1. AZÓLLA, Lam. ([Pl. 21.])
Small moss-like plants, the stems pinnately branched, covered with minute 2-lobed imbricated leaves, and emitting rootlets on the under side. Conceptacles in pairs beneath the stem; the smaller ones acorn-shaped, containing at the base a single macrospore with a few corpuscles of unknown character above it; the larger ones globose, and having a basal placenta which bears many pedicellate microsporangia which contain masses of microspores.
1. A. Caroliniàna, Willd. Plants somewhat deltoid in outline (4–12´´ broad), much branched; leaves with ovate lobes, the lower lobe reddish, the upper one green with a reddish border; macrospores with three attendant corpuscles, its surface minutely granulate; masses of microspores glochidiate.—Floating on quiet waters, from Lake Ontario westward and southward,—appearing like a reddish hepatic moss.
Salvínia nàtans, L., was said by Pursh to grow floating on the surface of small lakes in Western New York, and has more recently been said to occur in Missouri. It has oblong-oval floating leaves 4–6´´ long, closely pinnately-veined, which bear conceptacles and branching plumose fibres on their under surface.
Subclass II. CELLULAR ACROGENS, or BRYOPHYTES.
Plants composed of cellular tissue only. Antheridia or archegonia, or both, formed upon the stem or branches of the plant itself, which is developed from the germinating spore usually with the intervention of a filiform or conferva-like prothallus.—Divided into the Musci, or Mosses, and the Hepaticæ.
Division I. HEPÁTICÆ.[1] (Liverworts.)
[Footnote 1: Elaborated for this edition by Prof. L. M. Underwood, of Syracuse, N. Y.]
Plants usually procumbent, consisting of a simple thallus, a thalloid stem, or a leafy axis; leaves when present 2-ranked, with uniform leaf-cells and no midvein; thalloid forms with or without a midvein, smooth or scurfy or scaly beneath and usually with numerous rootlets. Sexual reproduction by antheridia and archegonia, which are immersed in the thallus, or sessile or pedicelled upon it, or borne on a peduncled receptacle. The fertilized archegonium develops into a capsule (sporogonium) closely invested by a calyptra, which ruptures above as the ripened capsule (containing numerous spores and usually elaters) pushes upward. It is also commonly surrounded by a usually double involucre, the inner (often called perianth) more or less tubular, the outer tubular or more often foliaceous, sometimes wholly wanting. Propagation is also effected by offshoots (innovations), runners (flagella), or by gemmæ, which appear at the margin of the leaves or on the surface of the thallus, often in special receptacles.