16 BULLETIN 327, U. S. DEPARTMENT OF AGRICULTURE. 



inches long (PL V, a), but usually about 3^ inches. They are ripe 

 by the middle or end of August, the thin, tough scales spreading 

 slightly and shedding their seeds during September. In color the 

 cones are a very light yellow-brown and rather shiny. A few of 

 the empty cones fall during the first winter, but the majority re- 

 main on the trees until late autumn of the second season. The 

 small 7 seeds (PL VI, a) are dull chestnut-brown and have pale 

 yellow-brown wings. Seed-leaves of the blue spruce vary in number 

 from 5 to 6 (PL V, c). 



The sapwood and heartwood are often very similar in color. 

 When distinguishable, the heartwood is pale brownish-yellow to 

 light straw color, while the sapwood is nearly white, the smoothed 

 surface of both having a silklike sheen. Seasoned wood is rather 

 light, weighing about 23 pounds per cubic foot, ranking fifth in 

 weight among our spruce woods. It is moderately soft, brittle, and 

 with narrow, often exceedingly narrow, rings of growth. Owing 

 to the limited supply and the commonly knotty character and other- 

 wise inferior quality of the wood, it is the least valuable of all of 

 our native species for commercial purposes. It is rarely used, ex- 

 cept locally for house logs, corral poles and posts, temporary mine 

 props, fuel, and occasionally for railroad ties. 



OCCURRENCE AND HABITS. 



Single trees, small groups, and scattered pure groves of limited 

 size occur along the immediate banks of streams flowing in deep 

 and shallow canyons, and in broad, open, grassy valleys. (Map 

 No. 4.) Occasionally single trees are found several hundred yards 

 away from streams and 200 to 300 feet above the water. The largest 

 trees are always found near water. Blue spruce grows in moder- 

 ately rich dry to moist gravelly, sandy, or rocky soils, at elevations 

 between about 6,000 and 8,500 feet, sometimes ascending to nearly 

 10,000 feet. It is associated mainly with Engelmann spruce, alpine 

 fir, and occasionally with narrow-leaf cottonwood. 



The light requirements of blue spruce are imperfectly known at 

 present, but it is closely similar in tolerance of shade to the Sitka 

 spruce, yet much less tolerant than Engelmann spruce, black spruce, 

 and red spruce. Seedlings and young trees endure but little shade 

 without a material check to their growth, the most vigorous and full 

 development occurring only in full light. 1 With top light saplings 

 and older trees are able to endure considerable side shade. 



Blue spruce is an abundant seeder, producing full crops of cones 

 at intervals of 2 or 3 years. The seed has a rather high rate of ger- 



iMuch disappointment is experienced by those who use this tree for ornament because 

 it does not continue to maintain a full, vigorous crown when planted under the shade of 

 older trees or in close groups. The best form can be produced only by planting single 

 trees, or groups of trees widely spaced, so that they will have full enjoyment of sunlight. 



