96 TETRANDRIA, TETRAGYNIA. 



hybridum /3 3. P. upper leaves petiolated, elliptical, attenuated 

 Gmei. & mx. at b ot h enc | s . lower ones crowded, sessile, linear. 



— mud. 



P. heterophyllum, 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. 



diversifoli- 

 ura, Barton. 



4. P. plant small, delicate : stem filiform, emersed ; 

 leaves floating, elliptical, petiolated, half an inch 

 long, six nerved ; submersed leaves, sessile, fili- 

 form, long ; spikes numerous, small, depressed, 

 in the axils of the leaves. — Barton, Prod. Fl. 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 minima grows, on the 

 borders of the Schuylkill, a mile or two this side of the Falls. 

 Hitherto these are the only places where 1 nave seen it, and, 

 as I have carefully searched almost every pond near Philadel- 

 phia for it, conclude it is rare. Perennial. July. 



perfoiiatum. 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. 



