14 Bulletin 194 



It is desirable in many instances to add other characters to lessen 

 the likelihood of confusion, in cases where the characters chosen are 

 not distinct, and in order to show the user that he is on the right track. 

 Thus, in the example just given, green color and slate color might be 

 confused owing to certain defects of the eye, to a coating of dust or 

 deficiencies of the light. Hence we would be justified in adding to the 

 above statements additional distinguishing characteristics. Thus : 



bb. 



c. Trimmings green color; gable roof Jones' house 



cc. Trimmings slate color; mansard roof Broivn's house 



The keys in this bulletin are constructed on these principles. 

 They are not always as simple as the illustration just used, but if the 

 reader has mastered the house illustration he will have little or no 

 trouble with the larger keys. In order that the usage of the keys may 

 be made the more clear, the following example, couched in language 

 using the personal pronoun, is set forth at some length. The reader is 

 advised to trace it from beginning to end as a ready means of familiar- 

 izing himself with the use of and possibilities of the key system. 



Suppose that during a summer stroll you come across a large tree 

 with rough, flaky bark and thin, lobed leaves which you do not know. 

 Turning to the Summer Key to the Genera on pages 16 to 19, you find 

 first a Leaves simple, and contrasted with this aa Leaves compound. 

 Obviously the leaf is simple and the genus sought lies in that portion of 

 the key preceding aa, i. e., under a. The subdivisions, b, and bb, under 

 a afford you a choice between Leaves needle-shaped, awl-shaped, 

 strap-shaped or scale-like and Leaves broad and flat. The leaf being 

 broad and flat you pass onwards in the key to c and cc under bb. Here 

 you have a choice between Leaves alternate or clustered and Leaves 

 opposite. Inspection shows the arrangement to be alternate, and you 

 know that the genus sought lies in that portion of the key which lies 

 between c and cc. Passing to d and dd under c you are offered the 

 choice between Margin of leaves entire or only slightly undulate and 

 Margin of leaves serrate, toothed or lobed and your observation clearly 

 indicates that the leaf is neither entire nor undulate, hence are in dd 

 class. Under dd you may choose between e. Margin of leaves serrate 

 to toothed and ee. Margin of leaves distinctly lobed. The leaf being 

 deeply lobed, you know that the genus sought is one of five lying 

 between ee and cc, all of which have lobed leaves. To make the de- 

 termination, you must look for the fruit, since / and ff under ee give a 



