236 TETRANDRIA— TETRAGYNIA. Potamogeton. 



P. gramineum tenuifolium. Loes. Pruss. 206. t. 67. 

 Narrow Grass Pond-weed. Petiv. H.Brit, t.b.f. 11. 



In ponds and ditches, especially on a clay soil, not uncommon. 



Perennial. July. 



Much smaller than any of the foregoing. Stem slender, round, 

 more or less branched, from 1 to 2 feet long, altogether sub- 

 mersed, the flowers only appearing above-water. Leaves 1^ or 

 2 inches long, scarcely a line in breadth, opposite under every 

 flower-stalk, otherwise alternate, rather acute ; their mid-rib 

 slightly accompanied by oblong reticulations ; lateral ribs to- 

 wards the margins, solitary, very slender, and often hardly visi- 

 ble ; if continued far enough, joining the mid-rib, at some di- 

 stance below the point, and not quite both together. Stipulas 

 sheathing, broader than the leaves. Flower-stalks lateral, axil- 

 lary; the uppermost sometimes surmounted by a pair of branches; 

 all much longer than the small, ovate spike, which consists of 

 but hw Jlowers, becoming a little distant as the fruit advances. 

 Seeds ovate, obliquely beaked. 



A perfectly clear and well-known species, though Willdenow has 

 misquoted Haller, and Haller the Fl. Dan. A variety somewhat 

 larger than common, but not otherwise different, was found by 

 Mr. Teesdale, near Beverley, which I have from Switzerland for 

 compressum, and it is also marked Haller's 7i. 851 ; a combina- 

 tion of errors, for which the accurate Mr. Davall is not respon- 

 sible, for he had studied this genus correctly. 



13. P. pectinatum. Fennel-leaved Pond-weed. 



Leaves bristle-sliapetl, single-ribbed, parallel, thickly set in 

 two ranks ; sheathing at the base. Spikes interrupted. 



P. pectinatum. Linn. Sp. PL 183. Willd.v.l.7\5. Fl.Br.l97. 



Engl. Bot. V. 5. t. 323. Hook. Scot. 59. Ehrh. Herb. 123. 

 P. marinum. Linn. Sp. PL 184. Willd. v.1.716. Huds.76. FL 



Dan. t.\86. 

 P. n. 853. HalL HisL v. 1. 377. 



P. millefolium, seu foliis gramineis, ramosum. Raii Syn. 150. 

 P. maritimum, grandiusculis capitulis, capillaceo folio, nostras. 



Pluk. Almag. 305. L 216./. 5. DHL in Raii Syn. 150. 

 P. pusillum fluitans. Bocc. Sic. 42. t. 20. f. 5. 

 P. ramosum foliis gramineis. FailL Par. ]64. t. 32. f. 5. 

 Millefolium tenuifolium. Ger. Em. 828. f. 



In rivers, ditches and ponds, whether of fresh or salt water. 



Perennial. July. 



Root tuberous, with creeping scyons. Stems very much branched, 

 various in length, leafy, zigzag. Leaves alternate, two-ranked, 

 slender, tapering, acute, their solitary rib connected by trans- 

 verse alternate veins with the margins ; clasjjing the stem with 

 their elongated sheathing base, which appears to be lined with 



