I [11 



Potamogeton.'] CV. NAiADACEiE. 481 



3-nerved. Judging from the specimens we have seen in herbaria, 

 P, gramineus is more common than P. pusiUus jS., while P, pusillus 

 a. is more common than either of the others. 



7. P. acutifolius Jjink (sharp-leaved P.);, stem compressed, 

 leaves linear acuminate with 3 principal and numerous close 

 parallel intermediate nerves occupying the whole surface, 

 spikes oval compact about equalling in length the short pe- 

 duncle. Hook in E. B. S. t. 2609. 



Rare? Hitherto only found in marsh-ditches at Amberley, Hen- 

 field, and Lewes, Sussex. It. 7. — The numerous closely placed 

 parallel nerves well distinguish this and the following species from 

 their congeners, 



8, P. zostercefolius Solium. (Grass-wracJi-like P.) ; stems 

 compressed, leaves broadly linear acute with 3 principal and 

 numerous close parallel intermediate nerves occupying the 

 whole surface, spikes cylindrical upon long peduncles. ^. JB, 

 t. 2685. P. cuspidatus Schrad,: JE, FL v. i. p. 234. 



Rare ? Rivulet at Hovingham, Yorkshire ; River Sow, at Staf- 

 ford. Lakes of Rescobie and Forfar. IjL. 7. — Larger than the 

 last, with peduncles 3 — 4 inches long, and spikes cylindrical, an inch 

 in length. 



**** Leaves alternate, ovate, lanceolate or ohloiig, all pellucid and sub- 

 merged; stipules free, 



9. P. crispus L. (curly P.) ; stem compressed, leaves lanceo- 

 late waved and serrate 3-nerved sessile, fruit beaked. E. B. 

 t 1012. 



Ditches and rivers, frequent. 1/.. 6, 7. — Peduncles elongated, not 

 thickened upwards. 



10. P. perfolidtus L. (perfoliate P.) ; leaves cordate-ovate 

 sessile and amplexicaul 7-nerved with smaller Intermediate 

 nerves. E. B. t. 168. 



Ditches and lakes, frequent. 1/.. 7. — Peduncles rather short, 

 thick, not swollen upwards. Spikes oblong-ovate. 



IL P. prcelongus Wulf. (long-stalked P.); leaves entire 



narrow-oblong semiamplexicaul obtuse and cymbiform at the 



end, with 3 principal and several lesser parallel nerves arising 



from the base connected by reticulations, stipules not winofed, 



peduncles elongated, spikes cylindrical many-flowered. E, B. S. 

 t. 2858. 



Lakes and pools. Ditch by Caversham bridge, near Reading; 

 River Sow, at Stafford; Gormere, Malham, Yorlishlre. Berwick- 

 shire; Moss of Litie, Nairnshire; Lochleven, Kinross-shire. Ij.. 



\ 





This is best distinguished by its oblong (by no means elliptical) 

 leaves, nerved from the base, where they are semiamplexicaul, and 



Y 



