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._), × 150. _B_, surface view of the epidermis from the lower surface of a leaf. _f_, vein. _p_, breathing pore, × 150. _C_, longitudinal section of the fibro-vascular bundle of the leaf stalk, showing tracheids with ladder-shaped markings, × 150. _D_, longitudinal section through the tip of a root, × 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_), × 150. _F_, cross-section through a full-grown root, × 25. _r_, root hairs. _G_, the fibro-vascular bundle of the same, × 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 breathing pores (_stomata_, sing. _stoma_), not unlike those on the capsules of some of the bryophytes. Each breathing pore consists of two special crescent-shaped epidermal cells (guard cells), enclosing a central opening or pore communicating with an air space below. They arise from cells of the young epidermis that divide by a longitudinal wall, that separates in the middle, leaving the space between.