32 BULLETIN 55, U. S. DEPARTMENT OF AGEICULTUfefi. 



spruce, has no distinct heartwood and sapwood. Its narrow pith 

 rays of a pale or whitish color are scarcely visible. Air-dry wood of 

 balsam fir is light, weighing 24 pounds per cubic foot, as compared 

 with 28 pounds for spruce. Wlien completely dry, it has an average 

 density of 0.38, and loses about 4 per cent of its volume in seasoning. 



COMPARATIVE LENGTH OF WOOD FIBERS OF BALSAM FIR AND SPRUCES. 



Table 7 gives the average, maximum, and minimum lengths of 

 the wood fibers of balsam fir and the northeastern spruces. 



Table 7. — Average, maximuvi, and minimum lengths of fibers of balsam fir and the 



northeastern spruces. 



Species. 



Length of wood fiber (mfllimeters). 



Average. 



Maximum. 



Minimum. 



Balsam fir (Ahies baJsamea) 



White sDruce (Picca canadensis) 



Red spruce {Picea rubens) 



Black spruce (Picca mariana) .. 



2.518 

 3.556 

 3.233 

 2.599 



3.750 

 4.704 

 4.158 

 3.738 



1.680 

 2.520 

 1.890 

 2.142 



GROWTH. 



Balsam fu' is a fairly rapid growing tree, though not as rapid as 

 tamarack and white pine. 



HEIGHT GROWTH. 



Balsam fii- has a period of comparatively slow growth, which, under 

 favorable light conditions, lasts only for the first five yesiYS of its life ; 

 a period of rapid growth then sets in and continues until the tree is 

 60 years old. From then on the growth ui height begins to decline, 

 and at 80 years the growth is practically at a standstill. At 150 

 years it stops altogether. The most rapid growth in height takes 

 place between the twentieth and fortieth years. 



The slow growth of balsam fir for the first five or six years is an 

 inherent characteristic of the species, and occurs even under the best 

 light conditions. Beneath the shade of other trees, however, the 

 period of slow growth is often extended to 25 years or more because 

 of the retarding efTect of the shade. 



