36 BULLETIN" 327, U. S. DEPAETMENT OF AGKICULTUKE. 
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 J to 4J (sometimes nearly 5) inches. The 
bracts, attached to the back of the cone-scales (PL XXIII, &), 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 22J 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. 
OCCUKRENCE AND HABITS. 
White fir is for the most part a tree of moderate altitudes, occur- 
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 and 
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 Douglas 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. 
