BALSAM FIE. 



25 



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 ''bUsters," 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 smaU, 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; Jtf, 

 mesophyU; E, epidermis; S, strengthening ceUs. 



by swelling of the bole, is an almost infaUible 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 soUs, balsam fir produces a very 

 superficial root system, penetrating to a depth of about 2 or 2.5 feet. 

 Taproots, if developed at aU, soon die and rot away, especially in 

 20137°— Bull. 55—14 i 



