100 



THE WALNUT FAMILY JUGLANDACEAE. 



This family comprises about 6 genera with 35 species of trees and 

 shrubs found chiefly in the warmer portion of the north temperate 

 zone. Two genera with about 19 species are native to North Amer- 

 ica. Both of these genera, Juglans and Carya, have representatives 

 in Pennsylvania. The former genus has 2 species and the latter 5 

 species native to the State. In addition to the existing species a 

 great number of fossil species have been referred to this family. 

 Thirty fossil species belonging to the genus Juglans .and 10 species 

 belonging to the genus Carya have been described. 



This is one of the most important families of trees native to Penn- 

 sylvania. Both the Hickories and the Walnuts yield very valuable 

 wood. The wood of the Walnuts is esteemed especially for cabinet 

 work and that of the Hickories on account of its strength and flexi- 

 bility. The bark and husks of the Walnuts are used sometimes as a 

 dyestuff. The fruit of both genera is edible. 



The staminate and pistillate flowers are separate but borne on 

 the same tree and usually in the same branch. The staminate flow- 

 ers are in long drooping aments while the pistillate appear as buds 

 and occur in small few-flowered clusters. The leaves of both genera 

 are compound and alternate. The fruit is a nut. The nut of the 

 Walnuts is sculptured and covered with a fleshy, indehiscent, pulpy 

 husk while the nut of the Hickories is not sculptured but covered 

 with a dehiscent husk. 



KEY TO THE GENERA. 



Page. 

 1. Pith of twigs chambered; nuts sculptured or rugose with indehiscent husk; staminate 



catkins thick, compact, usually sessile and solitary; wood diffuse-porous Juglans 101 



1. Pith of twigs continuous; nuts smooth or ridged with dehiscent husk; staminate 



catkins slender, loose, long-stalked, in 3s; wood ring-porous, Carya lOi 



