NAIADACE^E. 29 



Yar. 7 is found on .ilmost every heath, and is the commonest form 

 of Potamogeton in the whole country, extending north to Orkney. 

 Tliis has the leaves all similar, and often grows in mud without any 

 water. 



In Glen Devon, near Dollar, I have found a form near var. 7, with 

 the npi)er leaves nearly round, and deeply cordate at the base, and 

 with larger, blunter, and more membranous stipules than in the ordi- 

 nary form. 



Oblong-leaved Pondweed. 



German, Ldngliches Samkraulgewdchse, 



SPECIES III.-POTAMOGETON PLANTAGINEUS. Ducros. 



Plate MCCCCI. 



BeicTi. Ic. Fl. Germ, et Helv. Vol. VII. Tab. XLV. and XL VI. Figs. 82 to 85. 



Billof, Fl. Gall, et Germ. Exsicc. No. C51. 



P. coloratns, Wallr. Fries, Suram. Veg. Scand. p. 68 (67). 



P. Hornemanni, Meyer. Koch, S}ti. Fl. Germ, et Helv. ed. ii. p. 777. 



Stems round, simple or nearly so. Lower leaves alteniate, sub- 

 merged, very shortly stalked, oblanceolate or oval, on rather long stalks 

 and abruptly attenuated into the petiole ; upper leaves opposite, 

 rising out of the water, oval or ovate-oval or roundish-oval, frequently 

 subcordate at the base; all pellucid and membranous, with numerous 

 longitudinal ribs connected by transverse veins, which are very con- 

 spicuous if the dried leaf be held against the light, when the rather 

 minute areolation is clearly perceptible all over the leaf between the 

 ribs. Stipules large, blunt, not winged on the back, scarious. Peduncles 

 axillary, slender, not enlarged towards the apex. Sepals with their 

 lamina roundish-rhombic. Fruiting-spike cylindrical, many-flowered, 

 dense. Fruit green, very small, semicircular-ovoid, compressed, nearly 

 straight on the upper margin, semicircular and faintly keeled on the 

 back, with a short beak forming a continuation of the upper margin. 

 Young leaves bright grass-green, older ones olive. 



In shallow pools and ditches. Local, but widely distributed, 

 especially in fenny districts. In Scotland I have only found it in 

 Guillon Ponds, Haddingtonshire ; but it occurs also near Berwick, and 

 at Oban in Argyleshire. Rather rare, but generally distributed in 

 Ireland. 



England, Scotland, Ireland. Perennial. Summer, Autumn. 



Very similar in habit to P. polygonifolius ; but the lower leaves are 

 less distinctly stalked, and the upper ones have the lamina gradually 

 or suddenly contracted into the petiole, which is slightly enlarged 



