e macrosporangium at the base; the
others, microsporangia, x 3. _D_, a scale and microsporangium, x 5.
_E_, young microsporangium, x 150. The shaded cells are the spore
mother cells. _F_, a young macrospore, x 150. _G_, section of the
stem, x 50. _H_, a single fibro-vascular bundle, x 150. _I_, vertical
section of the female prothallium of _Selaginella_, x 50. _ar._
archegonium. _J_, section of an open archegonium, x 300. _o_, the egg
cell. _K_, microspore, with the contained male prothallium, x 300.
_x_, vegetative cell. _sp._ sperm cells. _L_, young plant, with the
attached macrospore, x 6. _r_, the first root. _l_, the first leaves.]

The leaves in most species are like those of the larger club mosses,
but more delicate. They are arranged in four rows on the upper side of
the stem, two being larger than the others. The smaller branches grow
out sideways so that the whole branch appears flattened, reminding one
of the habit of the higher liverworts. Special leafless branches (_B_,
_r_) often grow downward from the lower side of the main branches, and
on touching the ground develop roots which fork regularly.

The sporangia are much like those of the ground pines, and produced
singly at the bases of scale leaves arranged in a spike or cone (_A_,
_sp._), but two kinds of spores, large and small, are formed. In the
species figured the lower sporangium produces four large spores
(macrospores); the others, numerous small spores (microspores).

Even before the spores are ripe the development of the prothallium
begins, and this is significant, as it shows an undoubted
relationship between these plants and the lowest of the seed plants,
as we shall see when we study that group.

If ripe spores can be obtained by sowing them upon moist earth, the
young plants will appear in about a month. The microspore (Fig. 74,
_K_) produces a prothallium not unlike that of some of the water
ferns, there being a single vegetative cell (_x_), and the rest of
the prothallium forming a single antheridium. The spermatozoids are
excessively small, and resemble those of the bryophytes.

The macrospore divides into two cells, a large lower one, and a
smaller upper one. The latter gives rise to a flat disc of cells
producing a number of small archegonia of simple structure (Fig. 74,
_I_, _J_). The lower cell produces later a tissue that serves to
nourish the young embryo.

The development of the embryo recalls in some p