HISTOEY OF THE WILLOWS AND POPLARS 23 



willow (Salix alba) and the crack willow {Salix Jragilis) both 

 occur in France and Wiirtternberg. With the amelioration of 

 conditions following the last retreat of the ice the Arctic forms 

 withdrew to the far north with the sub-arctic and cool temperate 

 species in their wake, and these far northern forms are circuni- 

 polar at the present time, although those willows that, attain to 

 the stature of trees and inhabit the Temperate Zone are different 

 in each of the three continents of the Northern Hemisphere. 



The poplars, while they show their community of origin with 

 the willows, differ from them sufficiently to be readily distin- 

 guishable. They are all" trees and on the whole average larger 

 than the willows. The catkins are pendulous instead of erect; 

 there is a rudimentary perianth or flower envelope, and the 

 bracts of the flowers are toothed or cleft instead of entire as in 

 the willows ; the leaves are usually broad instead of narrow being 

 ovate or deltoid and often cordate, and the leaf-stalks are long 

 and often flattened — a feature well exemplified in the quaking 

 aspen. 



The generic name Populus is of obscure etymology but was the 

 classical name of the poplar, of which there are several European 

 species. The most important of these is the white, silver poplar 

 or abele (Populus alba), a large tree of the central and southern 

 parts of that continent. The black poplar is also a large tree 

 of central and southern Europe and Asia. An aspen {Populus 

 tremula) occurs in central and northern Europe ranging east- 

 ward to Japan, and there are a number of additional European 

 species, including the downy poplar {Populus canescens) ; Populus 

 monilifera, which furnished the poplar wood of the Romans; 

 and the so-called Lombardy poplar {Populus fastigiata) so 

 often planted in this country as a screen or ornamental tree. 

 The last is probably of oriental origin despite its name, coming 

 originally from the region of the Vale of Kashmir, since it seems 

 to have been unknown in Italy in Pliny's time. Populus 

 euphratica of North Africa, the Altai and Hunalayan region 

 is believed to have been the weeping willow of the Scriptures and 

 its wood along with that of the date palm furnished the rafters 

 for the buildings of Nineveh. The bud gum of the European 



