ECONOMIC WOODS OF THE UNITED STATES 103 



b 8 Color pale, often with greenish tinge. 

 Pith flecks very common, often abund- 

 ant. Sp. gr. .62. Soft or Red Maple, 

 A. rubrum L. (N, C, S); Silver Maple, 



A. saccharinum L. (N, C, S). 



b 3 Rays indistinct without lens. 



a 4 Wood mostly straight-grained, easy to split. 

 Growth rings usually distinct. Wood paren- 

 chyma scattered, sometimes in broken tangen- 

 tial lines in outer late wood and in a single 

 terminal layer usually visible as a faint white 

 line. Vessels without spirals; densely pitted with ex- 

 tremely small bordered pits with slit-like openings; perfora- 

 tions scalariform; pits into ray cells half -bordered. Rays 

 1-5 cells wide; homogeneous. Wood fibres with bordered 

 pits. Birch. 55 



a 5 Wood mostly heavy, hard and strong. Color 

 brown tinged with red, sometimes deeply 

 reddish; often figured. Pith flecks rare. 

 a 6 Specific gravity .69-. 82, average .76. Rays 

 widest of genus, bluntly tapering; cells round 

 (tangential section). Sweet, Black or Cherry 

 Birch, Betula lenta L. (S, C, N).* 

 b 6 Specific gravity .58-.72, average .66. Rays 

 narrower, cells flattened laterally (tangential sec- 

 tion). Yellow Birch, B. lutea Michx. f. 

 (N, C). 

 b 5 Wood considerably less dense than in pre- 

 ceding group; sp. gr. average .58-60. Color- 

 less or light brown. Pith flecks common. 

 a 6 Pores rather large, readily visible to unaided 

 eye. Wood rather coarse-textured; some- 

 times cross-grained. Sp. gr. .55-. 60. River 

 or Redf Birch, B. nigra L. (S, C, N). 



* The woods of Betula lenta and B. lutea appear on the market together 

 without distinction as to species, and have identical uses. The former is some- 

 what harder and stronger as a rule. 



t The names "red birch" and "white birch" are often used commercially 

 to designate the heartwood and sapwood, respectively, of Betula lenta and B. 

 lutea. 



