OUR FORESTS 19 
use. The products manufactured by forest industries have a yearly 
value of more than 3 billion dollars, not including paper and paper 
products, and in the value of its products the group ranks sixth among 
the leading industries of the United States. 
From the forest also comes the raw material used in the manufac- 
ture of paper and numerous other products. The basis of paper is 
pulp made from fibers of cellulose, that remarkable material which 
forms the framework and other construction materials of plants. 
Wood is the most abundant source of cellulose in the plant world, for 
more than one-half of its substance is cellulose fiber. Wood pulp is 
today the leading paper material, although paper has long been made 
from linen and cotton rags. 
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FIGURE 12.—Lumber seasoning at the mills. 
Felled trees are cut into logs for transportation to the mill, where they are 
trimmed and cut into boards. After the boards have been edged and trimmed, 
they are sorted and sent to the lumber yard to be piled and seasoned. 
Four commercial processes of making paper from wood are in 
general use: three chemical—the sulfite, sulfate, and soda processes; 
and one mechanical—the ground-wood process. In each of the 
chemical processes the chipped wood is cooked with a chemical under 
steam pressure in a specially designed cooker, or digester. This 
process removes the portion of the wood known as lignin, which is 
the material that binds the cellulose fibers together. In the ground- 
wood process the uncooked wood is ground into a pulp. Each 
process is adapted to the manufacture of certain grades of paper or 
to the pulping of certain woods, the stronger and better grades com- 
ing from the three chemical processes. Among the woods suitable 
for pulping are spruce, hemlock, southern yellow pine, poplar, balsam 
fir, jack pine, white fir, beech, birch, maple, gum, and larch. 
The United States uses more paper than all the rest of the world. 
In 1936 our consumption of paper products amounted to no less 
