PREFACE. 



The four accompanying papers by Prof. A. S. Hitchcock, sys- 

 tematic agrostologist of the United States Department of Agriculture, 

 consist of revisions of four genera of the tribe Paniceae, a continuation 

 of his studies of North American grasses. 



The first two genera, Isachne and Oplismenus, are chiefly tropical, 

 although one species of Oplismenus extends into the southern United 

 States. The other two genera are widely distributed in tropical and 

 temperate regions. The genus Echinochloa includes the cosmopolitan 

 weed E. crusgalli, one form of which is cultivated in India for food and 

 occasionally in the United States for forage. The genus Chaetochloa 

 includes the common millet, of which there are many varieties, culti- 

 vated in the Old World as a grain and in the United States for forage. 



FREDERICK V. COVILLE, 



Curator of the United States National Herbarium. 



in 



