ECONOMIC WOODS OF THE UNITED STATES 99 



b Pores small to minute,* often indistinct without lens 

 (especially in dense woods), mostly very numerous and 

 well distributed throughout growth ring. Vessels not 

 conspicuous. 



a 1 Woods dense to moderately so.f Rays variable from 

 fine to broad. (For b 1 , see p. 105.) 



a 2 Pores in radial lines, not crowded laterally. Wood 

 parenchyma in tangential lines. 



a 3 Lines of wood parenchyma visible with lens on 

 moist cross section. Pores in early wood visible 

 to unaided eye. Wood dense, difficult to split. 

 Vessels with spirals; perforations simple; pits into ray cells 

 simple or nearly so. Wood fibres without spirals; pits 

 bordered. 



a 4 Rays all very fine, indistinct. Pores near pe- 

 riphery of growth ring minute and in groups 

 which appear to the unaided eye as white dots. 

 Growth rings sometimes sinuous; distinct. 

 Color light brown or roseate. Sp. gr. .83. Rays 

 heterogeneous in part. Hop Hornbeam, Ironwood, 

 Ostrya virginiana Koch. (N, C) (Plate V, Fig. 6). 



b 4 Some of the rays broad, aggregated. Pores in 

 late wood sometimes as in preceding. Growth 

 rings always sinuous; distinct or fairly so. 

 Color yellowish white. Sp. gr. .73. Rays homo- 

 geneous. Blue Beech, Water Beech, or Horn- 

 beam, Carpinus caroliniana Walt. (N, C). 60 



b 3 Lines of wood parenchyma not visible with lens. 

 Pores not visible without hand lens; arranged in 

 regular radial lines; no white dots. Rays distinct. 

 Growth rings regular; rather indistinct. Wood 

 moderately dense; sp. gr. .51-. 66, average .58; 

 fairly easy to split. Color chalky white, often 



* In a few woods of this group, particularly cottonwood and black willow, 

 the pores, at least in early wood, are readily visible, but their abundance and 

 the softness of the wood permit no confusion with the preceding group. 



t A partial exception occurs in the case of Nyssa, some of the species of 

 which produce light and soft woods. 



