iv PREFACE 



a tree are exactly alike and that there is often a 

 wide range of shapes on the same tree. For this 

 reason the leaf outline shown (which is made from 

 a fairly typical leaf as understood by the authors) 

 may not be quite representative of what would be 

 called a typical leaf of that species growing under 

 different conditions, or in a different locality. 



The bark of most trees is characteristic, but in 

 many species, unfortunately, these characters can- 

 not be brought out as clearly as could be desired 

 in a halftone of the size used here. A consistent 

 attempt has been made to illustrate only certain 

 representative types. In certain cases, however, 

 bark illustrations of several allied species of a group 

 or genus are given. A full series seems hardly 

 necessary, as the key is based primarily upon leaf 

 characters. 



Technical terms, to a large extent, have been 

 eliminated. For the explanation of such as are 

 used see the glossary on page 149. The geographic 

 ranges given in the key must be interpreted as 

 general rather than precise, as no attempt has 

 been made to indicate the exact known limits for 

 any species. Beside each outline drawing an inch 

 scale, reduced in size to correspond with the reduc- 

 tion of the leaf, is shown. In a few cases a quarter 

 inch scale is used, but in all such cases the scale 

 is clearly so marked. By this device it is a simple 



