10. E. variegàtum, Schleicher. Stems ascending (6–18´ long), usually simple from a branched base, 5–10-grooved; sheaths green variegated with black above, the 5–10 teeth tipped with a deciduous bristle.—Shores or river-banks, N. H. (Bellows Falls, Carey) and Niagara to Minn., and northward; rare. (Eu.)
11. E. scirpoìdes, Michx. Stems very numerous in a tuft, filiform (3–6´ high), flexuous and curving, mostly 6-grooved, with acute ridges; sheaths 3-toothed, the bristle-pointed teeth more persistent; central air-cavity wanting.—Wooded hillsides, N. Eng. to Penn., Minn., and northward. (Eu.)
Leafy plants, with the leaves (fronds) usually raised on a stalk or petiole (stipe), rising from a (sometimes greatly elongated) rootstock, separately rolled up (circinate) in the bud, and bearing on the under surface or along the margin small reticulated sporangia, which at length split open and discharge the numerous minute spores. Prothallus green, above ground, normally monœcious.
Suborder I. Polypodiàceæ. Sporangia collected in dots, lines, or variously shaped clusters (sori or fruit-dots) on the back or margins of the frond or its divisions, cellular-reticulated, stalked, the stalk running into a vertical incomplete many-jointed ring, which by straightening at maturity ruptures the sporangium transversely on the inner side, discharging the spores. Fruit dots often covered (at least when young) by a membrane called the indusium (or less properly the involucre), growing either from the back or the margin of the frond. ([Plates 16–19.])
Tribe I. POLYPODIEÆ. Fructification on the back of the frond, in round or roundish fruit-dots (sori) placed on the veins or at the ends of the veins, without indusium of any kind. Stipes articulated to the rootstock, leaving a distinct scar when separated. Veins free (not reticulated) in our species.
1. Polypodium. Sori round, in one or more rows, on each side of the midrib or of the segments of the frond.
Tribe II. GRAMMITIDEÆ. Sori more or less elongated, without indusium, placed on the back of the frond, usually along the veins or near their extremities. Veins free in our species.
2. Notholæna. Sori short, of few rather large sporangia, placed near the tips of the veins; under surface of the frond usually either chaffy, woolly, or powdery.
Tribe III. PTERIDEÆ. Fructification marginal or intramarginal, provided with a general indusium formed of the (either altered or unchanged) margin of the frond. Stipes not articulated to the rootstock. Veins free in all our species.