230 TETRANDRIA— TETRAGYNIA. Potamogcton. 



Germ, for 1800. 81. Fl. Br. 1390. Engl. Bot. v. 18. t. 1285. 

 Hook. Scot. 57. IIoplc. Glott.27. Fl. Dun. t. 12G3. 



P. palustre. Teesdalt Tr. of Linn. S<><:. v. 5. 43. Relh. 64. 



P. gramineum. Light/. 123. FL Dan. i. 222; without the flouting 

 leaves. 



P. forte species, foliis tenuibus et pellucidis, lapathi minoris forma. 

 Dill, in Raii Syn. 150? 

 • P. folio angusto pellucido fere gramineo. Rati Syn. 148. ? 



P. n. 850. Hall. Hist. v. 1.377; excluding the reference to Ray. 



In pools and ditches. 



Near Beverley, Yorkshire. Mr. Teesdale. Berrington pool, Shrop- 

 shire. Rev. E. Williams. Cambridgeshire. Relh.&Rev.J.Hem- 

 sted. At Old Buckenham, Norfolk. Mr. D. Turner. In Bar- 

 dowie loch, Clydesdale. Hopkirk. Angusshire. Mr. G. Don. 



Perennial. July — September. 



Smaller than the last. Root a small tuber. Rev. J. Holme. Float- 

 ing leaves thinner, generally more pointed, scarcely heart-shaped, 

 seldom 2 inches long ; the submersed ones excessively nume- 

 rous, lanceolate, tapering at each end, not linear ; their length 

 1 j or 2 inches ; breadth at most half an inch ; with 3 or 5 prin- 

 cipal ribs. Stipulas blunter and shorter than the former. Flower- 

 stalks swelling upwards, or club-shaped, often crowded at the 

 tops of the branches. Spikes dense, about an inch long, the 

 stalks contracted suddenly below them. 



3. P. perfoliatum. Perfoliate Pond-weed. 



Leaves heart-shaped, clasping the stem, uniform, all sub- 

 mersed. 



P. perfoliatum. Linn. Sp. PI. 182. Willd. v. 1. 713. FL Br. 194. 

 Engl. Bot. v.3. t. 168. Hook. Scot. 58. FL Dan. t. 196. Rati 

 SynAW. Br. Prodr. 343. 



P. n. 845. Hall. Hist. v. 1.376. 



P. tertia. Dod. Pempt. 582. /. Ger. Em. 822. f. Bauh. Hist. v. 3. 

 770. f. 



P. rotunditolium alterum. Loes. Pruss. 205. t. 65. 



In ponds and rivers, very common. 



Perennial. July, August. 



Whole plant immersed in the water, except the spikes, which con- 

 sist of a few brown flowers, with copious white pollen. Their 

 stalks are rather tumid in the upper part. Leaves all sessile, 

 1 J or 2 inches long, uniform, olive-coloured, pellucid like oiled 

 paper, as Haller remarks ; harsh to the touch, but brittle ; their 

 ribs reddish. Seeds compressed, shining. Stipulas tight and 

 close. 



Haller esteems Loesel's plant a distinct species, and it is his own 

 n. 844. Dillenius has introduced it into Ray's Synopsis, next 

 to P. perfoliatum. The leaves are said by Haller to be firm (dura) 



