5l6 NAlADACEiE 



10. P. nitens (Glistening 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 

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



11. P. lucens (Shining Pond-weed). — The largest British 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, keeled ; -flowers in a stout, 

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

 carpels small, rounded, vs^ith a short, blunt beak. — Lakes ; frequent. 

 — Fl. June — September. Perennial. 



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

 pointed, scarcely toothed leaves ; short, scarcely winged stipules ; 

 and shorter flower -stalks. 



13. P. angustifolius. — An allied, but smaller, much branched 

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

 obovate-oblong, wedge-shaped at the base, rather leathery, lower 

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

 carpels rounded. — Ponds ; not common. — Fl. June — September. 

 Perennial. 



14. P. Griffithii, a rare form, with branched stem ; leaves all 

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

 at the apex ; 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. prcBlongus (Long-stalked Pond-weed). — A similar species 

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

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

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

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

 Fl. May — July. Perennial. 



16. P. perjolidtus (Perfoliate Pond-weed). — Stem round, stout, 

 dichotomously branched; leaves slW submersed, 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 moisture that they will curl when 

 laid on the palm of the hand ; stipules small, falling 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. crispus (Curly Pond- weed). — Stem slender, compressed, 

 dichotomously branched ; leaves alternate, close-set, i — 3 in. long, 



