POTAMOGETON. 351 



netted with veins, the upper often almost sessile and nearly 

 orbicular, sometimes slightly cuspidate. Petioles plane-concave 

 above. Spikes long, cylindrical. Anth. -cells nearly parallel. 

 Sep. ovate. Fr. greenish, i lin. Ions. — Stagnant peaty vpater. 

 P. VI. VII. 



4. P. rufescens (Sohrad.); submersed I. lanceolate narrowed 

 at both ends subsessile membranous pellucid entire not apiculate 

 with chainlike network near the midrib, floating 1. subcoriaceous 

 obovate obtuse narrowed into a short petiole, stip. without 

 wings, fr. acutely keeled, peduncles equal. — E. B. 1286. R. vii. 

 32. P. jluitans Sm. — St. simple. Upper 1. alone slightly 

 coriaceous, often tinged with purple, longer than their stalks ; 

 submersed 1. all nearly, if not quite, sessile. Sep. " transversely 

 oval." — Ditches and slow streams. P. VII. 



5. P. lanceolatus (Sm.) ; submersed I. lanceolate narrowed at 

 both ends entire not apiculate with chainlike network near the 

 midrib, floating 1. subcoriaceous elliptic-lanceolate stalked, stip. 



linear-lanceolate acute uppermost broader, fr , peduncles 



equal. — E. B. 1285. (not R.) P. nigrescens Friesl — St. very 

 slender, slightly branched. Floating 1. not always present. 

 Uppermost stip. apparently with 2 stronger dorsal ribs. Fr. 

 unknown.— Streams, rare. P. VII. VIII. E. S. I.? 



[P. sparganiifolius (Laest. ?) ; submersed I. linear narrowed at 

 both ends very long sessile entire not apiculate with many 

 parallel veins next the midrib, floating 1. subcoriaceous lanceolate 

 long-stalked, stip. very long not wiaged, fr. unknown. — St. very 

 slender, shghtly branched. Floating 1. often wanting. Sub- 

 mersed 1. sometimes 2 ft. long, very narrow, few-veined with 

 additional parallel veins closely placed next the midrib. L. very 

 much longer than those of P .lanceolatus and without the chainlike 

 network. — A remarkable plant requiring examination. — In the 

 river at Ma'am, Galway. Mr. T. Kirk.'] I. 



6. P. heterophyllus (Schreb.); submersed I. lanceolate narrowed 

 at both ends sessile denticulate and apiculate, floating 1. subco- 

 riaceous elliptical stalked, stip. broadly lanceolate obtuse with 

 2 stout prominent ribs, lower ones linear-lanceolate, fr. obtuse on 

 the back, peduncles swelling upwards. — E. B. 1285. R. vii. 41- 

 43. P. gramineus. Fries, not Linn. — St. much branched below. 

 Submersed 1. wavy. Lower stip. without the two strong ribs 

 and equally veined, upper ones widely spreading. Dry fr. 

 slightly marked with 3 ridges on the back. — [P. nitens (Weber) 

 has the submersed 1. rounded and clasping at their base.] — 

 Ponds and ditches. P. VI. VII. 



