JC TETRANDRIA.— TETRAGYNIA. 



132. POTAMOGETON. Naiades. Pond-weed. 

 * Upper leaves floating. 



I. P. natans : upper leaves floating; coriaceous, ob- 

 long-ovate, on long petioles, (subcordate :) lower 

 ones membranaceous, lanceolate, tapering to afoot- 

 stalk. 

 HAB. Lakes and slow streams. July — Aug. V-. Upper 

 leav. 2 — 3 in. long, 2 broad, nerved ; spike greenish. 



1. P.Jluitans: upper leaves floating, coriaceous, ob- 

 long-lanceolate, petiolate, tapering at the base, 

 lower ones linear, sessile. 

 HAB. Ponds and slow streams. July — Aug. V-. 

 Upper leav. 3 in. long* 1 broad, olive-green ; pedunc. 

 thick. 



). P. heterophyllum : upper leaves floating, petiolate. 

 elliptical ; lower ones sessile, crowded, linear. 

 HAB. Ponds and slow streams. Aug. U . Half the 

 size of the preceding ; submerg. leav. very narrow. 



I. P. diversifolium : upper leaves floating, elliptical, 

 petiolate, 5-nerved ; inferior ones filiform ; spike 

 axillary, almost sessile, few-flowered. 

 HAB. Ponds and slow streams. June. U . Stems 

 filif. ; upper leav. not an in. long ; spik. 4 — 6 fi. 



* * Leaves all submerged. 



j. P. perfoliatum : leaves amplexicaul, cordate, ovate. 

 HAB. Rivers and lakes. Aug. Stem dichot. ; leaves 

 1 in. long, subpelluc. ; spike few-fl. 

 £. P. lucens: leaves ovate-lanceolate, petiolate. 



HAB. Rivers and lakes. Aug. V-. Stem terete; 

 leav. 2 — 3 in. long, pelluc. reticul. ; spik. cylind. 

 7. P. crispum: leaves lanceolate, tapering, sessile, 

 undulate and serrate. 

 HAB. Lakes. Aug. 1/. Stem subcomp. ; leav. lj in. 

 long; spik. 8 — 10 Jl. 

 <. P. compressum: leaves linear, obtuse, sessile ; stem 

 compressed. 



HAB. Slow streams. July — Aug. 11 . Stem much 

 branch., thick; pedunc. compress. ; spikA — §fl. 



