354 94. POTAMOGETONACE^. 



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

 cular compressed obscurely keeled, straight inner edge with a 

 tooth near its base. R. vii. 21. St. very slender, a little 

 thickened below the joinings. L. not transversely veined. 

 Floral stip. large. Ped. not thickened. Sep. roundish, stalked. 

 Fr. often verrucose on the back and with a tubercle on each side 

 at its base when fresh. About Norwich. P. VII. VIII. E. 



**** L, all submersed, alternate, linear, sheathing. 



18. P. flabellatus (Bab.) ; lower I. broadly linear abruptly 

 apiculate or acuminate 3 5-veined with transverse veins, float- 

 ing 1. narrow acute 3-veined, fr. (2 lin. long) broadly ^-obovate 

 inner edge nearly straight but gibbous near the top rounded on 

 the back, nut with a prominent keel. Phytol. iv. 1158. P. zos- 

 teraceus Bab. (not Fr.}. 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 ; inclosed nut with faint lateral ridges. 

 Ponds and ditches. P. VI. VII. E. 



19. P. pectinatus (L.) ; I. formed of 2 interrupted tubes, lower 

 narrowly linear flattened slightly grooved above, upper setaceous, 

 fr. (2 lin. long) broadly i-obovate inner edge curved back rounded 

 on the back, nut with 2 lateral ridges but (usually) no keel. 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. Spikes slightly 

 interrupted. Back of fr. without ridges and rounded when 

 fresh ; nut with strong lateral ridges. Varying greatly in 

 length and size of st. and leaves. Ponds and streams. P. VI. 

 VII. 



20. P. Jiliformis (Nolte !) ; I. linear-setaceous 1 -veined with 

 transverse veins, spikes greatly interrupted, fr. (H lin.) obovate 

 rugose rounded on the back without keel or ridges when dry, nut 

 round-backed. L. like those of the preceding but longer. Fr. 

 smaller. Whorls very distant on the spikes. Peduncles very 

 long. Rare. Forfarshire and Berwickshire. P. VI. VII. S. 



***** L. all opposite, submersed j stipules none. 



21. P. densus (L.) ; L all opposite pellucid clasping elliptical- 

 lanceolate or lanceolate, spikes shortly stalked ultimately reflexed. 

 E. B. 397. R. vii. t. 28. L. crowded, rather recurved. Spike 

 4-flowered. Sep. triangular. Ditches. P. VI. VII. 



