TEHON: FIELDBOOK OF NATIVE ILLINOIS SHRUBS 9 



to time; but the lengthy descriptions accorded other species 

 have not been given. 



How to Name Shrubs. — The first purpose of a manual is 

 to assist persons in finding names for plants in which they are 

 interested. With the keys in this manual, a person without bo- 

 tanical training can, with a little time and effort, find the names 

 of shrubs utterly strange to him. 



It always has been difficult to explain how to use a botanical 

 key. This is true, perhaps, because a key provides directions 

 both for coming to a conclusion and for obtaining a set of facts 

 upon which to base the conclusion. It is puzzling to the inexperi- 

 enced user at first. However, it has this advantage: it prede- 

 termines for its user the items that must be observed and, when 

 they have been observed and properly followed through, pro- 

 vides immediately the required conclusion. The things to be 

 observed are the distinguishing characteristics every kind of 

 shrub possesses, and the conclusions drawn from them are 

 names of shrubs. 



To illustrate the manner in which a key works, we might 

 imagine that a stranger has asked what house is occupied by a 

 person living on a street with which we are very familiar, al- 

 though we cannot quite remember the house number. When we 

 give directions to the stranger for finding the house, we may 

 not say all of the following things, but our process of thought 

 may be imagined as this: "The house is not in the first four or 

 five blocks, but somewhere in the sixth, seventh or eighth block. 

 It is on the south side, not on the north side, of the street, and 

 it is a brick, not a frame, house. It has a wide porch across the 

 front, so that the door does not open immediately to the side- 

 walk, and it is moreover the only house of this general descrip- 

 tion where three small evergreens stand on each side of the 

 steps leading to the porch." 



With such a set of directions our stranger will know about 

 how far to go, which side of the street to look on, and the kind 

 of house to look for. And he will know one definite fact that 

 will enable him to recognize the house, when he comes to it, as 

 certainly as though he knew its number. 



The key for naming shrubs works on exactly the same basis, 

 except that it must include, so to speak, every house on the 

 street or, in our case, every shrub in the state; it is based simi- 

 larly on important characteristics. These characteristics are set 



