6 THE PRINCIPAL SPECIES OF WOOD. 



The figures established by the United States Division of 

 Forestry and alluded to in item I, page 4, appear, so far as 

 they exist, upon the following pages. Where they do not 

 exist, the leading spaces set apart for them are left vacant for 

 other insertions as preferred. All coefficients are in pounds 

 per square inch. Fractions of pounds in weight and lower 

 figures in coefficients have been omitted as superfluous. 



It is not always easy to determine the species of living 

 trees, because forms in the forest differ from those in the open, 

 because bark varies with age, and because fruit and leaves of 

 many trees are lacking in the winter. It is easier to tell 

 genus than species that a tree is an oak, than whether it is a 

 red or a pin oak. Experience is required in this connection. 



Trees are divided into two general divisions known as 

 Exogens and Endogens.* 



* This division coincides with that by which they are separated into Dicoty- 

 ledons and Monocotyledons. 



