96 ECONOMIC WOODS OF THE UNITED STATES 



ceedingly heavy (sp. gr., 1.14), harder than horn, 

 strong, brittle, cross-grained, very difficult to work. 

 Pores somewhat variable in size, small and inconspic- 

 uous, scattered, solitary; usually filled with, dark-green 

 resin. Rays very fine, uniseriate, deeply colored, almost 

 invisible; in perfect horizontal series, producing cross 

 lines very distinct under lens. Wood parenchyma in 

 numerous, fine, wavy tangential lines. 



Lignum vitse. Guaiacum sanctum L. (T). 



c' Color light brown or straw. Wood very hard (sp. gr., 

 .83), heavy, tough, and strong like hickory; fibres much 

 interlaced; wood rather difficult to work. Pores variable 

 in size, conspicuous, irregularly distributed in wavy lines 

 or groups, open. Alternate bands of very dense and less 

 dense wood produce zones somewhat resembling annual 

 rings. Rays very fine, not deeply colored, almost 

 invisible; irregularly distributed. Wood parenchyma 

 not in tangential lines. 



Blue Gum. Eucalyptus globuliis Lab. (Ps, T).*^ 



2 Growth rings usually distinct, corresponding to annual 

 periods; late wood recognized by its greater density, tan- 

 gential flattening of the outermost rows of fibres, and some- 

 what fewer or smaller pores. 



a Pores comparatively large in early wood, distinct to unaided 

 eye, diminishing in size and number toward periphery of 

 growth ring; often approaching ring-porous. 



a^ Rays fine, 1-4 seriate, few to 30 cells high, scarcely 

 visible to unaided eye; mostly homogeneous. Pores 

 solitary or in radial groups of 2-5; often La diagonal 

 rows. Vessels without spirals; tyloses present, very 

 dark-colored. Wood parenchyma in numerous, very 

 fine, short, tangential lines; chambered cells bearing 

 crystals common (Plate IV, Fig. 6). 



a^ Wood heavy and hard, moderately stiff and strong. 

 Odor mild, but characteristic. Color rich dark or 

 chocolate brown. Sapwood rather thin to thick. 

 Black Walnut. Juglans nigra L. (C, A).' 



