PREFACE. 



In the accompanying papers A. S. Hitchcock, systematic agros- 

 tologist of the United States Department of Agriculture, and Agnes 

 Chase, assistant agrostologist, have continued the record of their 

 studies upon North American grasses, presenting a revision of four of 

 the smaller genera of the tribe Paniceae. The method of treatment 

 is the same as that followed in an earlier paper entitled The North 

 American Species of Panicum (published as volume 15 of the Con- 

 tributions, 1910), of which Prof. Hitchcock and Mrs. Chase were 

 joint authors. 



The first two genera, Ichnmithus and Lasiacis, are tropical Ameri- 

 can, though one species of the former has been introduced into the 

 Philippine Islands, and one species of the latter extends into southern 

 Florida. The genus Brachiaria is found in the warmer parts of both 

 hemispheres and in America extends into the southern United States. 

 The genus Cenchrus, whose species are usually known as sandburs, 

 is widely distributed in the warm and temperate regions of both 

 hemispheres, some of the species being troublesome weeds. 



Frederick V. Coville, 

 Curator of the United States National Herbarium. 



