A section of the rhizome exhibits the fibro-vascular tissue arranged differently from that in the stems of either Exogens or Endogens. It forms curiously curved longitudinal plates, a very abundant component of which is the scalar´iform (_scala_, a ladder) duct (Pl. II. fig. 34). The walls of the scalariform ducts are angular, and the secondary deposit is arranged in the form of transverse bars, somewhat resembling the steps of a ladder; which structure is best seen in a transverse or slightly oblique section. The fronds are usually cleft nearly down to the main vein or midrib (fig. 9), or pinnatifíd (_pinna_, a feather, _findo_, to cleave); sometimes the segments are similarly cleft, so that the fronds are bipinnatifid. The manner in which the veins usually branch is also peculiar, each branch separating from the point of division at an acute angle with the original direction of the vein (fig. 20), so as to be forked. It is also worthy of notice, that the young frond is rolled up into a flat spiral, or is cir´cinate (_circino_, to go round), before it opens. We will now examine one or two species more minutely. POLYPODIACEÆ. _Polypódium vulga´re_ (Pl. II. fig. 9, one-third of the natural size), a member of this family, is very common on old trunks of trees, on banks, &c. The frond is deeply pinnatifid, the segments being oblong, blunt (obtuse), scalloped (crenate) at the edges (PI. II. fig. 10), and becoming gradually shorter towards the apex of the frond. On the back of the fronds are the little orange-coloured groups of capsules (Pl. II. figs. 9 & 10); these are called _sor´i_ (σορὀς, a heap). The capsules or _thécæ_ (θἡκη, a case), a magnified group of which is represented in fig. 11, consist each of an aggregation of cells, fixed to a stalk (fig. 12); and along the back of the capsule is a close row of thicker cells, forming an elastic ring, the _an´nulus_. When the seed-like bodies or spores (σπορἁ, a seed) are ripe, the annulus becomes straightened from its elastic power, and tears the capsule open, so that the spores are set free and scattered. _Aspid´ium filix mas_ (Pl. II. fig. 16, reduced to one third or fourth of the natural size), is the most common British fern. In this the fronds are pinnate, _i. e._ the segments (pinnæ) corresponding to those of _Polypodium_ are cleft entirely to the main stalk, the pinnæ (fig. 17) being pinnatifid; and the segments of the pinnæ or the pinnules (fig. 18) are oblong, obtuse, and saw-edged (serrate). In all botanical works the fronds are incorrectly said to be bipinnate. The sori are brown, kidney-shaped (fig. 18), and differ from those of _Polypodium_ in being covered by a thin membrane (_indúsium_), which is fixed to the frond at the notch.