BALSAM FIR. 
25 
BARK. 
The bark on the stump of a mature balsam fir is seldom thicker than 
0.7 of an inch and in the top, at a diameter of 4 inches, seldom more 
than 0.3 of an inch. In volume the bark amounts to about 10.5 per 
cent of the whole tree. On thrifty trees it is very smooth, except for 
swellings or "blisters," which contain a clear liquid from which the 
so-called Canada balsam is obtained by distillation in water. In 
abundant seed years balsam blisters are very small, probably due to 
the tree's use of most of the foodstuffs for the production of seed. 
Abnormally thick, rough, or scaly bark of an ashy color, accompanied 
Fig. 3.— Leaf structure of Abies balsamea; D, ducts; B, bundle sheath; F, fibro- vascular bundle; M, 
mesophyll; E, epidermis; S, strengthening cells. 
by swelling of the bole, is an almost infallible sign that the tree is 
rotten at those parts. The natural color of the bark in young trees 
is a dull, faded green, mottled with patches of gray. With age the 
bark becomes entirely gray and slightly scaled, but not the dull ashy 
gray of a defective tree or the shaggy moss and lichen-covered scale 
of a slow-growing balsam in the swamp. 
ROOT SYSTEM. 
Whether grown in deep or shallow soils, balsam fir produces a very 
superficial root system, penetrating to a depth of about 2 or 2.5 feet. 
Taproots, if developed at all, soon die and rot .away, especially in 
20137°— Bull. 55—14 i 
