VI PREFACE 



The key to genera includes all the genera found grow- 

 ing wild or in common cultivation in the United States. 

 More complete descriptions of the more important genera 

 are added under each tribe. For use as a reference work 

 it would have been desirable to give full descriptions of 

 each genus. But again the author's course was modified 

 by didactic requirements. It is unnecessary for the 

 student to acquire information on the unimportant genera. 



The nomenclature followed is that of the American 

 Code. Synonjnns are introduced whenever a species or 

 genus has been commonly known under another name. 



After careful consideration, the English system is 

 used for all measurements except the small fractions of 

 an inch. But for the smaller measurements the milli- 

 meter is adopted as the unit. The English system is as 

 yet more familiar than the metric for the larger measure- 

 ments. The small fractions of an inch however are incon- 

 venient. The line might be used but is unfamiliar and is 

 too large a unit. The millimeter meets the requirements 

 as to convenience and size of unit, and is sufficiently 

 familiar to botanical students. 



The habit dra\\angs have been made by Mrs. Mary 

 Wright Gill, the detailed drawings of the spikelet by Mrs. 



Agnes Chase. 



A. S. HITCHCOCK. 

 Washington, D. C. 

 May 12, 1914. 



