PICEA 289 



8. P. pungens, Engelm. 

 Blue Spruce. Colorado Spruce 



Transverse. Growth rings broad. The very thin and often barely distin- 

 guishable summer wood gradually passing into the spring wood ; the 

 tracheids very unequal and often much compressed radially. Spring 

 tracheids hexagonal, very thin-wailed, uniform in regular rows. The 

 structure is very open throughout. Resin passages rather few, small, 

 and scattering, with small and very unequal, thick-walled epithelium 

 cells ; thyloses few or wanting. Medullary rays rather numerous and 

 broad, i cell wide, distant 2-9 rows of tracheids. 



Radial. Rays nonresinous ; the ray tracheids numerous and marginal, 

 rarely interspersed. Parenchyma cells chiefly straight, equal to about 

 7 spring tracheids ; the terminal walls coarsely pitted ; the upper and 

 lower walls medium and entire or conspicuously pitted throughout ; 

 the lateral walls with small, oval, bordered pits with an oblong orifice, 

 2-6 per tracheid, toward the summer wood reduced to 2, and finally 

 to i. Bordered pits numerous, in i row, elliptical or round; the round 

 orifice becoming lenticular in the summer wood. Pits on the tangen- 

 tial walls of the summer wood small, not numerous or prominent, 

 chiefly confined to the outermost walls. 



Tangential. Rays numerous, nonresinous, medium to high. The fusiform 

 rays narrow, the resin canal rather small, with thick-walled epithelium. 

 The ordinary rays contracted at the position of the occasionally inter- 

 spersed tracheids ; the parenchyma cells rather thin-walled, very equal 

 and uniform, oblong, rather narrow. 



A tree 30-46 m. high, with a trunk upwards of .90 m. in diameter. 

 Wood very light, soft, weak, close grained, compact, satiny. 



Relative specific gravity 0.3740 



Percentage of ash residue 0.38 



Approximate relative fuel value 37.26 



Coefficient of elasticity in kilograms on millimeters . . 553. 



Ultimate transverse strength in kilograms 194. 



Ultimate resistance to longitudinal crushing in kilograms 4128. 



Resistance to indentation to 1.27 mm. in kilograms . . 1267. 

 (Sargent) 



Along borders of streams in damp or wet soil, generally between 6000 and 

 9000 feet elevation, and never forming forests. Rare and local. Valley of 

 the Wind River and south through the mountains of Wyoming, Colorado, 

 and Utah (Sargent). 



9. * P. nigra, Ait. 



Black Spruce 



Transverse. Growth rings rather broad, variable. The summer wood 

 usually much less than but upwards of one half the spring wood, from 

 which the transition is gradual ; the structure open. Spring tracheids 

 squarish-hexagonal, not very uniform, in regular rows, the walls 

 rather thin. Resin passages chiefly in the summer wood, equal to 2-4 



