HTDROPTERIDES. (MARSILEACE^E.) 605 



er; the two sorts of fructification in the same axils. (Lycopodhim rupestre, L.) 

 Dry and exposed rocks; common. Grayish-green in aspect, resembling a 

 rigid Moss. 



* * Leaves of 2 sorts, the shorter above and below, resembling stipules, the larger 



lateral, 2-ranked. 



3. S. a pus, Spring. Stems tufted and prostrate, creeping, much branched, 

 flaccid ; leaves pellucid-membranaceous, the larger spreading horizontally, ovate, 

 oblique, mostly obtuse ; the others smaller, appressed, taper-pointed ; those of 

 the short spikes nearly similar; oophoridia copious at the lower part of the 

 spike. (Lycopodium apodum, L.) Low, shady places, S. New England, 

 near the coast, to Virginia, and southward. A delicate little plant, resembling 

 a Moss or Jungermannia. 



ORDER 138. HYDROPTERIDES. (MARSILEACE.B, R. Br.) 



Aquatic cryptogamous plants, of diverse habit, urith the fructification borne 

 at the bases of the leaves, or on submerged branches, consisting of two sorts 

 of organs, contained in indehiscent or irregularly bursting involucres (sporo- 

 carps) : here represented by only two genera ; one of them, Isoetes, 

 nearly related to Club-Mosses in structure ; the other, Azolla, much like a 

 floating Liverwort. 



1. ISOETES, L. QUILLWOET. (Tab. 14.) 



Stem a mere succulent base or crown, rooting from underneath, and covered 

 above with the dilated imbricated bases of the elongated terete awl-shaped or 

 stalk-like cellular leaves. Sporocarps ovoid and plano-convex, pretty large, 

 sessile in the axils of the leaves and united with or enveloped by their excavated 

 dilated base, very thin, traversed internally by transverse threads, forming a 

 kind of partitions ; those of the central leaves filled with very minute powdery- 

 grains (analogous to the spores of Lycopodium) ; the exterior filled with larger 

 spherical-quadrangular spores (oophoridia), at first cohering in fours, their crus- 

 taceous integument marked by 3 radiant lines. (Name composed of uros, equal, 

 nd eras, year ; perhaps intended to indicate that these aquatic plants are un- 

 changed by the season, i. e. alike the year through.) 



1. I. lacftstris, L. Crown or rootstock broad and depressed ; leaves whol- 

 ly submersed, dark green, rigid and fragile, awl-shaped (2' -6' long), the dilated 

 base as broad as long ; spores (oophoridia) roughish-granulated, scarcely reticu- 

 lated. Bottom of ponds and slow streams ; not rare northward. New Eng- 

 land specimens agree well with the European plant, and also seem too nearly 1 

 like the next. The following species are admitted in deference to authority : 

 but probably all are forms of one. (Eu.) 



2. I. rip aria, Engelm. Crown small; leaves slender, soft, yellowish- 

 green (4' -6' long), the base broader than long; spores minutely farinaceous 

 and reticulated. Gravelly banks of the Delaware below Philadelphia, between 



51* 



