r
and more compact toward the outside of the section, until there are
no spaces of any size between those of the outside or rind. The
cells contain small chloroplasts like those of the higher plants,
but owing to the presence of the brown pigment found in all of the
class, in addition to the chlorophyll, they appear golden brown
instead of green.

No non-sexual reproductive bodies are known in the rock weeds,
beyond small branches that occur in clusters on the margins of the
main branches, and probably become detached, forming new plants. In
some of the lower forms, however, _e.g._ _Ectocarpus_ and
_Laminaria_ (Fig. 28, _A_, _C_), zooespores are formed.

The sexual organs of the rock weed, as we have already seen, are
borne in special cavities (conceptacles) in the enlarged ends of
some of the branches. In the species here figured, _F. vesiculosus_,
the antheridia and ooegonia are borne on separate plants; but in
others, _e.g._ _F. platycarpus_, they are both in the same
conceptacle.

The walls of the conceptacle (Fig. 26, _B_) are composed of closely
interwoven filaments, from which grow inward numerous hairs, filling
up the space within, and often extending out through the opening at
the top.

The reproductive bodies arise from the base of these hairs. The
ooegonia (Fig. 26, _C_, _E_) arise as nearly colorless cells, that
early become divided into two cells, a short basal cell or stalk and
a larger terminal one, the ooegonium proper. The latter enlarges
rapidly, and its contents divide into eight parts. The division is
at first indicated by a division of the central portion, which
includes the nucleus, and is colored brown, into two, four, and
finally eight parts, after which walls are formed between these. The
brown color spreads until the whole ooegonium is of a nearly uniform
olive-brown tint.

When ripe, the upper part of the ooegonium dissolves, allowing the
eight cells, still enclosed in a delicate membrane, to escape
(Fig. 27, _H_). Finally, the walls separating the inner cells of the
ooegonium become also absorbed, as well as the surrounding membrane,
and the eight egg cells escape into the water (Fig. 27, _I_) as
naked balls of protoplasm, in which a central nucleus may be dimly
seen.

The antheridia (Fig. 26, _F_, _G_) are small oblong cells, at first
colorless, but when ripe containing numerous glistening, reddish
br