384 95. POTASfOGEIONACE^. 



ovate bluntly keeled. — P. compressus Sm. J3. B. 418. R. vii. 24, 

 not Fries, nor Koch. — Lateral veins nearer together and nearer 

 to the margin of the 1. than to the midrib (rarely some 1. are S- 

 veined), no intermediate veins. — Like Sp. 17 rather than Sp. 19. 

 —Ditches. P. VI. VII. E. S. L 



21. P. pusil'lus (1j.); st. subterete, I. linear 3-veined, spikes 

 short rather lax ^ or f shorter than the slender ped., sep. 

 rouudish-reniform, fr. obliquely ovate bluntly keeled. — F. B. 

 215. R. vii. 22. — St. slender. L. narrovr, rather acute, without 

 intermediate parallel veins, the lateral veins equidistant between 

 the midrib and margin. Ped. scarcely compressed, not thickened. 

 — [P. rutilus (Wolfg., Fries) has 3-veined attenuate-cuspidate 

 1., semiterete st., and oblong-elliptio fr. without a keel. Fl. Ban. 

 2891.]— Ponds and ditches. P. VI. E. S. I. 



22. P. trichoides (Cham.) ; st. subterete, I. siibaetaoeous 1- 

 veined finely pointed, spikes short lax long-stalked, fr. semicir- 

 cular compressed obscurely keeled, st.raight inner edge with « 

 tooth near its base. — Sy. E. B. 1420. R. vii. 21. — St. very 

 slender, a little thickened below the joinings ; branches fascicu- 

 late. L. not transversely veined. Jloral stip.large. Ped. not 

 thickened. Sep. roundish, stalked. Monandrous. Fr. often 

 warted on the back and with a tubercle on each side at its base 

 when fresh. — Pramlingham, Norf. Wrotham, Suif. P. VII. 

 VIII. E. 



**l* L. all svbmersed, alternate, linear, sheathing. 



23. P. flabelldtus (Bab.) ; lower I. broadly linear abruptly 

 apiculate or acuminate 3 — 5-veined with transverse veins, tipper 

 I. narrow acute 3-veined, fr. (2 lin. long) broadly J-obovate 

 inner edge nearly straight but gibbous near the top rounded on 

 theback, nut with a prominent keel. — Sy. E.B. 1421. Phytol.'w. 

 1158. — Rhizome spreading, from a tuber that has outlived the 

 winter. Floating st. branched, spreading like a fan. Broad 

 lower 1. usually decayed at the time of flowering. Lateral veins 

 of upper 1. at the margin, of lower 1. distant from it. Spikes 

 slightly interrupted. Back of fr. without ridges, rounded when 

 fresh ; enclosed nut with faint lateral ridges. — Ponds and ditches 

 chiefly near the sea. B. VI. VII. E. I. 



24. P. pectindtus (L.) ; I. formed of 2 interrupted tubes, lower 

 narrowly linear flattened slightly grooved above, upper setaceous, 

 fr. (2 lin. long) bi'oadly -^-obovate inner edge rather convex 

 rounded on the back, nut with 2 lateral ridges but (usually) no 

 heel. — E. B. 323. R. vii. 19. — St. branched, forming linear 

 masses. L. very gradually acute, all 1-veined, no marginal veins 

 and scarcely thickened there ; upper 1. with an oval section. 



