POTAMOGETOX. 443 



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

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

 thickened. Sep. roundish, stalked. Fr. often waited on the 

 back and with a tubercle on each side at its base when fresh. 

 Norf. Suff. Camb. Devon. Surrey. P. VII. VIII. E. 



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



28. P. Jlabelldtus (Bab.) ; lower I. broadly linear abruptly 

 apiculate or acuminate 3 ^-veined with transverse veins, upper 

 I. narrow acute $- 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. Sy. E. B. 1421. PhytoL iv. 

 1158. Bhizome spreading, from a tubar that has outlived the 

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

 Broad 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. [A slender maritime 

 form with setaceous 1. is var. scoparius (Fryer).] Ponds and ditches 

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



29. P. pectindtus (L.) ; /. formed of 2 interrupted tubes, lower 

 narrowly linear flattened slightly grooved above, upper setaceous, 

 fr. (2 lin. long) broadly j-obovate inner edge rather convex 

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

 keel. E. B. 323. 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. P. manVzws (Huds.) 

 has the stems naked below. Sy. E. B. 1423. Ponds and 

 streams. P. VI. VII. E. S. I. 



30. P. filifor'mis (Pers.) ; I. linear-setaceous 1-veined with 

 transverse veins, spikes greatly interrupted, fr. (1^ lin.) obovate 

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

 round-backed. Sy. E. B. 1424. L. like those of the preceding 

 but longer. Fr. smaller. Whorls very distant on the spikes. 

 Peduncles very long. Lakes, rare. P. VI. VII. E. S, I. 



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



31. P. den'sus (L.) ; L all opposite pellucid clasping elliptic- 

 lanceolate or lanceolate, spikes shortly stalked ultimately re- 

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

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



E. S. I. 



