TETRANDRIA— TETRAGYNIA. Potamoceton. 229 



»■ 



tuse, permanent. Seeds 4, naked, roundish ; tumid at the 

 back ; compressed or angular at the inner margin. " Em~ 

 bryo curved," almost double. Gartn. Br. 

 Aquatic, floating or immersed, herbs, of a highly vascular 

 texture, whose evaporation, by their whole surface, is ex- 

 tremely copious and rapid. Stem branched. Leaves alter- 

 nate, or opposite, stalked or sessile, simple, undivided, * 

 entire, rather membranous, smooth, with parallel longitu- 

 dinal ribs. Flowers spiked, greenish, raised above the 

 water ; the seeds ripened at the bottom. Four of our 

 species are found in New Holland. 



1. P. natans. Broad-leaved Pond-weed. 



Upper leaves oblong-ovate, stalked, floating, coriaceous; 

 lower ones linear, membranous, sessile. 



P. natans. Linn. Sp. PL 182. Willd.v. 1 . 712. Fl. Br. 193. Engl. 

 Bot.v. 26. t. 1822. Hook. Scot. 57. Mill, lllustr. t.W. FL Dan. 

 t. 1025. Br. Prodr. 343. 



P. n. 843. Hall. Hist. v.]. 375. 



P. rotundifolium. Raii Syn. 148. Bauh. Pin. 193. 



P. latifolium. Ger. Em. 821./. 



Potamogeton. Matih. Valgr. v. 2. 481./. Camer. Epit. 873./. 

 Fuchs. Hist. 65 1 ./. Trag. Hist. 688./ 



In pools, ditches, and slow rivers. 



Perennial. July. 



Roots creeping extensively in the mud. Stem round, much branch- 

 ed, several feet in length. Lowermost leaves alternate, linear, 

 acute, very narrow, sessile, membranous ; uppermost floating, 

 partly opposite, leathery, smooth, deep green, 2 or 3 inches long, 

 elliptical, often heart-shaped, with about 7 main ribs, and some 

 intermediate ones ; involute in the bud. Footstalks various in 

 length, semicylindrical, very vascular. Stipulas intrafoliaceous, 

 large, lanceolate, acute, concave, pale and membranous. Spikes 

 simple, raised an inch or two above the water, each on a long, 

 thick, axillary stalk, suddenly contracted at the bottom of the 

 spike. FL a little distant, quite sessile, rather numerous, ver- 

 tical, olive green, with yellow anthers, and plenty of whitish 

 pollen. 



Except as manure, I know of no use for this, or any of the genus. 



2. P. heterophyllum. Various-leaved Pond- weed. 



Upper leaves elliptical, stalked, floating, slightly coriaceous; 



lower ones lanceolate, membranous, sessile. Flower-stalks 



swelling upward. 

 P. heterophyllum. Schreb, Lips.2\. WilhlSp. PLv. 1.713. Hoffm. 



