488 NAIADACE.E. (pOi'DWEED FAMILY.) 



shining ; fruit roundish and compressed, voiik obtuse margins, slightly heeled; em- 

 bryo circularly incurved above. — Ponds: not common. Aug., Sept. (Eu.) 



Var. minor, Nolte. Smaller; upper leaves distinctly petioled and sometimes 

 emersed, the others subsessile, all usually numerous, undulate and shining. 



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

 sessile, lanceolate, acuminute, crisped, not shining ; fruit larger, distinctly keeled; 

 nutlet thick and hard. — Saltonstall's pond, East Haven, Connecticut, 1850. 



13. P. prselongUS, Wulfen. Stem very long, branching, flexuous ; leaves 

 lance-oblong or lanceolate (sometimes 7' long), half-clasping, obtuse with a boat- 

 shaped cavity at the extremity, thence splitting on pressure ; stipules scarious, 

 very obtuse; spikes rather loose-flowered; peduncles very long (sometimes reach- 

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

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

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

 Superior. Sept., Oct. — Stem white : foliage bright green. (Eu.) 



14. P. perfoliatUS, L. Stem branching ; leaves orbicular, ovate or lanceo- 

 late from a cordate-clasping base, usually obtuse and often minutely serrulate ; 

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

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



Var. lanceol&tus. Larger; leaves long-lanceolate from a cordate-clasping 

 base and acuminate, wavy, 3' to sometimes 4.j' long ; peduncles thickened upwards. 

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



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

 tuse, serrulate, crisped-wavy, 3-nerved ; fruit long-beaked; upper portion of the em- 

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

 Penn., and New Jersey, Tatnall, Porter, Meehan. June, July. (Eu.) 



§ 3. Angcstifolii. Leaves all submersed and similar, mostly membranaceous and 

 sessile, linear or setaceous. (A T o. 16, 17, and 20 are of en gemmiparous, propa- 

 gating by narrow terminal buds detached in autumn.) 



* Stipules free from the sheathing base of the leaf. 



16. P. COmpreSSUS, L. (ex Fries.) Stem branching, icing-fattened; leaves 

 linear and grass-like (commonly 4' by 1^'), abruptly pointed, with many fine and 

 3 larger nerves; stipules (seen young) oblong, very obtuse ; spikes cylindrical, 12- 

 15-flowered, not 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. zosterajfolius, Schumacher.) — Still and slow-flowing waters, 

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



17. P. obtusifolius, Mertens & Koch. Stem fattened, very branching, 

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

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

 flowercd, about 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.) 



