602 HYDROPTERIDES. (WATER-FERN FAMILY.) 
Orper 164. HYDROPTERIDES. (Warer-Fern FAMILY.) 
Aquatic herbs, with the sporangia of two enk borne at the base of 
the leaves and bursting irregularly. 
1. ISOETES, L. 
Plants composed of fibrous roots and filiform cellular leaves, without any ap- 
parent stem. Sporangia sunk in an excavation of the dilated base of the leaves, 
plano-convex, membranaceous, filled with transverse threads and minute pow- 
dery spores; those of the central leaves filled with larger spores.. 
1. I. flaccida, Shuttlw. Immersed; leaves very long (139 - 2), slender, 
flaccid, yellowish-green ; spores very small, minutely pulverulent, not reticulated. 
— Inlakes and clear streams, Middle and West Florida. 
2. AZOLLA, Lam. 
Minute floating plants, with pendent roots, pinnately branching stems, and 
thick imbrieated cellular leaves. Sporangia of two kinds, ovoid, sessile on the 
under side of the branches, and covered with a thin membrane; the smaller kind 
opening transversely, containing several angular grains, attached to a central col- 
umn, the larger bursting irregularly and containing numerous globular stalked 
spores. 
1. A. Caroliniana, Willd. — On still water, chiefly near the coast, Flor- 
ida, and northward. — Plant reddish, circular in outline, j'/-1' in diameter. 
Leaves ovate, obtuse, rounded and roughened on the back. 
