LEADING FAMILIES OF FLO WEEING PLANTS 351 



(Fig. 285), often one or both kinds in catkins. In the Elm 

 family (Fig. 286) the flowers are usually bisexual. A fifth 

 family, that of the mulberries, includes among the economic 

 plants of temperate North America few except the mulberries 

 and the Osage orange, the hemp and the hop. This family also 

 embraces the tropical breadfruits, and the great fig genus of 



FIG. 285. Gray birch (Betula populifolia) 



A, catkins, natural size: s, staminate; p, pistillate. B, cluster of ripened fruits; 



C, bract with three staminate flowers ; D, bract with three pistillate flowers ; E, 



fruit. B, C, D, E, somewhat magnified 



some 600 species, including the edible fig and the rubber tree 

 (Ficus elastica). 



Edible seeds of many kinds are produced by members of the 

 families of catkin-bearing trees. Most familiar are the Ameri- 

 can and the European walnuts, the hickory nut, and the pecan. 

 Hardly less so are the American and the European chestnuts. 



Edible fruits not however of much importance are borne 

 by the mulberries. The breadfruit, from a tree of the same 



