102 ; FIRST BOOK OF GRASSES 



should prepare an herbarium, that is, a collection of 

 plants pressed and dried in such a way that they may 

 be mounted by gummed straps to sheets of heavy 

 paper and arranged in folders for reference. Grasses 

 so prepared keep indefinitely. A circular giving 

 " Directions for preparing herbarium specimens of 

 Grasses" (Bureau of Plant Industry Document 442, 

 1909) may be obtained without charge on request 

 to the office of the Systematic Agrostologist, Bureau 

 of Plant Industry, United States Department of 

 Agriculture, Washington, D. C. 



In studying grasses the first thing is to understand 

 the structure of the plant in hand, particularly its 

 inflorescence; the second is to learn its relationship 

 to other grasses and what name has been applied to 

 it. The latter is what is meant by " identifying" or 

 " determining" a plant. Practically all the grasses 

 of the United States are described in one or more 

 manuals of botany or state floras. Most of these 

 manuals give "keys" to genera and species. [The 

 word key is used figuratively an instrument by 

 means of which a way is opened.] A key is an ar- 

 rangement of contrasting characters by which, 

 choosing one and rejecting the other, the student is 

 led to the name which applies to the plant in hand. 

 For example, take Figs. 23, 27, 45, 48, 65, and 76, 

 and trace them through the following key, read- 

 ing both of the lines having like indention, these 

 giving the contrasting characters from which to 

 choose. 



