| NAIADACEA. 27 
Submerged leaves bright green, floating leaves dull green, often 
purple beneath. 
In ponds and ditches. Common, and generally distributed in 
'England. Rather local in Scotland, where it appears to be absent from 
the extreme north. Common and generally distributed in Ireland. 
England, Scotland, Ireland. Perennial. Summer, Autumn. 
Rootstock extensively creeping, and sending up stems varying in 
length according to the depth of water in which the plant grows, which 
is rarely less than one or two feet and often greater. Submerged 
leaves resembling the petioles of the floating leaves, channeled above ; 
floating leaves 2 to 4 inches long, differing from those of all the British 
Potamogetons in having the coriaceous substance continued a little 
way down the petiole, with a fold at the base, which, when the leaf is 
pressed flat, forms a ridge on each side of the midrib. When held 
against the licht, the transverse veins are visible, but not distinctly so, 
on account of the thickness of the substance of the leaf. Stipules 
-scarious, those of the upper leaves very long, at length fibrous, from 
the decay of the tissue connecting their ribs. Peduncle usually about 
as long as the spike, stout. Fruiting spike 1} to 3 inches long. Fruit 
nearly } inch lone, when fresh greenish-olive, obtuse on the back 
until it dries, when a keel is developed. 
Koch and Grenier say that before flowering the submerged leaves 
have a narrow lamina, which decays by the middle of May. I have 
never seen this, though I have looked for such leaves at all seasons. 
Floating Pondweed. 
French, Potamot nageant. German, Schwimmendes Samlcrautgewtchse. 
SPECIES IL—POTAMOGETON POLYGONIFOLIUS. Powrret. 
Prate MCCCC. 
| Reich. Ic. Fl. Germ. et Hely. Vol. VII. Tab. XLIV. Figs. 79 and 80. 
P. oblongus, Viv. Bab. in Engl. Bot. Sup. No. 2849. Fries, Summ. Veg. Scand. 
pp. 68 (67), and 213. Koch, Syn. Fl. Germ. et Helv. ed. ii. p. 775. 
Stems round, simple or nearly so. Lower leaves alternate, submerged, 
shortly stalked, oblanceolate or elliptical or strapshaped-elliptical and 
-membranous—or longly-stalked, subcoriaceous, rising out of the water, 
and oblong-ovate or oval; uppermost leaves opposite, floating or rising 
out of the water, of the same texture as the whole of the rather short 
petiole, oval or oblong or elliptical, subcoriaceous, with numerous longi- 
tudinal ribs connected by cross veins, which are very conspicuous if the 
dried leaf be held against the light, when minute arcolation is scarcely 
perceptible all over the leaf between the veins. Stipules large, not 
winged on the back, subfibro-scarious. Peduncles axillary, slender, 
E 2 
