POTAMOGETON. 383 



veins adjoining the midrib. Peduncles 6 — 12 in. long. Spikes 

 1 — 2 in. long. — Rivera and ditches, rare. P. V. VI. E. S. I. 



16. P. perfolidtus (L.) ; st. round I. pellucid cordate-ovate 

 clasping not hooded, fr. rounded on the back when fresh keeled 

 when dry, peduncle equal. — -E. B. 168. iJ. vii. 29. — St. long, 

 slightly branched, rather dichotomous at the top. Peduncles 

 rather thick and short. Spikes short. — ^Lakea and streams. 

 P. VII. E. S. I. 



16. P. cris'ptis (L.) ; st. compressed, I. pellucid linear-ohlong 

 blunt sessile serrate wavy, fr. with a long leak keeled on the 

 back when dry, peduncle equal. — E. B. 1012. P. vii. 29 — 30. 

 — St. much branched. Ped. long. Spikes few-flowered. Beak 

 as Ion? as the nut. L. usually crisped at the edges, occasionally 

 flat (P. serratus Huds.). — Ditches and streams. P. VI. E. S. I. 



*** L. all submersed, alternate, Unear-ligulate ; stipules free. 



17. P. zosterifdlius (Schum.) ; st. flattened, I. linear-acumi- 

 nate wit7i 3 principal and many close parallel intermediate veins 

 occupying the whole surface, spikes cylindrical upon ' long ped., 

 sep. transversely oval, fr. obovate keeled, style terminal. — 

 -E B. 8. 2685. P. vii. 27. P. cuspidatus Sm., P. compressus 

 Fries, Hook. — Ped. 2 — 4 in. long. Spikes 10 — 15-flowered. 

 Inner edge of fr. rounded ; faces a little convex. L. suddenly 

 acuminate or apiculate. — Rivers and lakes. P. VI. E. S. I. 



18. P. acutifdlius (Link) ; st. flattened, I. linear acuminate 

 loith S principal and many close 'puraJlel intermediate veins occu- 

 pying the whole surface, spikes ovate about as long as tlie short 

 ped., sep. rhomboidal, fr. broadly j-obovate compressed i7iner 

 edge straight with a tooth near its base keeled, style facial. — 

 i;. B. S. 2609. P. vii. t. 26.— Ped. very short. Spikes 4—6- 

 flowered. L. gradually acuminate. Styles hooked, continuing 

 the inner edge of the fruit. — Marsh ditches, rare. P. VI. E. 



19. P. obtusifdlius (Koch) ; st. slightly compressed with 

 rounded edges, I. linear S-veined, spikes ovate dense continuous 

 about as long as the short ped., sep. rhomboidal, fr. obovate 

 keeled.— P. vii. t. 25. P. gramineus Sm., K B. 2253.— St. 

 slender, much branched. Peduncles very short. L. rounded 

 off to a slight point at the end, with oblong network near the 

 midrib, wanting the fine parallel veins of the two preceding 

 species. — Ponds and ditches, rare. P. VI. VII. E. S. I. 



20. P. mucrondtus (Sehrad.) ; st. slightly compressed, I. linear 

 b-veined suddenly apiculate, spikes short lax i or f shorter than 

 the compressed clavateped., sep. transversely oval, fr. obliquely 



