60 THE BOOK OF FORESTRY 



haps the most common defects in wood. They repre- 

 sent the portion of a branch which is imbedded in the 

 tree and are especially common toward the heart. When 

 trees have grown in a dense stand the lower branches 

 soon die, are broken off by wind or ice and the later 

 growth rings cover the knots up. That is why a forest 

 of old veterans produces clear lumber on the outside 

 while the core of the trunk contains many knots. 

 Another common defect in lumber is what is known as 

 a "shake," which is the separation of the fibers in the 

 trunk. This may occur as a split running from the 

 center out along the radius. If several clefts are 

 present, the condition is known as "star shake." Another 

 type of this defect is the "cup" or "ring shake." This 

 is caused by the separation of one or more growth rings 

 from the adjacent rings. When a log with cup or ring 

 shake is sawed up the shaky portion separates from the 

 remainder and a bad case may completely spoil the log 

 for lumber. Such defects are common in nearly all 

 overmature trees, and while usually they occur only 

 in the butt log, they may affect the whole trunk and 

 some of the larger branches. 



Possibility of Substitution. No other nation uses 

 wood as freely as ours and the remark that the civili- 

 zation of North America is founded upon wood is as 

 true today as formerly. Today we are using two hun- 

 dred and sixty cubic feet of wood per year for each 

 citizen of our country, an amount twice as much as 

 was used fifty years ago and six times as much as is 

 used per capita in the German Empire. With the rapid 

 growth in the steel and concrete business which has 

 taken place during the past decade the prediction has 

 been freely made that these materials would rapidly 

 replace wood. While it is true that bridges, houses, 



