PREFACE v 



matter to determine the approximate size of any 

 leaf. 



Throughout the key occasional reference is made 

 to cuts which illustrate the points under con- 

 sideration. 



After determining the name of a tree it is an 

 excellent plan to go over the key again and make 

 careful note of the particular characters that were 

 used to separate it from other trees, especially the 

 near allies. Also dry a leaf under moderate pres- 

 sure and keep it for future reference. If these 

 suggestions are followed systematically and con- 

 scientiously most of our common trees can soon be 

 recognized at sight. The main object of this key 

 is merely to guide the student through the prelimi- 

 nary stages of this recognition. A true knowledge of 

 trees must be derived primarily from accurate and 

 abundant study of the trees themselves. 



To those who have had little or no experience 

 in determining plants by means of botanical keys 

 the following suggestions will be helpful. 



Take the key with you into the field or wood. 



Look over the tree and select typical (or average) 

 leaves and twigs before attempting to use the key. 

 As a rule only these should be considered. In most 

 cases these need not be detached, and they should 

 not be when there is any suspicion that objection 

 might be raised to such a procedure, as might be 



