spermatozoids surrounded by the inner membrane of the
antheridium. _L_, spermatozoids. _M_, young plant. _r_, the roots.
_K_, x 300; _L_, x 600; the others, x 150.]

The simpler brown seaweeds, so far as known, multiply only by means of
zooespores, which may grow directly into new plants, or, as has been
observed in some species, two zooespores will first unite. A few, like
_Ect