76 ECONOMIC WOODS OF THE UNITED STATES 



lower walls irregularly thickened, dentate to reticulate * (Figs. 

 6, 7, pp. 27-28). Pits rarely present in tangential walls of 

 the late wood. Pitch Pine Group. 



a 3 Ray parenchyma cells in early wood with 1 or 2 large simple 

 pits in each cross-field (Fig. 6, p. 27). Wood rather 

 light and soft, variable, fairly strong, medium- 

 textured, not highly resinous. Sp. gr. .42-.54. 

 Red Pine Group.j Red or Norway Pine, P. resi- 

 nosa Ait. (L). 6 



b 3 Ray parenchyma cells in early wood with 3-6 (occasionally 

 more) small, irregular, simple (rarely semi-bordered) pits in 



each cross-field (Fig. 7, p. 28). Yellow Pine Group. 



a 4 Woods variable from light and soft to moder- 

 ately heavy and hard. Western Pines. 



a 5 Wood fairly uniform, soft, not highly resin- 

 ous, light-colored. Sp. gr. .35-.47. Tangen- 

 tial surface showing conspicuous " pebbly " or 

 " dimpled " grain. Lodgepole Pine, P. con- 

 torta Loud., or P. murrayana "O.C." (R, P). 7 



b 5 Wood variable from light, soft, non-resinous, 

 and nearly white to fairly heavy, hard, res- 

 inous, and reddish-brown in color. Sp. gr. 

 .39-. 60. " Pebbly " grain not characteristic 

 though occasionally present. Western Yel- 

 low Pine, Western Pine, California, New 

 Mexico or Arizona White Pine, Western Soft 

 Pine, Bull Pine, P. ponderosa Laws.| (R, P;. 8 



* The very irregular thickenings of the upper and lower walls of the ray 

 tracheids are peculiar to the pitch pines. Spiral markings and other irregu- 

 larities of the wall found occasionally in the ray tracheids of certain other 

 conifers are quite distinct from the heavy sculpturing in the ray tracheids of 

 the pitch pines. 



t The microscopic structure of P. rcsinosa characterizes also one Asiatic 

 and two European pines which are being planted to some extent in the United 

 States, namely, Japanese Red Pine, P. densiftora S. & Z., Scotch Pine, P. 

 sylvestris L., and Austrian Pine, P. laricio Poir. 



J Included under this name are closely related forms whose woods are not 

 distinguishable. The softest grades of the wood are from the outer portions 

 of large, ovc -mature timber. 



