NAIADACE.E. (PONDWEED FAMILY.) 435 



Var. Niagai'ensiS (P. Niagarensis, TucJcerm.), from the brink of the cat- 

 aract of Niagara, appears likely to be a larger-leaved and more rigid state of 

 this species; the stipules more conspicuous, the leaves sometimes 1^" wide. 



7. P. COHJpreSSliS, L. ex Fries. Stem very flat, almost as wide as the 

 narrowly linear abruptly pointed leaves; spikes cylindrical, 10-15-flowered ; fruit 

 obtusely keeled. (P. zostersefolius, Schum.) — Ponds, New England to Penn., 

 Wisconsin, and northward. — Stems 2° -4° long. Leaves 3' -6' long, 1^" 

 wide, minutely many-nerved and with a midrib or 3 nerves more conspicuous, 

 perfectly entire. (Eu.) 



* * Leaves ovate or oblong, with a clasping base, all immersed, thin and pellucid, 

 Z-many-nerved, and with cross veinlets : stems more or less branched. 



8. P. pcrfi>liatu§, L. Leaves clasping by a heart-shaped base, ovate or 

 ovate-lanceolate, sometimes round-ovate, obtuse; spikes rather few-flowered ; fruit 

 rounded on the back. — Ponds and rivers; common. — Leaves l'-2' long, flat ; 

 or, in the longer and ovate-lanceolate American forms, inclined to be acute and 

 more or less wavy or crisped. (Eu.) See Addend. 



9. P. fii'celdllg'IlS, Wulf. Leaves elongated-oblong, obtuse at lioth ends, 

 half-clasping by the sessile base ; peduncles often much elongated (in deep water 

 6'- 12' long) ; spike cylindrical, many-flowered ; fruit strongly heeled on the back 

 when dry. — Rivers and ponds, New England to Wisconsin and northward. — 

 Stipules wingless. Leaves 1' or less wide, 2' -7' long. (Eu.) 



* * # Leaves not clasping, mostly of 2 sorts ; the immersed ones acute at the l>ase or 

 tapering into a petiole, thin and pellucid, many-nerved and reticulated by cross-vein- 

 lets, the floating ones somewhat coriaceous and long-petioled : stems simple or spar- 

 ingly branched. 



10. P. lliccns, L. Immersed leaves ample (3' -9' long), varying from 

 oblong-oval to broadly lanceolate, undulate, somewhat petioled; the united stip- 

 ules 2-winged or keeled on the back ; peduncle thickened, especially upwards ; spike 

 elongated, dense ; fruit 1 - 3-keeled on the back. — The proper P. lucens usually 

 wants the floating leaves, and is common in deep water. (Eu.) 



Var. ? fluif ailS. Uppermost leaves floating on distinct but rarely very long 

 petioles, varying from oblong-lanceolate and acute at each end to ovate and 

 obtuse or heart-shaped (2'-4' long). P. fluitans, Roth., &c. ; and here I would 

 refer P. pulcher ? and P. amplifolins, Tuckerm. P. rufescens, Schroder, is a 

 narrow-leaved form, with smaller fruit, &c., either without floating leaves (P. 

 obrutus, Wood) or with them, of a brownish or reddish tinge, and verging to the 

 larger forms of No. 12. — Mostly in rather deep water; common northward. 

 Distinguished from P. natans by its broader and large immersed leaves, and 

 keeled fruit. Probably P. fluitans may be separated from P. lucens, and perhaps 

 several species with floating leaves may be here confounded ; the forms are di- 

 verse, and the fruit differs in the strength of the keels, &c. But I have not been 

 able to limit them. (Eu.) 



11. P. u:\taaas, L. Immersed leaves narrowly lanceolate or linear and 

 mostly long petioled ; the thin blade early decaying, sometimes wanting ; floating 

 leaves long-petioled, elliptical or ovate-oblong, sometimes slightly heart-shaped 



