by Rehder in his "Manual of cultivated trees and shrubs" as belonging 

 to the eastern part of his "Zones" I-VI and to the eastern and northern 

 parts of Zone VII. With a few exceptions the names are as given by 

 Rehder. There is listed only one genus poisonous to the touch, RHUS, 

 the sumac, whose toxic species have pinnately compound leaves with 

 entire margins and 7-15 leaflets. Other species of RHUS are harmless. 



When using the KEY start with section 1 ; read all the descriptions, 

 choose the one which fits the tree being studied, and then look up the 

 section indicated by the number opposite to the description. Proceed in 

 this way after the manner of a treasure-hunt until a name is reached. 

 As a rule the most striking character is placed first in the description. 

 If no characterization fits, take the best, or try all. Base the decision 

 on a comparison of several leaves, twigs, etc. ; not on one alone. Only 

 actual statements in the KEY should be considered. Frequently the 

 first part of a section is more detailed than those which follow it, either 

 because fewer trees are governed by it, or because it is describing a sin- 

 gle genus. Absence of these details in the other part or parts does not 

 imply their opposite ; it merely means that no general rule can be made 

 as yet. Whenever a term is unfamiliar or doubtful it should be looked 

 up in the EXPLANATION OF TERMS, as even common expressions 

 may here be used in a slightly different sense from that usually under- 

 stood. The EXPLANATION also gives suggestions for methods of ex- 

 amination. The species may be identified by using more detailed books, 

 such as those listed as references. 



The author will greatly appreciate the reporting of any mistakes or 

 difficulties. 



Grateful acknowledgement is made of the assistance of Mr. Percy 

 Wilson, Assistant Curator of the New York Botanical Garden, and of 

 the advice of Dr. Otis W. Caldwell of Columbia University. The de- 

 scriptions in Rehder's MANUAL and Trelease's plates were invaluable 

 in preparing the KEY. 



■th'~i V^' 



