the manner of the Pillworts and
Quillworts. (See Fig. 521-526.)

[Illustration: Fig. 521. Small plant of Azolla Caroliniana. 522. Portion
magnified, showing the two kinds of sporocarp; the small ones contain
microspores. 523 represents one more magnified. 524. The larger
sporocarp more magnified. 525. Same more magnified and burst open,
showing stalked spore-cases. 526. Two of the latter highly magnified;
one of them bursting shows four contained macrospores; between the two,
three of these spores highly magnified.]

497. =Cellular Cryptogams= (483) are so called because composed, even in
their higher forms, of cellular tissue only, without proper wood-cells
or vessels. Many of the lower kinds are mere plates, or ribbons, or
simple rows of cells, or even single cells. But their highest orders
follow the plan of Ferns and phanerogamous plants in having stem and
leaves for their upward growth, and commonly roots, or at least
rootlets, to attach them to the soil, or to trunks, or to other bodies
on which they grow. Plants of this grade are chiefly Mosses. So as a
whole they take the name of

498. =Bryophyta, Bryophytes= in English form, Bryum being the Greek name
of a Moss. These plants are of two principal kinds: true Mosses
(_Musci_, which is their Latin name in the plural); and Hepatic Mosses,
or Liverworts (_Hepaticae_).

[Illustration: Fig. 527. Single plant of Physcomitrium pyriforme,
magnified. 528. Top of a leaf, cut across; it consists of a single layer
of cells.]

499. =Mosses or Musci.= The pale Peat-mosses (species of Sphagnum, the
principal component of sphagnous bogs) and the strong-growing Hair-cap
Moss (Polytrichum) are among the larger and commoner representatives of
this numerous family; while Fountain Moss (Fontinalis) in running water
sometimes attains the length of a yard or more. On the other hand, some
are barely individually distinguishable to the naked eye. Fig. 527
represents a common little Moss, enlarged to about twelve times its
natural size; and by its side is part of a leaf, much magnified, showing
that it is composed of cellular tissue (parenchyma-cells) only. The
leaves of Mosses are always simple, distinct, and sessile on the stem.
The fructification is an urn-shaped spore-case, in this as in most cases
raised on a slender stalk. The spore-case loosely bears on its summit a
thin and pointed cap, like a candle-extinguisher, called a _Calyptra_.
Detaching this, it is found that the spo