CLASS ir. ORDER m. J POTAMOSETON, 213 



than the rest; flower- stalk not thickened upwards."— H^eVsow, in 

 Hooker's British Flora. 



Habitat. — Ditches and slow streams; not nnfrequent. Beverley, 

 Yorkshire; in the Gaddie Preranay, Aberdeenshire; Anglesea; near 

 Glasgow, and Forfar ; Lilleshall Mill-pond, Shropshire. 



Perennial ; flowering in July and August. 



14. P. oblon'gns, Viv. (Fig. 279.) hlunt- fruited broad-leaved Pond- 

 weed. Leaves floating, coriaceous; lower ones sometimes sub- 

 mersed, without leafless petioles. 



Hooker, British Flora, vol. i. p. 78.— Lindley, Synopsis, p. 250. 

 Floating leaves more or less coriaceous, submersed ones often absent. 

 Fruit rounded, and obtuse at the back. 



Habitat. — Ditches near Henfield — Mr. D. Turner. 

 Perennial ; flowering in July. 



15. P. na'tans, Linn. (Fig. 280.) sharp-fruited broad-leaved Pond- 

 weed. Submersed leaves linear, membranaceous, not always pre- 

 sent ; floating ones elliptical, stalked, coriaceous, and many-nerved. 



English Botany, t. 1822.— English Flora, vol. i. p. 229.— Lindley, 

 Synopsis, p. 250, — Hooker, British Flora, vol. i. p. 78. 



Roots creeping. Stem round, several feet in length, much branched. 

 Upper leaves two or three inches long, elliptical or heart-shaped, on 

 long footstalks, nearly opposite, with five or more main ribs springing 

 from the centre one ; lower ones often wanting in shallow water, nar- 

 row, sessile, alternate. " The lower leaves appear to me to differ from 

 the submersed leaves of all the others (except the last perhaps) in 

 having their substance composed of the same small but distinct cells, 

 or reticulations, as the floating ones." (Hooker.) Stipules lanceolate, 

 large, and foliaceous. Peduncle long, thickened upwards. Spike 

 dense, cylindrical, rising several inches above the water. 



Habitat. — Ditches and stagnant pools ; common. 



Perennial ; flowering in June and July. 



It is at all times a matter of much greater difficulty to cultivate 

 aiiuatic plants successfuly, than such as only require a suitable soil, 

 and free exposure to the common atmosphere of our climate. The 

 aquatic may be indiff"erent to the particular kind of earth to which its 

 roots are exposed, provided the watery element in which it is immersed 

 be adapted to its habit and nature ; but to insure success in its culture, 

 it is not enough that the plant be placed in water, with its roots sur- 

 rounded with earth, nor does it require extended observation to prove, 

 that it is an important fact, in their natural habitation, that while one 

 is detected revelling in all the luxuriance of growth, amid volumes of 

 pernicious gasses hourly poured forth from some stagnant pool, anothe 

 may be sought in vain, except in some 



