294 POTAMOGETONACEJ;. 



Vn. Ponds about London ; Herh. Pet, Isle of Dogs, 1817 ; Herb. G. ^- E. 

 Lea Canal ; Cherry {v. «.). 

 First record: Petiver, ahont 1710, 



711.> Pi polygronlfolius, Pourr. 

 P. ohlongus, Viv. (Melvill). 

 Cyb. Br. iii. 21. Syme E. B. ix. t. 1400. 

 Ponds and ditches, on heaths ; very rare. P. June — September. 



I. Ditch at Harrow Weald Common ! ; Melv. 83. 

 IV. North Heath, Hampstead. 



First record : Hind, 1861. The plant at Harrow Weald Common grows 

 in rather deep water, and is quite like the figure quoted. That at 

 Hampstead is the usual heath form (7 erioetorum, Syme). 



(P. fluitans. Both. A plant which may be this is in Lamb. Herb, at Kew ; 

 it was gathered at Hounslow ; Bab. Man. 362. An error (see Syme 

 E. B. ix. 63).) 



P. rufescens, Schrad. Cyb. Br. iii. 20. Syme E. B. is. t. 1402. Should 

 be looked for.* It occurs in ditches by the Colne, bet. Rickmansworth 

 and Harefield Mill; Fl. Herts. 274, a station which if not within must 

 be very slightly beyond our boundaries. 



712. P. lucens, L. 



P. aquis immersum fol. jpellucido lato oblongo acuto (Budd., Pet.). 



Cyb. Br. iii. 16. Syme E. B. ix. t. 1408. 



Eivers and streams ; rather rare. P. Jime — August. 



II. Thames above Teddington Lock. 



III. On Hounslow Heath ; Budd. MSS. vi. Chase Bridge, Whitton, G. 



Francis ; Coop. Supp. 12. Duke's Eiver, near Isleworth. Thames, 



Twickenham. 

 V. Canal near Brentford ; Hemsley. 

 VII. Many places in Thames bet. Fulham and Hampton Court ; Pet, Midd. 



[Ditches near Chelsea Waterworks, M. df G, 206.] Lea Navigation ! 



and Hackney Canals !, abimdant ; Cherry. 



Var. p. P. acuminatus, Schum. 

 VII. Floating in the Hackney Canal. 



First record: Petiver, 1695. [P.fol. angusi. pellucid, fere gramineo, vel 

 Hit simillimum, at Jack Straw's Castle ; Boody MSS. and R. Syn, iii. 

 148, is perhaps a form of this.] 



713. P. perfoliatus, L. 



Cyb. Br. iii. 15. Syme E. B. ix. t. 1412. 



Streams and ponds ; rather common. P. June — August. 



* The species of Potarm>geU>n, together with many other water plants, have become 

 much less frequent, and are threatened with extinction in consequence of the extraordinary 



increase of Elodea, 



