ECONOMIC WOODS OF THE UNITED STATES 95 



of collected in decided ring or zone in the early wood; occa- 

 sionally more numerous and very often somewhat larger in the 

 early wood. Growth rings principally defined by the greater 

 density .of the late wood or by the radial flattening of the 

 outermost rows of wood fibres; often indistinct; sometimes 

 absent. 



1 Growth rings absent or indistinct; when present not cor- 

 responding to annual periods and not separable into early 

 and late wood. 

 a Broad rays present. 

 a^ Color light to dark brown, sometimes tinged with red. 

 Wood very heavy, hard, strong, and tough ; not easy to 

 work. Pores slightly variable in size; rather small but 

 distinct, arranged in radial rows or groups usually con- 

 tinuous from year to year. Large rays mostly rather 

 low, broad; often appearing on tangential surface as 

 aggregations of small rays interspersed with wood 

 fibres. Evergreen Oak Group.^^ 



a^ Wood parenchyma in very distinct tangential lines. 

 Tanbark Oak. Quercus densifiora H. & A. (P)*°; 

 hypoleuca Eng. (Rs). 



b^ Wood parenchyma not in tangential lines or, if so, 

 not distinct. Live Oaks. Q. virginiana Mill. (S), 

 chrysolepis Liebm. (Ps), agrifoUa Nee. (Ps). 

 b Broad rays absent. 



a^ Color rich reddish brown to light brown; widely vari- 

 able. Wood variable from light and soft to very hard, 

 heavy (sp. gr., .56-.88), and strong; brittle; often 

 highly figured. Pores uniform in size, rather large and 

 conspicuous, equally distributed, solitary or in radial 

 groups of 2-3; often filled with dark-red resin. Rays 

 fine but distinct, producing silver grain on radial surface ; 

 deeply colored; heterogeneous; often in horizontal 

 seriation producing rather imdulating cross lines on 

 tangential surface. Wood parenchyma in rather widely 

 separated conspicuous tangential lines, limiting growth 

 rings. Mahogany. Swietenia mahagoni Jacq. (T).*' 



b' Color dark yellowish brown with decided greenish tinge, 

 often streaked; nearly black in old trees. Wood ex- 



