36 26. Potamogit. 6. FLUVIAT. Pl.end.pL 



10. Poiamogiion pect'inatiim. Featherleafed nverweed. 

 Leaves bristlelike, alternate, the two upper ones opposite, 



parallel, close together, sheathing at the base; spike pe- 

 duncled, thin, often interrupted. 



Poti millefolium, seu foliis gramineis, ramosum, Rail Syn. 150, 14. 

 Potamogetiin pectinatum, Lin. S, P. 183. 

 Fennel-leaf pondweed. 



Rivers and ponds ; perennial ; July. 



Root creeping, originally tuberous ; stem sunk, flowering 

 in still water only, long, filiform, branchy, jointed, whitish; 

 sheath prolonged at top into a small membranaceous li- 

 gula. 



11. Pofamogiton marinum. Sea riverweed. 

 Leaves linear, alternate, 2-rowed, sheathing; margin of 



the sheath scariose ; spike fewflowered, very much inter- 

 rupted. 



Pot. maritimum ramosissiraum grandiusculis capitulis, capillaceo folio, 

 Mali Syn. 130, 13. 



Potamogeton marinum, Lin. S. P. 183. 



Salt water ditches ; perennial ; July. 

 Stem firm, reddish ; joints short ; sheath white ; leaves 

 ©pake and shining. 



12. Potamogiton Vaillantii. Vaillant's riverweed. 

 Leaves linear, alternate, 2-rowed below, sheathing, above 



opposite, subspathaceous ; spike ovate, fewflowered ; Jinwer 

 rather large. 



P. ingeos gramineo folio longiore, Vaill. Paris. 32. 



P. marinum, Teesdale Lin. Tr. 5,43. 



P. Vaillantii, J2oe?jier and Schultze Syst. Veg. 



Stem long, naked below, branchy above, compressed, 

 deeply streaked, yellowish ; lotoer leaves 4 in. long, very 

 narrow ; iipper leaves 2 or 3 in. long ; both light sea-green ; 

 spike 6 or 8-flowered, crowded together. 



13. Potamogiton gramineum. Grass riverweed. 

 Leaves linear, lanceolate, alternate, sessile; stipulce na,v~ 



rower than the leaves ; stem round, rather forked. 



P, gramineum latiusculum, foliis et ramificationibus densissime stipatis, 

 Rail Syn. 149, 10. 



Potamogeton gramineum, Lin. S. P. 184. 



Ditches and rivers ; perennial ; July. 



Plant sunk ; stem slender, bent ; leaves close ; stipules 

 involuto-turbinate ; spikes ovate, fewflowered, close, from 

 the forks of the stem ; peduncles as long as the spike. 



