256 



PLANT STRUCTURES 



temperate regions, for here belong the oak (Fig. 238), hick- 

 ory, walnut, chestnut, beech, poplar, birch, elm (Figs. 198, 

 239), willow (Fig. 240), etc. The primitive character is in- 

 dicated not merely by the floral structures, but also by the 

 general anemophilous habit. 



In the poplar (Populus) and its allied form, the willow 

 (Salix), the flowers are naked and hypogynous (Fig. 196), 



FIG. 239. An elm in foliage. From "Plant Relations. 1 ' 



