KEY TO GENERA AND SPECIES 53 



97. Mature leaves silky hairy on both surfaces. 

 Twigs greenish. Cult, and escaped. Native 

 in Europe. (Fig. 90.) White Willow, Salix 

 alba L. 



97. Mature leaves smooth. Twigs yellow or red- 

 dish. Cult, and escaped. (Fig. 91.) Yellow 

 Willow, Salix alba var. mtettina (L.) Koch. 



97. Mature leaves smooth and bluish green. Twigs 

 olive-green. Cult, and escaped. (Fig. 92.) 

 Blue Willow, Salix alba var. caerulea (Sm.) 

 Koch. 



POPLAR. Leaves wide.* Flowers in catkins. Sta- 

 mens 8 or more. Bracts fringed. Fruit 

 essentially as in Willow. 



98. Leaf margins irregularly lobed 

 or toothed; lower surface 

 white-cottony even when old. 

 Cult, and escaped. Very va- 

 riable. Native in Eurasia. 

 (Figs. 93, 94.) White Poplar, 

 Abele, Silver Poplar, Populus ..., 



White Poplar. 



alba L. 



98. Leaf margins regularly (or but slightly irregu- 



larly) toothed 99. 



99. Teeth 5 or less per inch of margin. Through- 



* Sometimes narrow in the American Aspen. 



