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, f lin. lone. Stagnant peaty water. 

 P. VI. VII. 



4. P. rufescens (Schrad.); 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. JR. vii. 

 32. P. fluitans 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 E.) P. nigrescens Fries? 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 winged, fr. unknown. St. very 

 slender, slightly 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. KirkJ] I. 



6. P. heterophyllus(Schreb.}; submersed L 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. 



