Flowerless plants with distinct leaves known as fronds, these circinate in the bud, except in one suborder, and bearing on the under surface or margin the clustered or separate sporangia or spore-cases.
Sporangia collected into various kinds of clusters called sori. Each sporangium pedicelled and encircled by an elastic jointed ring, by the breaking of which the sporangium is burst and the spores discharged. Sori sometimes covered by an indusium.
1. Polypo'dium. Fruit-dots on the back of the fronds near the ends of the veins. No indusium. Veins free. (See Fig. 231, Part I.)
2. Adiantum. Fruit-dots marginal, the edge of the frond being reflexed so as to form an indusium. Midrib of the pinnules close to the lower edge or altogether wanting. Stipe black and shining. All the pinnules distinct and generally minutely stalked. Veins free.
3. Pte'ris. Fruit-dots marginal. Indusium formed by the reflexed edge of the frond. Midrib of the pinnules in the centre and prominent. Veins free. Stipe light-coloured. (See Fig. 262.)
4. Pellae'a. Fruit-dots marginal, covered by a broad indusium. formed by the reflexed margin of the frond. Small ferns with once- or twice-pinnate fronds, the fertile ones very much like the sterile, but with narrower divisions. Stipe shining, purple or brown.
5. Asple'nium. Fruit-dots elongated (rarely curved), on veins on the back of the pinnules, oblique to the midrib, but only on the upper side of the vein(rarely attached to both sides). Indusium attached to the vein by one edge, the other edge free. Veins free.
6. Woodwar'dia. Fruit-dots elongated, on cross-veins parallel to the midrib, forming a chain-like row on each side of the latter. In-dusiurn as in the last. Veins reticulated.
7. Scolopen'drium. Fruit-dots elongated, occurring in pairs on contiguous veinlets, the free edges of the two indusia facing each other, so that the sori appear to be single, with an indusium split down the centre. Veins free. Frond simple, ribbon-shaped, about an inch broad, generally wavy-margined.
8. Camptoso'rus. Fruit elongated, those near the base of the midrib double, as in Scolopendrium; others single, as in Asplenium. Fronds simple, 1/2 to 3/4 of an inch wide at the heart-shaped base, and tapering into a long and narrow point; growing in tufts on limestone rocks, and commonly rooting at the tip of the frond, like a runner. Veins reticulated.
9. Phegop'teris. Fruit-dots roundish, on the back (not at the apex) of the veinlet, rather small. Indusium obsolete or none. Veins free. Fronds triangular in outline, in one species twice-pinnatifid, with a winged rhachis, and in the other in three petioled spreading divisions, the divisions once- or twice-pinnate.
10. Aspid'ium. Fruit-dots round. Indusium evident, flat, orbicular or kidney-shaped, fixed by the centre, opening all round the margin. Veins free. Generally rather large Ferns, from once- to thrice-pinnate. (See Fig. 264.)
11. Cystop'teris. Fruit-dots round. Indusium not depressed in the centre, but rather raised, attached to the frond not by the centre, but by the edge partly under the fruit-dot, and generally breaking away on the side towards the apex of the pinnule, and becoming reflexed as the sporangia ripen. Fronds slender and delicate, twice- or thrice-pinnate.
12. Struthiop'teris. Fertile frond much contracted and altogether unlike the sterile ones, the latter very large and growing in a cluster with the shorter fertile one in the centre. Rootstock very thick and scaly. Fertile fronds simply pinnate, the margins of the pinnae rolled backward so as to form a hollow tube containing the crowded sporangia. Very common in low grounds.
13. Onocle'a. Fertile and sterile fronds unlike. (See Figs. 266, 267, 268, 269, and accompanying description.)
14. Wood'sia. Small ferns with free veins. Sori round. Indusium very thin and delicate, attached by its base all round under the sorus, the top at length bursting into more or less narrow segments.
15. Dickso'nia. Fruit-dots round, very small, each on a recurved toothlet on the upper margin of the lobes of the pinnules, usually one to each lobe. Sporangia on an elevated globular receptacle, and enclosed in a cup-shaped indusium open at the top and partly adherent to the reflexed toothlet of the frond. Fronds minutely globular or hairy, 2-3 feet high, ovate-lanceolate in outline, pale green, very thin, without chaff.