44 TETRAXDRIA TETRAGYXIA. Potamogeton. 



bractea like the stip.) thick, ahnost cyhndric, contracted just 

 under the spike. Fl. dull-green, pollen whitish. Spike raised 

 above the water. Ls. foot-stalks long. 

 Floating Ls. a shade to fish : roots favourite food of swans. 



P. perfoliatus. Perfoliate P. Leaves heart-egg- 

 shaped, clasphig the stem, uniform, all beneath the 

 water ; spikes of flowers above water. E. B. 168. 

 G. E. 822. 



Ponds, rivers. 



Per. June. 



Stems long, round. Ls. pellucid, olive-coloured, crowded about the 



top, and branches. Spikes a few brown ^. 



The respiration of these submersed plants probably different 

 from that of plants, which inhale atmospheric air : the Is. of a tliin, 

 pellucid texture, very vascular ; the surface destitute of hair, or 

 down. 



P. deiisus. Close-leaved P. Leaves egg-shaped, stalk- 

 less, pointed, opposite, crowded. Stem forked. Spike 

 of about four flowers. E. B. 397' 



Ditches, ponds, slow streams. 



Per. July. 



Ls. lengthened into a point, ribbed waved, entire, much crowded 

 towards the end of the stem. Fl. stalks short, round, curved 

 back, bearing a small short head of two or four green fl. much 

 resembling those of Ado.ra Moschatellina. Plant immersed, ex- 

 cept the spike. Smaller than P. perfoliatus. 



P. lucens. Shining P. Leaves elliptic-spear-shaped, 

 pointed, membranous, stalked, repeatedly triple-ribbed, 

 all under water. Spike dense, many-flowered, above 

 water. E. B. 376. P. longis acutis foliis. G. E. 822. 



Ditches, ponds, lakes, slow streams. 



Per. July. 



Stems long, slightly zigzag, round, leafy. Ls. alternate, except 

 where fl., foot-stalk short : stip. long, blunt, folded, membrana- 

 ceous within the Ls. FL on a solitary spike ; the longest, and 

 most crowded of the genus ; from the axil of one of the opposite 

 Ls. dark-green ; plant olive-gi-een or reddish. L^ar. one with 

 spear-shaped, tapering Ls. 



P. crispiis. Curled P. Freshivater^ Caltrops. Leaves 

 spear-shaped, waved ; saw-toothed, alternate ; the 

 uppei" ones opposite. Flowers in loose spikes. E. 

 B. 1012. C. 5. 15. Tribulus aquaticus minor, quer- 

 cus floribus. G. E. 824. 



' Ang. Sax. 



