5l6 NAIADACE/K 



10. P. ititeiis (Gli.steniiig Pond-weed). — A closely allied, much 

 branched form, with numerous rooting- branches springing from 

 the axils of its upper leaves ; leaves' usually all submerged, 

 scattered, recurved, with a wavy margin and a shining surface ; 

 flowers in shorter spikes, thickening less upward. — Ditches ; chiefly 

 rn the north ; uncommon. — Fl. June — September. Perennial. 



I r. P. liuens (Shining Pond-weed). — The largest iiritish species ; 

 stem stout, 3 — 6 feet long; leaves mostly submerged, shortly- 

 stalked, 4 — 10 in. long, oblong-lanceolate, wavy, toothed, pellucid, 

 many nerved ; stipules large, long, ket^led ; flowers in a stout, 

 dense, cylindric spike on a short, thick stalk, thickcmng upward ; 

 carpels small, rounded, vv'ith a short, blunt beak. — Lakes ; frequent. 

 — Fl. June — September. Perennial. 



12. P. declpiens. — A closely allied form with sessile, broad, 

 pointed, scarcely toothed leaves; short, scarcely vi'mged stipules ; 

 and shorter fluwer-stalks. 



13. P. aiigustifolhis. An allied, but smaller, much branched 

 species ; leaves long-stalked, with entire margins, upper floating, 

 obovale-oblong, wedge-shaped at the btiSe, rather leathery, lower 

 often recurved ; flower-spikes i — 2 m., on very long stalks ; 

 carpels rounded. — Ponds ; not commofi. — Y\. June — September. 

 Perennial. 



t4. P. Grifl'ithu. a rare form, with branched stem; leaves all 

 submerged, 7 — 12 in. long, 11 — 17-nerved, narrow, boat-shaped 

 at the ape.x ; stipules long, narrow, and blunt ; flowers in dense 

 spikes on slender stalks shorter than the leaves ; occurs only in 

 Aber Lake, Carnarvonshire. — Fl. June, July. Perennial. 



_ 15. P. prcelimgus (Long-stalked Pond-weed). — A similar species 

 with stout, greenish-white stem ; leaves linear-oblong, blunt, 

 entire, half-sheathing, concave at the tip,. 3-nerved ; stipules large, 

 blunt ; flowers in dense cylindric spikes ori very long, stout stalks ; 

 carpels large, with sharp keels.— Lakes and deep rivers ; local. — 

 Fl. May — July. Perennial. 



^ 16. P. perjulidtus (Perfoliate Pond-wfced). — Stem round, stout, 

 dichotomously branched; leaves s.\\ subhiersed, egg-shaped 2 — 3 

 in. long, embracing the stem, pellucid, 5 — 9-nerved, brown, and 

 almost transparent, having when dry the appearance of gold- 

 beaters' skin, and so sensitive to moistui"e that they will curl when 

 laid on the palm of the hand; stipules small, follmg off; flowers 

 in dense spikes on short, stout stalks ;' carpels scarcely keeled, 

 with short beaks.— Ponds and lakes ; common.— Fl. June- 

 September. Perennial. 



17. P. crlspus (Curly Pond- weed). —5/f»; slender, compressed, 

 dicholomously branched ; leaves alternate, close-set, i — 3 in. lon^, 



