NAIADACE®. 45 
towards the apex, 3- to 5-ribbed, the ribs connected by transverse 
veins only at the apex. Stipules absent, except from the pairs of 
leaves from which peduncles spring. Peduncles terminal from the 
forks of the stem, short, slender, not thickened upwards, sharply re- 
euryed in flower and fruit. Sepals with the lamina ovate-deltoid. 
Fruiting-spike ovoid, 2- to 6-flowered. Nuts pale olive, rather large, 
suborbicular-obovate, compressed, convex on the upper margin, rounded 
and sharply keeled on the back, with a short recurved terminal beak. 
Plant bright green, retaining its colour when dry. 
In ditches, ponds, and slow streams. Common, and generally dis- 
tributed in England. Rare in Scotland, where it is known to occur 
only in the counties of Edinburgh, Haddington, and Lanark. Local, 
and rare in Ireland, and confined to the southern half of the island. 
a ae ee ee SE 
England, Scotland, Ireland. Perennial. Summer, Autumn. 
Rootstock sending up brittle stems 3 to 18 inches long, with short 
internodes and dichotomous branching. Leaves increasing in size up- 
wards, the largest } to 1} inch long, generally more or less recurved, 
and slightly folded. Peduncles shorter than the leaves, usually 4- 
flowered. Nuts olive, about } inch long. 
This cannot be confounded with any other species, as the leaves 
are all sessile, opposite, and submerged, and without stipules, except 
those at the forks of the stem, which are accompanied by membranous 
stipules adhering to the leaf at the base, and with an oblong free 
portion. 
Opposite-leaved Pondweed. 
French, Potamot serré. German, Dichtblattriges Samkraut. 
Saction IIT.—GRAMINIFOLII. 
Leaves alternate, the upper ones opposite, all similar, sessile, linear, 
with flat vernation, 1- to 5-ribbed, with few transverse veins. Stipules 
free. Peduncles terminal and pseudo-lateral. Spikes few-flowered, 
short, dense. 
SPECIES XVL—POTAMOGETON ZOSTERIFOLIUS. Schun. 
Prare MCCCCXYV. 
_ Reich. Ic. Fl. Germ. et Helv. Vol. VII. Tab. XXVII. Fig. 45. 
_ P. compressus, Fries, Noy. Fl. Suec. p. 44, and Summ. Veg. Scand. pp. 68 (67) and 
215. Koch. Syn. Fl. Germ. et Hely. ed. ii. p. 779. Gren. & Godr. Fl. de Fr. 
Vol. TIT. p. 316 (non Linn. Herb.). 
_ P. cuspidatus, Sim. Engl. Bot. Vol. I. p. 234. 
Stem flattened, broad, and subfoliaceous, scarcely dichotomous. 
