On the North American Species of Isottes and Marsilea. 58 
plants, and may in the same manner be obtained for botanical 
gardens. The specimens of J. sefacea cultivated by me, had 
been preserved in an herbarium near two years, when I had the 
pleasure to see them vegetate, soon after throwing them in water. 
I give the characters of both European Species, with the 
American, in order that they may be compared together. 
1. Isoétes lacustris, Linn. Submersed ; rhizoma placenta-shaped, 
depressed, orbicular or irregular ; leaves tubular, semicylindrieal, 
above cylindrical, rigid, fragile, dark green ; spores large, covered 
with coarse farinaceous tubercles, uregularly roughened, scarcely 
reticulated. 
2. I. Engelmanni, mihi, Emersed; rhizoma large, similar to the 
preceding ; leaves longer, more slender, soft, light yellowish-green ; 
sheaths elongated (longer than broad); sporangia longer, spores 
somewhat smaller, coarse, farinaceous, reticulated. 
3. I. riparia, Engelm. MSS. Emersed, rhizoma small (orbicu- 
lar?); leaves slender, soft, yellowish green, sheaths short (broader 
than long); sporangia smaller, spores as large as in the foregoing 
one, very neatly and minutely farinaceous and reticulated. 
. I. setacea, Rosc. Emersed; rhizoma subglobose, regularly 
trilobed ; leaves subulate, somewhat triquetrous, soft, yellowish- 
teen ; spores as large as in the foregoing ones, minutely farina- 
ceous, not reticulated nor tuberculate. poe 
5. I. flaccida, Shuttlew. Submersed ; rhizoma small ; leaves 
very long, slender, flaccid, yellowish-green ; spores very small, 
minutely pulverulent, not reticulated. aa Asa 
The first, Z. lacustris, has been found only in middle and 
northern Europe. — It is distinguished from all others by its thick- 
er, stiffer, dark green (when dry, blackish green) leaves, and large 
Spores, which are covered with an irregular granulation. The 
izoma sometimes measures one inch in diameter. The leaves 
- are mostly straight, and 6 to 8 inches long ; a variety with shorter 
leaves (2 to 3 inches long) which are recurved at the tip rarely 
occurs, probably in shallow water, as the leaves never rise above 
the surface. ~~ | . eke ak 
I. Engelmanni has been distyibuted by Dr. E. to many cor- 
respondents as J. lacustris var. microspora. Tt was afterwards 
distinguished by him as a species, and named J. microspora ; but 
as this name is not sufficiently characteristic, the spores being not 
much smaller than those of J. lacustris, and other species having 
of its discoverer. While J. lacustris inhabits, at least in the 
centre of Eur ; co) 
