58 



A MILL SCALE STUDY OP WESTERN YELLOW PINE. 



22 



26 



30 



34 



38 



42 



46 



DIAMETER BREASTHIGH INCHES 



FIG. 60. A comparison of high, intermediate and low grade curves, which show 

 the total per cent sawed out of each grade from immature trees of different diameters 

 breasthigh. Note the increasing per cent, indicated by the high grades, and the 

 decreasing per cent indicated by the low grades. This is due to quality increment. 

 In no case does the volume in board feet of low grades contained in a tree become 

 smaller, or even hold constant as the tree increases in size ; but the fractional part 

 that a certain grade is of the whole merchantable volume may hold constant, decrease 

 or increase, all depending upon the quality of the successive layers of wood formed 

 during growth. 



