488, naiadacejE. (pondwef.d familt.) 



ffiinhitj ; fruit ro\m(\hh and compressed, «v7A ohtusr margins, sliuhilji heelid; em- 

 bryo eirciilarly incurviMl aKovc — Ponds -. not common. Aug., Sept. (Eu.) 



Var. minor, Xoltc. Smaller; upper leaves distinctly petioled am\ sometimes 

 emersed, the otlicrs siil)sessile, all usually numerous, undulate and sliinivg. 



Var. ? Connecticutensis. Stem flexuous ; Itaves all submersed, nearly 

 sessile, laiieeulale, acumindte, crisped, not shininrj ; fruit larr/rr, diatiiictli/ keeled; 

 nutlet thiek and hard. — Saltonstall's pond, East Haven, Conneeticut, 18.50. 



13. P. pi*8el6ngUS, Wulfen. Stem very long, brandling, flexuous ; haves 

 lanee-oblong or laneeolate (sometimes 7' long), hdlfclasjiinfj, obtuse with a boat- 

 s'iii/>ed cavil ij lit the extremity, thenec splitting on pressure; stipules searious, 

 very obtuse; sj)ikes rather loose-flowered; peduncles very Ion;/ (sometimes reach- 

 ing 20') ; fruit obliquely obovate, compressed, sliarjilij keeled when dry ; style ter- 

 minating the nearly straight iace ; curve of tbc embryo oval and longitudinal. — 

 Ponds and large rivers, E. New England, and along the Great Lakes to Lake 

 Superior. Sept., Oct. — Stem wbite : foliage brigbt green. (Eu.) 



14. P. pei'foliatUS, L. Stem i)ranehing; leaves orbicular, ovate or lanceo- 

 late from a cordute-claspiiifj base, usually obtuse and often minutely serrulate; 

 peduncles short, cylindrical ; fruit irregularly obovate, obtusely manjintd; embryo 

 incurved in an oval. — Ponds and slow streams : common. Sept., Oct. (Eu.) 



Var. laneeolatus. Larger; leaves long-lanceolate from a cordate-elnsping 

 base and acuminate, wavy, 3' to sometimes 4.^' long ; peduncles thickevcd upivurds. 

 — Along the Great Lakes. — This form seems peculiarly American. 



15. P. crispus, L. Stem compressed; leaves linear-oblong, half-clasping, ob- 

 tuse, serrulate, crisped-wavij , 3-neived ; fruit long-beaked ; upper portion of the em- 

 bryo incurved in. a large circle. — Flowing and stagnant waters, Delaware, 

 Penn., and IsevsH^sey, Tatnall, Porter, Meehan. June, July. (Eu.) 



§ 3. Angl'STIFOHI. Leaves all submersed and similar, mostly membranaceous and 

 sessile, linear or sfitareous. (xVo. 16, 17, and 20 are of en gemmiparous, propa- 

 gating by narrow terminal buds detached in autumn.) 



* Slifiiiles free from the sheathing base of the leaf. 



16. P. COmpressus, L. (ex Fries.) Stem branching, wiug-flatlened ; leaves 

 linear and grass-like (commonly 4' by l.j'), abruptly pointed, with many fne and 

 5 larger nerves; stipules (seen young) oblong, very obtuse ; sjtikes cylindrical, 12- 

 1.5-flowered, 7iot half as long as the peduncle; fruit obliquely obovate, somewhat 

 keeled and with slight teeth on the back, the sides not impressed, the face arch- 

 ing and terminated by the short style ; summit of the large embryo lying transverse 

 to the fruit. (P. zosterrefolius, Schumacher.) — Still and slow-flowing waters. 

 New England to Penn. and Wisconsin : not common. Aug., Sept. (Eu.) 



17. P. obtusifdlius, Mertens & Koch. Stem flattened, very branching, 

 leaves linear, tapering towards the base, obtuse and mucronate or very acute, 3- 

 (rarely h-) nerved; stipules elongated, very obtuse; spike orate, continuous, 5-8- 

 flowcred, oLout the length of the peduncle ; fruit oval, apiculate with the style, not 

 keeled when fresh, upper portion of embryo coiled inward and lying transverse to 

 the fruit. — Slow streams and ponds: very rare : Dillerville swamp, near Lan- 

 caster, Penn., Prof. Porter. Swamp of Beaver pond, near Central mine, and 

 floating in Gratiot Lake, N. Michigan. Sept., Oct. (Eu.) 



