39 
closely to the European Р. acutifolius, Link, to which in these 
respects it bears a close resemblance. 
A rare species growing in pools and ponds, and so far as 
known, peculiar to the United States. Lake Cayuga and near Free- 
ville, N. Y. (Dudley); Pine Plains, N. Y. (Hoysradt); Manistee, 
Mich. (Hill, Morong); Ashtabula, Ohio (НШ). (Plate XLVI.) 
23. POTAMOGETON FOLIOSUS, Raf. Med. Rep. 2d Hex. v. 354 (1808). 
P. gramineus ? Mx. Fl. i. 102 (1803), not L. 
P. pauciflorus, Pursh, Fl. i. 121 (1814). 
Pursh’s name, which this species has borne so long, must be 
surrendered, not only because it had been antedated by that of Raf- 
inesque, but also because it had been used by Lamark as long ago 
as 1778 (Fl. Franc. iii. 209, No. 798) as a synonym of P. densus, L. 
A variable species peculiar to North America. Stems flat- 
tened, much-branched, 1 to 3 feet high. Leaves 1-2 inches long 
and %-1 line wide, acute, 3-nerved, not glandular at the base. 
Very delicate forms are found, especially near the Atlantic coast, 
which are scarcely more than 6 inches in height, the stems fili- 
form, the leaves not over 8 lines long by М line wide, the lateral 
nerves obscure or even obsolete. From this it rises into the 
coarser forms which are more common inland and towards the 
west. Stipules white, hyaline, obtuse, sometimes acute, 6-10 lines 
long. Peduncles more or less club-shaped, erect, about % inch 
long. Spikes about 4-flowered. Fruit impressed with a shallow 
pit on each side when young, but even when fully mature, lenticu- 
lar, or nearly orbicular, 34—1 line in diameter; 3-keeled on the 
back, the middle keel winged, sinuate-dentate, often with project- 
ing shoulders or teeth at each end; face strongly angled or arched, 
sharp or alate, often with a sharp, projecting tooth at the base; 
style nearly apical, straight or recurved; embryo curve complete, 
the apex nearly touching the basal end. The fruit rarely ap- 
proaches that of P. pusillus, being obliquely obovate, about 1 line 
long and 3% line wide, the wing on the middle keel narrow and 
not dentate, but still it may always be distinguished by being more 
or less crested. This species is also in very rare cases furnished 
with reproductive buds and minute glands like those of pusiKus. 
Var. NIAGARENSIS (Tuckerman) A. Gray, Man. ed. 2. 435 (1856). 
P. Niagarensis, Tuckerm. Am. Jour. Sci. 2 ser. vii. 354 (1849). 
