174 ALIEN FLORA OF BRITAIN 



Juglans regia, L. Native in woods from the Caucasus 

 to India. In recent geological times its range reached 

 and included England, but now it is only known as 

 a cultivated tree. 



Populus alba, L. Native of damp woods in Central 

 and Southern Europe. There seems to be a general 

 impression among botanists in England, Normandy^ 

 and Belgium that it is nowhere indigenous in those 

 countries. It is widely planted, and is common in 

 many parts of England along river banks and other 

 wet places. It would probably be difficult to prove- 

 its exotic origin, but until its situation in Northern 

 Europe has been carefully re-examined it should not 

 be admitted to our native list. 



Populus balsamifera, L. A native of the borders 

 of swamps and rivers in North America. It is rather 

 frequently planted in England, and it is occasionally 

 recorded from semi-wild situations. 



Populus monilifera, Ait. A native of the margins 

 of lakes and streams in North America. It is occasion- 

 ally planted in England, and rarely noticed as art 

 escape from cultivation. 



Populus nigra, L. Native of Central and Southern 

 Europe. A commonly planted Poplar in England,, 

 Belgium, and Normandy. As in the case of Populus alba^ 

 until its whole position in Northern Europe is carefully 

 considered it should be treated as an introduction. 



Populus pyramidalis, Salisb. A widely cultivated tree. 

 Not uncommon in England, but only as a planted tree. 



