ROLE OF THE MICROSCOPE 191 



Our mahoganies are from different genera, but resemble enough 

 in structure. 



[g) Where, as in dye woods, etc., we use barks, roots, etc., it is an 

 expert job to judge and grade, and the practice has long adapted 

 scientific methods here. 



y. Study of structure does not pretend to replace the ordinary 

 grading, but to add a more reliable factor. 



8. Hand lens examination of white fir by two men did cover about 

 9 cords of stuff in one day at Detroit and settled a difference of about 

 $1,000 on a load of pulpwood supposed to be all spruce. 



!>. The most common or extensive use of the study of structure 

 in practice is its value in effective grading woods ; that is, in appreciating 

 their value for different uses, and understanding their behaviour as to 

 strength, elasticity, toughness, shrinkage, etc. 



A man who studied woods in a detailed way will never make the 

 mistake of passing a lot of southern oak, so poor that chair posts 

 broke without any load when the chair tipped over. 



10. Sum up : Study of structure and key based on structure are very 

 useful in practice and the chief trouble has been thus far that the mat- 

 ter has not been taught and sufficiently published. Such excellent 

 pictures as Bailey's will go a long way to help this. But with it all 

 must come, as he says, full appreciation on the part of writers just how 

 far a particular distinction actually distinguishes. A lot of fine phrases 

 of "annual rings slightly wider" affairs will not help much. 



