484 cv. naiadaceyE. \_Potamngeton. 
Ditches and slow streams, in many parts of England. Anglesea. 
Near Glasgow and Forfar ; in the Gady at Premnay, and Aberdeen 
canal, Aberdeenshire. 2f. 7. — This in some situations much re- 
sembles P. lucens. Coriaceous floating leaves nearly as acute as the 
lower ones, differing only in their firmer texture and in being stalked; 
lateral ribs or nerves not separate to the base of the leaf, arising from 
various parts of the central rib, and from 6 — 7 in number on each 
side, 2 of them more evident than the rest; flower-stalk not thickened 
upwards: Wilson. The plant is remarkable for its reddish-olive colour, 
and is perhaps better known by its general aspect, size, and hue, than 
by any character that can be applied to it. 
17. P. plantaginens Ducr. ( Plantain-leaved P.) ; leaves all 
membranous stalked, lower ones oblong, upper elliptical, 
achenes minute obliquely ovate convex on the back when re- 
cent acutely keeled when dry, spike slender cylindrical densely 
flowered, peduncle long not thickened upwards. E. B. S. t. 
2848. P. coloratus Horn. : Cham, et Schl. 1. c. p. 194. 
Deep peaty pits and ditches, probably far from rare in England. 
Oban ; Ferneyrig Loch, Berwickshire. If.. 6,7. — Distinguished from 
P. nutans by its beautifully diaphanous reticulate leaves, none of 
which are coriaceous, and its much smaller fruit. It is more allied 
to P. oblongus, from which, according to Mr. Babington, its leaves, as 
well as the acutely keeled back of the fruit when dry, clearly distin- 
guish it. These characters, however, seem to be of little importance: 
Mr. Bentham unites it along with the next to P. natans. 
18. P. obldngus Yiv. (oblong -leaved P.) ; “leaves all 
stalked, upper ones coriaceous floating oblong-elliptical, lower 
linear-lanceolate, achenes minute with their back always obtuse 
and rounded, spike slender cylindrical densely flowered upon a 
long terete peduncle.” Bab : in E. B. S. t. 2849. P. natans 
i. Mert. et Koch. P. polygonifolius Pourr. : Bab. 
“ Far from uncommon, in wet ditches, small streams, ponds, and 
bogs.” Frequent in Scotland. . 7. — “ It is distinguished from 
P. natans, with which most botanists probably confound it, by the 
form and size of its fruit, as well as by other characters:” Bab. We 
fear the above characters are not constant, for we have examined speci- 
mens where the achenes were decidedly marked on the back with 3 
ridges, the middle one being acute. It is found usually in bogs and 
ditches almost dry in summer, which may explain why the fruit is 
not above haif the size of that of the next species. 
19. P. natans L. ( sharp-fruited broad-leaved P.) ; lower 
leaves linear submembranous or wanting, upper elliptical 
coriaceous floating on long stalks many-nerved distinctly cel- 
lular, fruit (large) keeled at the back. E. B. t. 1822. 
Stagnant waters and slow streams, frequent. 2f. 6, 7. — Very 
variable in general size, and in the shape of its floating leaves, which 
are more or less elongated, sometimes linear-lanceolate, obtuse at the 
