ECONOMIC "WOODS OF THE UNITED STATES 



colored portion, the heartwood, and a nearly colorless outer border, 

 the sapwood. In fresh-cut green sections the sapwood is further 

 differentiated by its greater moisture content. 



Indigenous arborescent plants are readily separable into two 





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Fig. 1. — Crosa section of stem of Querctis frimis (chestnut oak); h, bark 

 showing outer and inner portions; s. w., sapwood: the darker inner portion is 

 heartwood; «. /., annual or growth ring; p. r., (pith) ray, a large number of which 

 can be seen crossing the growth rings at right angles. Note season checks. Natural 

 size. (From Bui. 102, U. S. Forest Service.) 



great natural classes: I, Gymnosperms, and II, Angiosperms. 

 Plass I is further divided into two unequal groups: Coniferce (13 

 genera), and Taxacece (2 genera). Class II embraces (according to 



