POTAMOGETON. 353 



veins occupying the whole surface, spikes cylindrical upon long 

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

 E. B. S. 2685. R. vii. 27. P. cuspidatus Sm., P. compressus 

 Fries. — Ped. 2 — 4 in. long. Spikes 10 — 16-flowered. Inner 

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

 nate or apiculate. — Rivers and lakes. P. VI. E. S. 



13. P. acutifolius (Link); st. flattened, I. linear acuminate joiVA 

 3 principal and many close pai'allel intermediate veins occu- 

 pying the whole surface, spihes ovate about as long as the short 

 ped., Sep. rhomboidal, fr. broadly ^-obovate compressed inner 

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

 E. B. S. 2609. R. vii. t. 26.— Ped. veiy short. Spikes 4—6- 

 flowered. L. gradually acuminate. Styles hooked, continuing 

 the inner edge of the fruit. — Marsh ditches. Sussex. Hertf. 

 Norfolk. P. VI. E. 



14. P. gramineus (L. ?, Sm.); st. slightly compressed with 

 rounded edges, I. linear 3-veined, spikes ovate dense continuous 

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

 keeled.— JS. B. 2253. P. obfusifolius Koch, R. vii. t. 25.— St. 

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

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

 rib, wanting the fine parallel veins of the two preceding species. 

 — Ponds and ditches, rare. P. VI. VII. 



15. P. compressus (L.) ; st. slightly compressed, I. linear 

 5-veined suddenly apiculate, spikes short lax 2 or 3 times shorter 

 than the compressed clavate ped., sep. transversely oval, fr. ob- 

 liquely ovate bluntly keeled. — E. B. 418. R. vii. 24, not Fries, 

 nor Koch. — Lateral veins nearer together and nearer to the 

 margin of the 1. than to the midrib, no intermediate veins. — Like 

 No. 14 rather than 16.— Ditches. P. VI. VII. 



16. P. pusillus (L.) ; St. subterete, I. linear li-veined, spikes 

 short rather lax 2 or 3 times shorter than the slender ped., sep. 

 roundish-reniform, fr. obliquely ovate bluntly keeled. — E. B. 

 215. R. vii. 22. — St. slender. L. narrow, rather acute, without 

 intermediate parallel veins, the lateral veins equidistant between 

 the midrib and margin. Ped. scarcely compressed, not thickened. 

 — [P. rutilus (Wolfg., Fries) has 3-veined attenuate-cuspidate 1., 

 semiterete st., and oblong-elliptical fr. without a keel.] — Ponds 

 and ditches. P. VI. 



[A plant found near Dunstanburgh, Northumberland, by Mr. 

 D. Oliver, is probably P. gracilis (Fr.) which has 1-veined 

 attenuate-cuspidate 1., terete st., and globose-elhptical fr. without 

 a keel.] 



17. P. trichoides (Cham.); st. subterete, I. subsetaceous 1- 



