naiapace.t;. 45 



towards the ajiex, 3- to 5-ribbecl, the ribs connected by transverse 

 veins only at the aj^ex. Stipules absent, except from tlie pairs of 

 leaves from which peduncles spring. Peduncles terminal from the 

 forks of the stem, short, slender, not thickened upwards, sharply re- 

 curved in flower and fruit. Sepals with the lamina ovate-deltoid. 

 Fruitmg-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 generallj' dis- 

 tributed in England. Pare 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. 



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 serre. German, Diclithldttriges SamJcraut. 



Section III.— GRAMINIFOLII. 



Leaves alternate, the upper ones opposite, all similar, sessUe, linear, 

 with flat vernation, 1- to 5-ribbed, with few transverse veins. Stipules 

 free. Pedimcles terminal and pseudo-lateral. Spikes few-flowered, 

 short, dense. 



SPECIES XVI.— POTAMOGETON ZOSTERIPOLIUS. Sdmm. 



Plate MCCCCXV. 



Beich. Ic. ¥]. Germ, et Helv. Vol. VH. Tab. XXVII. Fig. 45. 



P. compressus, Fries, Nov. Fl. Suec. p. 44, and Summ. Veg. Scand. pp. 68 (G7) and 



215. Koch. Syn. Fl. Germ, ct Hclv. ed. ii. p. 779. Gren. & Godr. Fl. de Fr. 



Vol. in. p. 316 (non Lhm. Herb.). 

 P. cuspidatns, Sm. Engl. Fl. Vol. I. p. 234. 



Stem flattened, broad, and subfoliaceous, scarcely dichotomous. 



