POTAMOGETONACEJl. 293 



First record : Varenne, 1827. The least abundant in its localities, usually 

 occurring sparingly along with L. minor. 



WOLFFIA, Horkel. 



709. 'W. arrbiza, Wimm. Lemna arrhiza, L. (Bab. Man. and Syme 

 E. B.). 

 Syme E. B. ix. t. 1398 (not at all characteristic). 

 Floating on clear water ; very rare. P. Flowers not yet detected in 



England. 

 II. Piece of water which probably communicates with the Thames, but 

 looks like a pond, near the railway bridge on Staines Common, June 

 14, 1866. Still abundant there in 1868, but it has not spread into 

 the other ponds near. 

 First record: Trimen, 1866; also first as a British plant.* Probably 

 occurs in other localities; but overlooked from its minuteness. Since 

 its discovery in Middlesex, it has been found at Walthamstow, Essex, 

 by Mr. Moggridge ; near Canterbury, Kent, by Mr. Gulliver ; and in 

 several spots in Surrey by Mr. Watson and Eev. W. W. Spicer. 

 Wolffia is undoubtedly a good genus. (See Dr. Hegelmaier's monograph, 

 Die Lemnaceen (1868), where twelve species are described.) 



POTAMOGETONACE^. 



POTAMOGETON, Linn. 

 710. P. natans, L. 



P. majus vulgare, Matth. (Johns.). P. latifolium, Ger. em. (Pet., 



Blackst.). 

 Cyb. Br. iii. 201. Syme E. B. ix. t. 1399. 

 Ponds and ditches ; common. P. June — August. 

 I. Harefield ! ; Blackst. Fasc. 80. Uxbridge ! ; Newb. Elstree Eeservoir. 

 Near South Mims. 



III. Near Hatton. 



IV. Harrow district, abundant; Melv. 83. Hampstead Heath; Johns. 



Enum. and Irv. MSS. Harrow Weald. 

 V. Brent, near Ealing ; Herb. Devon Institution, Exeter. NearWiLLesden 

 Junction ! ; Warren. Peri vale ; Lees. 

 VI. Near Whetstone. Ditch near Pickard's Lock, Edmonton, 



» In Seem. J. of Bot. iv. (1S66) p. 263, is a communication from Dr. J. E. Gray, stating 

 that ' about fifty yeai-s ago,' some specimens were seen by him and Mr. J. J. Bennett, said to 

 have been ' discovered in the neighbourhood of Loudon,' by M. Gerard. They were at the 

 time considered to be ' a very young state of Lemna minor,' and as no specimens were pre- 

 served, the truth of tUs supposition can be now neither supported nor disproved. There- 

 fore, it ia not possible to admit that the occurrence of the species in England was a knoicn 

 fact at that somewhat distant period, although there is no reason to suppose the plant a 

 recent importation into this country. 



