Very often peculiar hairs or scales (_paleæ_, _ramenta_), dry, brown, flat and broad, are found on stem and leaf. The SPORANGIA are small, round capsules, which, in a very large number of Ferns, are formed on the back, but more rarely on the edge of the ordinary foliage-leaves. It is very seldom that there is any difference in form between the barren foliage-leaves and the fertile leaves, as is found for example in _Blechnum spicant_ or _Struthiopteris_; or that the fertile part of the leaf is differently constructed from the barren portion of the same leaf, as in the Royal-Fern (_Osmunda_). In such instances the mesophyll of the fertile parts is poorly developed. The sporangia in the _Polypodiaceæ_ are lens-shaped, with long stalk (Fig. 211 _D_): their wall consists of one cell-layer on which a single row of cells, passing vertically over the top (that is along the edge of the sporangium), is developed into the “ring” (annulus). The cells of the annulus are very much thickened on the inner and side walls, and are yellowish-brown. The thickened cells, however, do not entirely encircle the sporangium, and on one side, near the stalk, they pass over into large, flat, thin-walled cells. These form a weak point in the wall, and it is here that the sporangium is opened diagonally by the elongation of the annulus. The sporangium of the Polypodiaceæ opens as it dries. The cells of the annulus are very hygroscopic, and in straightening, the annulus bends back with a jerk, thus ejecting the spores to considerable distances. The cells of the annulus absorb water with great readiness. [The sporangium arises as a single epidermal cell, from which a basal stalk-cell is cut off. Three oblique cell-walls, intersecting near the base, are next formed in the upper cell, and a fourth between these and parallel to the free surface; an inner tetrahedral cell enclosed by four others is thus formed, the outer cells become the wall of the sporangium, while the inner cell, by a series of walls, parallel to its sides, cuts off a layer of cells which eventually form the tapetum, the remaining central cell constituting the archesporium.] The SPORES are either oblong and bilateral, or they are tetrahedric with curved sides, depending upon the way in which the tetrad division has taken place. The sporangia are almost always situated on the nerves and gathered into groups, _sori_, which differ in form in the various genera. The sori, in many genera, may be covered by a scale-like structure, the _indusium_ (Figs. 211 _B_, 212). In the majority of cases, each sorus is situated on a small papilla (_placenta_, or _receptacle_), which is supplied by a small vascular bundle. Between the sporangia, hairs (_paraphyses_) are often situated, which spring either from the placenta or from the stalks of the sporangia.