22 BULLETIX 327, U. S. DEPARTMENT OF AGRICULTURE. 
of the middle-crown branches (PL VIII, h) and of the upper or cone- 
bearing branches (PI. IX), while the thinly set leaves of the terminal 
shoot or ** leader " are strikingly different from all of the other 
foliage (PL VIII, a). In length the leaves vary from about li 
inches on the lower and middle-crown branches to about five-eighths 
of an inch on the topmost branches. A slightly magnified cross sec- 
tion of the leaf shows two resin ducts, one in each end of the section 
(edge of leaf), slightly nearer to the lower surface of the leaf. 
Mature cones (PL IX), which are fully grown and ripe by Sep- 
tember, are from 2 to about 4^ inches long and from seven-eighths 
of an inch to lffc inches in diameter. At first the ripe cones are exter- 
nally deep purple, which later become paler as the scales are loosened 
by drying and fall away from the cone's central axis (PL IX, c) . The 
bracts attached to the backs of the cone scales (PL IX, a) are only 
about one-half as long as the scales. Sometimes, however, the points 
of all of these bracts extend slightly beyond the ends of the cone scales, 
while in rare instances some of the cones of a tree may have extended 
bracts and other cones hidden bracts. The seeds (PL IX, h) are pale 
yellowish-brown, as are also the shiny wings. 1 
Balsam fir wood is usually of very light weight, soft, and brittle. 
It is rather wide-ringed in the faster-growing trees of open stands, 
and narrow-ringed in the slower-growing trees of dense stands. Sea- 
soned wood weighs approximately 23.8 pounds per cubic foot, rank- 
ing second in weight among the other Rocky Mountain fir woods. 
The sapwood is whitish and from 1 to 2 inches thick, while the heart- 
wood is light yellowish brown, sometimes marked with yellow areas. 
In the central and eastern part of the tree's range the wood is ex- 
tensively used, in mixture with spruce wood, for paper making. It 
is also much used for box boards, being rarely cut into other lumber 
because of its soft texture, knotty character, and lack of durability. 
OCCURRENCE AND HABITS. 
Throughout its wide range balsam fir grows in soils and under 
climatic conditions that are quite dissimilar (Map Xo. 5). In the 
main, however, it demands an abundance of soil moisture and a 
humid atmosphere. Lack of these conditions limits its occurrence 
or greatly impairs its growth. It is most common and of largest 
size in rich well-drained bottom lands and on adjacent high ground 
about lakes and water courses, being less common and of smaller size 
in swampy and low ground, on low hills and benches, on high ridges, 
and at or near low timber line. The vertical range of balsam fir 
1 The only other Rocky Mountain fir that could be confused with the balsam fir, and 
then only in Canadian territory, is the alpine fir, which is somewhat similar in siae and 
general appearance. The larger, longer, crowded, upright lower-branch leaves of alpine 
fir, however, and the horny, little-broken trunk bark of large and medium size trees serve 
to roughly distinguish this species from balsam fir, the lower-branch leaves of which are 
commonly arranged on two sides of the twigs, while its trunk bark is loosely scaly. 
