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 j the uppermost sometimes surmounted by a pair of branches j 

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

 but few 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 n. 851 ; a combina-r 

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

 siblCj for he had studied this genus correctly. 



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



' Leaves bristle-shaped, single-ribbed, parallel, thickly set in 

 two ranks ; sheathing at the base. Spikes interrupted. 



P. pectinatum. Linn. Sp. Pl.lS^. Willd. v. I. 715. Fl. Br. 197, 

 Engl. Bot. v.b. t. 323. Hook. Scot. 59. Ehrh. Herb. 123. 



P. marinum. Linn. Sp. PL IS4. Wiild. v.1.7 \6. Huds.76, FL 

 Dan, t. 18(3. 



P. n. 853. Hall. Hist. v.\. 377. 



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



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

 Pink. Almag. 305. ^. 2 1 6. /. 5 . Dill, in Rail Syn. 150. 



P. pusillum fiuitans. Bocc. Sic. 42. t. 20. f. 5, 



P. ramosum foliis gramineis. Vaill. Par. 164. t.32.f. 5. 



Millefolium tenuifolium. Ger. Em. 828./. 



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 ; clasping the stem with 

 their elongated sheathing base, which aj)pears to be lined with 



