POTAMOGETON. 343 
of the inner edge of the fr. which has a tooth near the base.— 
Marsh ditches in Sussex, Hertfordshire and Norfolk. P. VI. E. 
14, P. gramineus (L.?, Sm.); st. slightly compressed with 
rounded edges, J. linear 3-nerved, spikes ovate dense continuous 
about as long as the short ped., sep. rhomboidal, fr. obovate 
keeled.— HE. B. 2253. P. obtusifolius Koch, R. vii. t. 25.—St. 
slender, much branched. Peduncles very short. L. rounded off 
to a slight poimt at the end, with oblong reticulations next the 
midrib but wanting the numerous parallel nerves of the two pre- 
ceding species.—Ponds and ditches, rare. P. VI. VII. 
15. P. compressus (L.); st. slightly compressed, J. linear 
5-nerved suddenly apiculate, spikes short lax 2 or 3 times shorter 
than their compressed clavate ped., sep. transversely oval, fr. ob- 
liquely oval obtusely keeled.—E. B. 418. R. vii. 24, not Fries, 
nor Koch.—Lateral nerves 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, 1. linear 3-nerved, spikes 
short rather lax 2 or 3 times shorter than their ped., sep. roundish 
reniform, fr. obliquely oval obtusely keeled.—H#. B. 215. R. vii. 
22.—St. slender. L. narrow, rather acute without intermediate 
parallel veins, the lateral nerves equidistant between the midrib 
and margin. Ped. scarcely compressed, not thickened.—[P. ru- 
tilus (Wolfg., Fries) has 3-nerved attenuate-cuspidate 1., semite- 
rete st., and oblong-elliptical fr. without a keel; P. gracilis (Fries) 
has l-nerved attenuate-cuspidate 1., terete st., and globose-ellip- 
tical fr. without a keel.|—Ponds and ditches. P. VI. 
17. P. trichoides (Cham.); st. subterete, 1. subsetaceous 1- 
nerved finely pointed, spikes short lax long-stalked, fr. semicir- 
cular obscurely keeled, inner edge with a tooth near its base.— 
Linnea ii. t. 4. R. vii. 21.—St. very slender a little thickened 
below the joinings. L. not transversely vemed. Floral stip. large. 
Ped. not thickened. Sep. roundish, stalked. Fr. often verrucose 
on the back and with a tubercle on each side at its base when 
fresh. —Bixley near Norwich. P. VII. VIII. 
*ekk T) all submersed, alternate, linear, sheathing. 
18. P. fladellatus; lower 1. broadly linear abruptly apiculate 
or acuminate 5-nerved with transverse veins, floating 1. narrow 
acute 3-nerved, fr. (2 lmes long) roundish-obovate rounded on 
the back, nut with a prominent keel—P. zosteraceus Bab. (not 
Fr.).—Floating st. branched and spreading like a fan. Broad 
lower 1. usually decayed at the time of flowering. Lateral nerves 
of upper 1. at the margin, of lower |. distant from it. Spikes 
