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 codrdinate 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 are 
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 construct 
a key to distinguish five houses in a city block. Three of these 
are of wood construction, two are of brick, and of the two 
wooden houses one is painted white and one brown. We may 
classify them as follows: 
— XVIII — 
