ermal cells, then larger chlorophyll-bearing cells, and
in the centre a group of very delicate, small, colorless cells,
which in longitudinal section are seen to be elongated, and similar
to those forming the midrib of the leaf. These cells probably serve
for conducting fluids, much as the similar but more perfectly
developed bundles of cells (fibro-vascular bundles) found in the
stems and leaves of the higher plants.

The root hairs, fastening the plant to the ground, are rows of
cells with brown walls and oblique partitions. They often merge
insensibly into the green filaments (protonema) already noticed.
These latter have usually colorless walls, and more numerous
chloroplasts, looking very much like a delicate specimen of
_Cladophora_ or some similar alga. If a sufficient number of these
filaments is examined, some of them will probably show young moss
plants growing from them (Fig. 63, _A_, _k_), and with a little
patience the leafy plant can be traced back to a little bud
originating as a branch of the filament. Its diameter is at first
scarcely greater than that of the filament, but a series of walls,
close together, are formed, so placed as to cut off a pyramidal cell
at the top, forming the apical cell of the young moss plant. This
apical cell has the form of a three-sided pyramid with the base
upward. From it are developed three series of cells, cut off in
succession from the three sides, and from these cells are derived
all the tissues of the plant which soon becomes of sufficient size
to be easily recognizable.

The protonemal filaments may be made to grow from almost any part of
the plant by keeping it moist, but grow most abundantly from the
base of the stem.

The sexual organs are much like those of the liverworts and are
borne at the apex of the stems.

The antheridia (Figs. 59, 60) are club-shaped bodies with a short
stalk. The upper part consists of a single layer of large
chlorophyll-bearing cells, enclosing a mass of very small, nearly
cubical, colorless, sperm cells each of which contains an
excessively small spermatozoid.

The young antheridium has an apical cell giving rise to two series
of segments (Fig. 60, _A_), which in the earlier stages are very
plainly marked.

When ripe the chlorophyll in the outer cells changes color, becoming
red, and if a few such antheridia from a plant that has been kept
rather dr