82 ECONOMIC WOODS OF THE UNITED STATES 



b^ Colo r red to rprlrfiph hrnwn Texture coarse and 



harsh. Western Larch. L. occidentalis 'Nutt. (R) . 



b' Resin ducts somewhat larger, usually visible to ^nairlorl 



_e^; oval in cross section. Sapwood rather thick. 



Spiral markings on the tracheids, at least in early wood; 



marginal ray tracheids with spirals. 



a^ Grain us uall y Rtra.ijyht: sometimes wavy. Wood of 

 two kinds: (1) growth rings narrow, .wood reddish 

 _j;ellow m^color and of fairly un iform texture.: rather 

 light and soft, easy to work. "(2) Growth rings wide, 

 wood^arkj;ed i n color and of uneven texture : early 

 wood open and weak, late wood flinty; difficult to 

 work. 



Douglas Fir. Pseudotsuga taxifolia Brit. (P, R).^' 



b^ Grain usuall y not stra.ig-ht - wood often cross-grained; 

 color alwavs red . Wood usually less dense, rays 

 more numerous, and the pits on the ray-parenchyma 

 cells larger than in the preceding. 



Red Fir. P. macrocarpa Mayr. (P). 



2 Without clea r demarcation in color between heartwood and 

 sapwood. 



a Resin ducts mostl y_sniaIl, scattered; epithelium thick- 

 walled; tyloses often present. Resin cells absent. Tra- 

 cheids without spirals.* Wood mo stly light and sg tL fine 

 and even-textured. Spruce." 



a' C olor white or very light: uniform throughout. Little 

 contrast in density between early and late wood. Resin 

 ducts scarcely visible without lens, being of same color as 

 surrounding wood. 



a^ Growth ringsjnostlsL-widert 



White Spruce. Picea canadensis Mill. (N). 



* The sporadic development of wood parenchyma on the outer surface of 

 the late wood, and the occurrence of spiral thickenings of the tracheids in 

 both early and late wood of Picea have been noted by Bailey, loc. cit. 



t Owing to the fact that rate of growth is largely determined by external 

 factors, any attempt to classify woods on a basis of width of ring is at best 

 unsatisfactory and is resorted to here only because constant features of dis- 

 tinction are apparently wanting. 



