ARTIFICIAL KEYS, HOW MADE AND USED 



An artificial key is a scheme for easily and quickly identifying 

 any unknown object under consideration. This bulletin being 

 devoted to the trees of Michigan, the keys to be found herein 

 are intended to make it possible for any person, even if his botan- 

 ical training be meager, to determine what trees grow about any 

 home or farm, city park or woodlot in the state. With certain 

 modifications and limitations they may prove useful in other 

 localities as well. Since many people are unfamiliar with the 

 construction and use of keys for identification, it will be the pur- 

 pose of the following paragraphs to briefly outline the principles 

 of construction and the manner of using the keys to be found 

 here. 



The keys are based on the most striking similarities and 

 differences which the various parts of trees twigs, buds, leaves, 

 etc. show, i. e., those characters which stand out in bold relief, 

 which catch the eye at first sight. Two alternatives are presented, 

 either a character is or is not present ; these are the only choices 

 possible. Indeed, further divisions are unnecessary and only lead 

 to confusion and possible oversight. The two diametrically 

 opposed characters are said to be coordinate in rank. In the 

 keys they are preceded by the same letter or letters (a and aa or 

 b and bb, etc.) and are set at the same distance from the left 

 margin of the page. Often a and aa, or b and bb are further 

 divisible into other groups; in every case the characters arc 

 opposed (a positive and a negative) and are given coordinate 

 rank. It is desirable for mechanical reasons to divide the main 

 divisions of the key more or less evenly, but this is not always 

 feasible, nor should it be religiously adhered to. 



Suppose as a concrete example that it is desired to construcr 

 a key to distinguish five houses in a city block. Three of these 

 are of wood construction, two are of brick, and of the three 

 wooden houses two are painted white and one brown. We may 

 classify them as follows: 



xvin 



