PART II 



KEY TO THE ECONOMIC WOODS OF THE 

 UNITED STATES 



I. Homogeneous or Non-porous Woods: Gymnosperms; 

 Conifers; "Soft Woods" 



Vessels absent; wood composed mostly of tracheids miiform in 

 structure and arranged in definite radial rows. Growth rings 

 defined by the greater density of the late wood. Resin cells and 

 resin ducts present or absent. Rays very fine, numerous, incon- 

 spicuous. 



A Resin ducts, both vertical and horizontal, present. Rays with 

 ' tracheids. 



1 With clear demarca tion in color between heartwood and 

 sapwood. 



a Resin du cts plainly visible to the unaided eye, numernus. 

 often well distributed; tyloses present; epithelium thin- 

 walled.. Resin cells absent. Wood with characteristic but 

 not always pronounced resinous odor . Pine.' 



a' Little contrast between early and late wo od. Wood soft 

 to medium; only moderately resinous; texture uniform; 

 color light or reddish, variable! Upper and lower walls 

 of the few and small ray tracheids smooth (Figs. 4-5). 

 Pits present on the tangential walls of the tracheids of 

 the late wood. Soft Pine Group. 



NoTir. — The letters in parentheses following the specific names refer to 

 the map (Plate I, Natural Forest Regions of the United States), and in- 

 dicate in a general way the distribution of the species. 



(P), Pacific Coast Forest; (R), Rocky Mountain Forest; (N), Northern 

 Forest, general; (L), Lake States Forest; (A), Appalachian Forest; (C), 

 Central Hardwood Forest; (S), Southern Forest; (T), Tropical or Sub- 

 tropical Forest; (n), north; ■ (s), south. Where more than one region is 

 indicated, the more important is placed first. 



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