mall male plant of _Funaria_. _a_, _a'_, antheridia. _p_, paraphysis.
_L_, section of a leaf, x 150.]

This moss is dioecious. The male plants are smaller than the female,
and may be recognized by the bright red antheridia which are formed at
the end of the stem in considerable numbers, and surrounded by a
circle of leaves so that the whole looks something like a flower.
(This is still more evident in some other mosses. See Figure 65, _E_,
_F_.)

The leaves when magnified are seen to be composed of a single layer
of cells, except the midrib, which is made up of several thicknesses
of elongated cells. Where the leaf is one cell thick, the cells are
oblong in form, becoming narrower as they approach the midrib and
the margin. They contain numerous chloroplasts imbedded in the layer
of protoplasm that lines the wall. The nucleus (Fig. 63, _C_, _n_)
may usually be seen without difficulty, especially if the leaf is
treated with iodine. This plant is one of the best for studying the
division of the chloroplasts, which may usually be found in all
stages of division (Fig. 63, _D_). In the chloroplasts, especially
if the plant has been exposed to light for several hours, will be
found numerous small granules, that assume a bluish tint on the
application of iodine, showing them to be starch grains. If the
plant is kept in the dark for a day or two, these will be absent,
having been used up; but if exposed to the light again, new ones
will be formed, showing that they are formed only under the action
of light.

[Illustration: FIG. 60.--_A_, _B_, young antheridia of _Funaria_,
optical section, x 150. _C_, two sperm cells of _Atrichum_. _D_,
spermatozoids of _Sphagnum_, x 600.]

Starch is composed of carbon, hydrogen, and oxygen, and so far as is
known is only produced by chlorophyll-bearing cells, under the
influence of light. The carbon used in the manufacture of starch is
taken from the atmosphere in the form of carbonic acid, so that
green plants serve to purify the atmosphere by the removal of this
substance, which is deleterious to animal life, while at the same
time the carbon, an essential part of all living matter, is combined
in such form as to make it available for the food of other
organisms.

The marginal cells of the leaf are narrow, and some of them
prolonged into teeth.

A cross-section of the stem (63, _E_) shows on the outside a single
row of epid