FOREST UTILIZATION 65 



(b) Nail holding power, which is said. to be excellent 



in chestnut, white pine and hemlock. 



(c) Twisted growth, which is frequent in .chestnut, 



Italian poplar and horse chestnut. Certain twists 

 are due to a hypertrophical growth of the tissue 

 and are highly prized by the trade under the 

 names of birdseye maple, curly poplar, curly 

 walnut, curly cherry and curly ash etc. It is im- 

 possible to say whether a standing tree is "curly" 

 or not. Sap-sucking woodpeckers may start the 

 "freak." 



(d) Knots check the value of lumber. A standard knot 



is a sound knot, the diameter of which varies ac- 

 cording to local inspection from ij4" to 1^4". 

 Dry, dead and unsound knots throw a board into 

 the mill cull pile. Usually, the knotty part of a 

 log is sawn into dimension stuff. The core of a 

 log, even in yellow poplar, necessarily shows 

 knots, since there is no height growth without 

 simultaneous formation of side branches. 



(e) The discoloration of the inner layers of certain 



species which are not classed as heartwoods 

 (beech and maple) is a disease often found in old 

 trees and causes rejection for certain applications 

 in the trades (impregnation). 



CHAPTER V. MANUFACTURING INDUSTRIES. 



XVII. THE SAW MILL. 



A. The saw. 



Three kinds of log saws are used: 

 I. Straight saws, viz : 



Vertical straight saw; 

 Gang saws ; 

 Horizontal frame saw. 

 II. Circular saws, viz. : 



Solid tooth single saw ; 

 Solid tooth double saw ; 

 Inserted tooth saw. 

 III. Band saws, viz. : 



Single cutting band saw ; 

 Double cutting band saw. 

 I. Straight saws. 



(a) Single vertical straight saw. At the toothed 

 edge this saw has a thickness of from 5 to 10 

 gauges. Its blade is 8 inches wide and at least 

 twice as long as the log diameter. 



