344 
90. POTAMOGETONE.®. 
10 — 15-flowcved. L. siuldenly acuminate or apiculate. — Rivers 
and lakes. P. VI. E. S. 
13. P. acutifoUus (lAnk) ; st. flattened, /. linear-acuminate witA 
'6 principal ribs and numerous close ])arallel intermediate veins 
occuj)ying the whole surface, spikes ovate about as long as the 
short peduncle, sep. rhomboidal, fr. reniform keeled, style facial. 
— E. B. S. 2009. li. vii. t. 2(1. — Peduncles very short. Spikes 
4 — ()-flowered. L. gradually acuminate. Styles a continuation 
of the straight inner edge of the fr. — Marsh ditches in Sussex and 
Hertfordshire. P. VI. E. 
14. P. gramineus (L.?, Sm.) ; st. slightly compressed with 
rounded edges, 1. linear 3-nerved, spikes ovate dense continuous 
about as long as the short ped., sej). rhoml)oidal, fr. ohovate 
keeled. — E. B. '2253. P. obtusifolius Koch, R. vii. t. 25. — St. 
slender, much branched. Peduncles very short. L. rounded off 
to a slight point at the end, with oblong reticulations next the 
midrib but wanting the numerous parallel nerves of the two pre- 
cechng species. — Ponds and ditches, rare. P. VI. VII. 
15. P. cornpressus (L.); st. slightly compressed, 1. linear 
5- nerved suddenly apiculate, spikes short lax 2 or 3 times shorter 
than their compressed clavate ped., sep. transversely oval, fr. 
obliquely elliptical obtusely keeled. — £. P.418. R. vii.t. 24. not 
Fries, Koch. — Lateral nerves nearer together and nearer to the 
margin of the 1. than to the midrib, no intermediate veins. — 
Resembling the preceding rather than the following. — Ditches. 
P. VI. VII. 
16. P. pusillus (L.) ; st. slightly compressed, 1. linear 3-nerved, 
spikes short rather lax 2 or 3 times shorter than their j)ed., fr. 
obliquely elliptical obtusely keeled. — E.B.'2\5. — St. slender. 
L. narrow', rather acute without intermediate ])arallel veins, the 
lateral nerves equidistant between the midrib and margin. Ped. 
scarcely compressed, not thickened. — [P. trichodes (C. and S.), 
R. vii. t. 21., is closely allied to this but has linear-setaceous 
1 -nerved 1., interrupted spikes and semicircular comj)ressed 
acutely keeled fr. ; also P. rutilus (Wolfg., Fries) w'ith 3-nerved 
attenuate-cuspidate 1., semiterete st., and oblong-elliptical fr. 
without a keel; also P. gracilis (Fries) with I -nerved attenuate- 
cus])idate 1., terete st., and globose-elliptical fr. without a keel.] 
— Ponds and ditches. P. VI. 
**** L. all submersed, alternate, linear, sheathing. 
17 . P.zosteraceus (Fries?); 1. linear acuminate 3-nerved with 
connecting veins, spikes interrupted, fr. (large) roundish-obovate 
rounded on the back with a prominent keel \s\\ci\ dry. — Fries (Sum- 
ma. 216.), R. vii. t. 20? (1. 5-nerved).— Lateral nerves of 1. sub- 
