NAIADACE®. 47 
tween the forks of the stem, scarcely exceeding the spike, slender, 
not thickened upwards. Sepals with their lamina roundish-rhombic. 
Fruiting-spike subglobose, dense, few-flowered. Fruit moderately 
large, greenish-olive, considerably compressed, not acuminated, very 
slightly convex on the upper margin, on which there is a large pro- 
minent tooth near the base, half-obovate and bluntly 3-keeled on the 
back, terminated by a rather long slightly recurved beak forming a 
continuation of the upper margin. Plant bright green, retaining its 
colour when dry. 
In ditches and ponds. Rare. Wareham, Dorset (Mr. I. C. Man- 
sel); Amberly, Sussex (Mr. Borrer); Black Sea, Wandsworth Com- 
mon (Mr. W. F. Saunders), and Weybridge, Surrey (Mr. H. C. 
than } to } inch long, the spike much shorter, rarely above } or 3 
Watson); Higham by Norwich, Haddiscome, Brundall and Bucken- 
ham Ferry, Norfolk (Rev. Kirby Trimmer). Probably in some of the 
intermediate counties, but liable to be passed over as P. zosterifolius 
or P. obtusifolius. 
England. Perennial. Summer. 
Stem and foliage very similar to that of P. zosterifolius, but usually 
amore slender plant, with shorter and narrower leaves, 2 to 4 inches 
long by } to 4 inch broad, more gradually acuminated, and with 
stronger stipules. The stem too is usually more branched, and with a 
greater tendency in the branches to become dichotomous. Still when 
the plant is not in flower or fruit, it may easily be passed over as a 
small state of P. zosterifolius. The peduncles, however, are not more 
8 
inch long, with very few flowers. The fruit is smaller, } inch long, 
flatter, with a strong tooth on the upper margin, and is much more 
convex on the back, so that the curve is more than a semicircle; the 
_ beak forms a continuation of the upper margin, and is more than twice 
as long as that of P. zosterifolius. With these differences in the fruit 
_ it is impossible to consider it a subspecies of that plant. 
Sharp-leaved Pondweed. 
French, Potamot a feuilles acuminées. German, Spitzbldttriges Samkraut. 
SPECIES XVUI—POTAMOGETON OBTUSIFOLIUS. Mert. & Koch. 
Pruate MCCCCXYV. 
| Reich. Ic. Fl. Germ. et Helv. Vol. VII. Tab, XXV. Fig. 43. 
_ Billot, F). Gall. et Germ. Exsicc. No. 652. 
P. gramineus Sm. Engl. Bot. No. 2253, and Engl. Fl. Vol. I. p. 235. Hook. & Arn. 
Brit. Fl. ed. viii. p. 480 (non Linn. Herb.). 
Stem 4-sided, slightly compressed, slender, not foliaceous, repeatedly 
_ dichotomous. Leaves all similar, sessile, linear, narrowed towards the 
