NAIADACE^. (PONDWBED FAMILY.) 435 



Var. NiagarensiS (P. Niagarensis, Tudcerm.), from the brink of the cat- 

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

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



7. P. COmpr^SSUS, L. ex Fries. Stem very fM, almost as wide as tlie 

 narrowly linear abruptly pointed leaves; spikes cylindrical, 10 - l5-Jloioered ; fruit 

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

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

 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 pdlucid, 



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



8. P. perfoliatllS; L. Leaves clasping by a heart-shaped base, ovate or 

 ovate-lanceolate, sometimes round-ovate, obtuse; spikes rather few-iiowered ; yrui'i 

 rounded on tlie bach — 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.) 



9. P. prSBl6ngns, Wulf. Leaves elongated-oblong, obtuse at both ends, 

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

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

 wlien 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 base or 

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

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

 ingly branched. 



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

 oblong-oval to broadly lanceolate, undulate, somewhat petioled ; tlie 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. f floitans. 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 Iiere I would 

 refer P. pulcher? and P. amplifolius, Tuckenn. P. rufescens, Schroder, is a 

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

 obmtus, Wood) or with them, of a brownish or reddish tin'ge, and verging to the 

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

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

 keeled fi-uit. 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 fniit differs in the strength of the keels, &c. But I have not been 

 able to limit them. (Eu.) 



11. P. natans, L. Immersed leaves narrowly lanceolate or linear and 

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

 leaves long-petioled, elliptical or ovateK)blong, sometimes slightly hcart-shsipcd 



