PART II 



KEY TO THE ECONOMIC WOODS OF THE 

 UNITED STATES 



EXPLANATORY NOTES 



The descriptive key given in the following pages is based upon 

 features visible with the unaided eye and with a small hand lens, 

 and also upon features visible only under the compound micro- 

 scope. The latter are indicated by smaller type. 



The small numerals following the names of the woods refer to 

 a Ust of references on pp. 109-117. 



The capitals in parentheses following the specific names refer 

 to the regions indicated on the map (Plate I, Natural Forest 

 Regions of the United States) and indicate in a general way the 

 natural distribution of the species: 



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

 Northern Forest; (C), Central Hardwood Forest; (S), Southern 

 Forest; (T), Tropical or Sub-tropical Forest; (n), north; (s), south; 

 (Int.), Introduced into the United States. Where more than one 

 region is indicated the more important is placed first. 



I. Non-porous Woods: Gymnosperms, Conifers, Soft- 

 woods. (For II, see p. 85.) 



Vessels absent. Woods comparatively homogeneous; com- 

 posed mostly of tracheids fairly uniform in structure and arranged 

 in definite radial rows; barely visible under lens. Growth rings 

 usually quite distinct on account of the abrupt change in density 

 and in color between the late wood of one year's growth and the 

 early wood of the next (see p. 40). Wood parenchyma (resin 

 cells) and resin ducts present or absent. Rays very fine, scarcely 

 visible without a lens. W^oods with or without pronounced 

 resinous odor and taste. 



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