96 
TETRANDRIA, TETRAGYNIA- 
hybridum /3 3. P. Upper leaves petiolated, elliptical, attenuated 
Gmei. & Mx. both ends i lower ones crowded, sessile, linear. 
—Willd. 
P. heteruphyllum, Willd. and Pursh. 
P. porcatum, Muhl. 
Furrow-leaved Pond-weed. 
Upper leaves an inch and a half long, lower ones linear. 
In dirty ditches, plashes, and pools. Very rare. I have only 
found it near Lemon. Hill, at low tide, on the Schuylkill. 
Perennial. June to August. 
nm^Slnon plant Small, delicate : stem filiform, emersed ; 
leaves floating, elliptical, peiiolated, half an inch 
long, sixmerved ; submersed leaves, sessile, fili- 
form, long ; spikes numerous, small, depressed, 
in the axils of the leaves.— Prod. FI. Ph, 
Probably P. setaceum of Pursh. 
Different-leaved Pond-weed. 
This singular little species I first discovered in Jersey, near 
Woodbury, where it is abundant, in a pool. I subsequently 
detected it in a pond, where Nuphar mlnjnia grows, on the 
borders of the Schuylkill, a mile or two this side of the Falls. 
Hitherto these are the only places where I have seen it, and, 
as I have carefully searched almost ^very pond near Philadel- 
phia for it, conclude it is rare. Perennial. July. 
perfoliatum. 6. P. leaves cordate-ovate amplexicaule, all sub- 
merged, spike terminal; flowers alternate. — Mich, 
and Willd. 
Icon. fl. Dan. 196. Eng. Bot. 168. 
Leaves transparent ; the whole plant submerged, the spike 
of flowers only floating — In ponds, rivulets, and rivers, fre- 
quent. At low tide, found abundantly on the muddy and gra- 
velly banks of the Delaware, and Schuylkill, on either side- 
Perennial. 
