36 BULLETIN" 327, U. S. DEPARTMENT OF AGRICULTURE. 



of the leaves bear lines of minute pores (stomata), which give a 

 whitish or pale bluish tinge to the foliage. 



The cones (PL XXIII) are mature early in September, when they 

 may be either very pale olive-green with an ashen tinge, or clear 

 chrome-yellow green, while sometimes they are purple. They vary 

 in length from about 3| to 4 \ (sometimes nearly 5) inches. The 

 bracts, attached to the back of the cone-scales (PL XXIII, a), are 

 sometimes rather narrow and oblong, or occasionally broad and 

 rounded, the free end having a small, wide-based point extending 

 from its center. The seeds (PL XXIII, h) are a dingy yellow-brown 

 with shiny, clear, rose-tinted wings. The seed-leaves are commonly 

 6 in number, or occasionally 7. 



White fir wood varies in color from whitish to a pale indistinct 

 brown, being soft, rather wide-ringed, and straight-grained. In 

 weight it ranks third among other Rocky Mountain firs, a cubic foot 

 of dry wood weighing about 22^ pounds. It works easily, and is 

 strong and hard enough to be useful for saw timber, for which it is 

 cut to some extent. Many large trees are, however, affected with 

 "punk-rot" or are wind-shaken, defects which render much of the 

 old stands useless for commercial purposes. 



OCCURRENCE AND HABITS. 



White fir is for the most part a tree of moderate altitudes, occur T 

 ring in general at elevations between 6,000 and about 11,000 feet, but 

 more frequently at altitudes between 7,000 and 9,000 feet. It usually 

 grows on north slopes, and is especially abundant on benches an$ 

 the sides of moist canyons of these aspects (Map No. 9). White fir 

 is less particular as regards aspect in the North than in the South. 

 It thrives in almost all fairly moist, well-drained soils, except heavy 

 clays. The best growth, however, occurs in fairly deep, rich, moist 

 gravelly or sandy loam soils. Frequently, nevertheless, it occurs on 

 dry, nearly pure, coarse, disintegrated granite, and even among 

 bowlders, but it is of much smaller size in such situations. White 

 fir requires less atmospheric and soil moisture than any of our other 

 firs, yet its best growth is always in cool, moist situations. 



Abies concolor never forms pure stands of mature trees over large 

 areas, although it occurs frequently in nearly pure growths of lim- 

 ited extent. Douglas fir is very commonly associated with white fir, 

 and alpine fir, Engelmann spruce, and aspen are found with it more 

 or less. Occasionally it occurs with western yellow pine and limber 

 pine. The frequent dominant stands of young white fir, which occur 

 mingled with Engelmann spruce or J)ouglas fir, usually give way in 

 numbers to the latter species when the pole stage is reached, so that 

 the white fir later constitutes a much smaller percentage of the 

 maturer stand than it did at the beginning. 



