0. Branch of a Chara, about natural size. 551. A
fruiting portion, magnified, showing the structure; a sporocarp, and an
antheridium. 552. Outlines of a portion of the stem in section, showing
the central cell and the outer or cortical cells.]

506. =Characeae.= These are aquatic herbs, of considerable size,
abounding in ponds. The simpler kinds (Nitella) have the stem formed of
a single row of tubular cells, and at the nodes, or junction of the
cells, a whorl of similar branches. Chara (Fig. 550-552) is the same,
except that the cells which make up the stem and the principal branches
are strengthened by a coating of many smaller tubular cells, applied to
the surface of the main or central cell. The fructification consists of
a globular sporocarp of considerable size, which is spirally enwrapped
by tubular cells twisted around it: by the side of this is a smaller and
globular antheridium. The latter breaks up into eight shield-shaped
pieces, with an internal stalk, and bearing long and ribbon shaped
filaments, which consist of a row of delicate cells, each of which
discharges a free-moving microscopic thread (the analogue of the pollen
or pollen-tube), nearly in the manner of Ferns and Mosses. One of these
threads reaches and fertilizes a cell at the apex of the nucleus or
solid body of the sporocarp. This subsequently germinates and forms a
new individual.

507. =Algae or Seaweeds.= The proper Seaweeds may be studied by the aid
of Professor Farlow's "Marine Algae of New England;" the fresh-water
species, by Prof. H. C. Woods's "Fresh-water Algae of North America," a
larger and less accessible volume. A few common forms are here very
briefly mentioned and illustrated, to give an idea of the family. But
they are of almost endless diversity.

[Illustration: Fig. 553. Agarum Turneri, Sea Colander (so called from
the perforations with which the frond, as it grows, becomes riddled);
very much reduced in size.]

[Illustration: Fig. 554. Upper end of a Rockweed, Fucus vesiculosus,
reduced half or more, _b_, the fructification.]

508. The common Rockweed (Fucus vesiculosus, Fig. 554, abounding between
high and low water mark on the coast), the rarer Sea Colander (Agarum
Turneri, Fig. 553), and Laminaria, of which the larger forms are called
Devil's Aprons, are good representatives of the olive green or brownish
Seaweeds. They are attached either by a disk-like base or by root-like
holdfasts to the rocks or stones on which