viii INTRODUCTION. 



page 33 must be kept in mind when using them ; for in 

 the tribes as well as in the larger genera the characters 

 given are of necessity subject to many exceptions. 



Under each genus will be found its distinguishing 

 characters not already mentioned in the keys, the num- 

 ber of species it embraces and their geographical dis- 

 tribution, also the names and uses of those species of 

 marked economic value. The somewhat extended ac- 

 count given of the Cereals and Bamboos, due to their 

 special importance, contains much of general interest. 



