TEEES, SHEUBS, AND FOEESTS 



389 



The poplars, which are closely related to the willows, have a 

 similar natural habitat, but they grow to a greater size and are 

 of more value for timber or as ornamental trees than the willows. 

 The reproductive organs of willows and poplars are similar in 

 that the simple flowers of the poplars are borne in catkins, as in 

 the willows (Fig. 241). The individual flowers of the poplar, 

 however, differ in detail from those of the willow. The stamens 

 in the poplar are borne in considerable numbers on a bract with 



Leaf 



Catkin 

 '(female) 



Stem section 



Catkin, 

 (male} 



Male flower 



Fruit 



FIG. 241. Vegetative and reproductive parts of a poplar 



a hairy or roughened margin. The pistil resembles more nearly 

 that of the willow, but is characterized by a larger and much- 

 lobed stigmatic surface. Each pistillate flower is in the axil of 

 a bract like that which bears the stamens. The seeds in the cofc 

 tonwood (PopuluB deltoides) are well known for their cottony 

 covering of long, silky hairs. These hairs are outgrowths of 

 the seed coat, and when the fruit opens they expand and the 

 seeds can then be blown about by air currents. Pollination in 

 the poplars, unlike the willows, is effected by the wind (that is, 

 they are anemophilous), and the pollen, as in all wind-pollinated 

 plants, is produced in great profusion by the conspicuous pendent 

 male catkins, from which the pollen is easily scattered. 



