78 ECONOMIC WOODS OF THE UNITED STATES 



stricted at intervals but rarely closed by tylosal outgrowths of 

 the epithelial cells; the latter are usually small, thick-walled, 

 rounded. Isolated wood parenchyma strands (resin cells) occa- 

 sionally found. Ray tracheids small, usually in single marginal 

 rows, sometimes showing minute spirals. Ray parenchyma pits 

 small and more or less piciform. Wood resembles that of 

 Southern Pines but for the most part is without very 

 pronounced resinous odor, usually less pitchy, and on 

 radial surface usually shows less distinct color con- 

 trast between seasonal growths. Color contrast be- 

 tween heartwood and sapwood distinct. Sp. gr. .39- 

 .68, mostly between .45 and .55. Growth rings more 

 or less undulating, showing on both cross and longitu- 

 dinal surfaces. Wood of two general classes : (1) Fine- 

 grained, fairly uniform-textured, moderately light and 

 soft, easy to work; color pale reddish-yellow; hence 

 the local name of " yellow fir." (2) Coarse-grained, 

 uneven-textured ; early wood open and weak, late wood 

 dense and flinty; color rather deep red, hence the local 

 name of " red fir." Douglas Fir, Spruce or Pine, 

 Oregon Pine, Pseudotsuga taxifolia Brit., P- douglasii 

 Carr., or P mucronata (Raf.) Sudw. (P, R). 14 

 b Resin ducts mostly small, inconspicuous, widely scattered 

 or in small tangential groups; appearing in late wood com- 

 monly as small whitish dots; usually open; epithelial cells small, 

 normally thick-walled, rounded. Isolated wood parenchyma strands 

 (resin cells) rare; terminal. Tracheids rarely with spirals. Ray tra- 

 cheids small, usually in single marginal rows, rarely with spirals. Ray 

 parenchyma cells thick-walled, abundantly pitted in upper, lower 

 and end walls; pits on lateral walls lenticular or slit -like, small, semi- 

 bordered, 2-6 in each cross-field in early wood.* 

 a 1 Wood variable, but mostly hard and heavy, with de- 

 decided contrast between seasonal growths; sometimes 

 decidedly pitchy. Sapwood thin with distinct line of 

 demarcation. Larch. 15 



* The woods of larch and spruce bear considerable resemblance microscopi- 

 cally to the woods of the foxtail and nut pine group. The}' can usually be 

 readily distinguished by the nature of the epithelial cells of the resin ducts, 

 being thin-walled and flattened in the pines and, with occasional exceptions, 

 thick-walled and rounded in the others. This is seen to best advantage in the 

 fusiform rays (tangential section). 



