branches of the leaf. These secondary bundles
divide further, forming the veins of the leaflets.

The leaflets (_E_, _F_) are one-sided, the principal vein running
close to the lower edge, and the others branching from it, and forking
as they approach the upper margin, which is deeply lobed, the lobes
being again divided into teeth. The leaflets are very thin and
delicate, with extremely smooth surface, which sheds water perfectly.
If the plant is a large one, some of the leaves will probably bear
spores. The spore-bearing leaves are at once distinguished by having
the middle of each lobe of the leaflets folded over upon the lower
side (_F_). On lifting one of these flaps, numerous little rounded
bodies (spore cases) are seen, whitish when young, but becoming brown
as they ripen. If a leaf with ripe spore cases is placed upon a piece
of paper, as it dries the spores are discharged, covering the paper
with the spores, which look like fine brown powder.

[Illustration: FIG. 68.--_A_, vertical section of the leaf of the
maiden-hair fern, which has cut across a vein (_f.b._), x 150. _B_,
surface view of the epidermis from the lower surface of a leaf. _f_,
vein. _p_, breathing pore, x 150. _C_, longitudinal section of the
fibro-vascular bundle of the leaf stalk, showing tracheids with
ladder-shaped markings, x 150. _D_, longitudinal section through the
tip of a root, x 150. _a_, apical cell. _Pl._ young fibro-vascular
bundle. _Pb._ young ground tissue. _E_, cross-section of the root,
through the region of the apical cell (_a_), x 150. _F_, cross-section
through a full-grown root, x 25. _r_, root hairs. _G_, the
fibro-vascular bundle of the same, x 150.]

A microscopical examination of the leaf stalk shows the tissues to
be almost exactly like those of the stem, except the inner ground
tissue, whose cells are thin-walled and colorless (soft tissue or
"parenchyma") instead of stony tissue. The structure of the blade of
the leaf, however, shows a number of peculiarities. Stripping off a
little of the epidermis with a needle, or shaving off a thin slice
with a razor, it may be examined in water, removing the air if
necessary with alcohol. It is composed of a single layer of cells,
of very irregular outline, except where it overlies a vein (Fig. 68,
_B_, _f_). Here the cells are long and narrow, with heavy walls. The
epidermal cells contain numerous chloroplasts, and on the under
surface of the leaf br