PREFACE. 



The accompanying paper by A. S. Hitchcock, Systematic Agros- 

 tologist of the United States Department of Agriculture, and Agnes 

 Chase, Assistant Agrostologist, is supplemental to a revision of the 

 genus Panicum published by the same authors in volume 15 of the 

 Contributions under the title of ' ' The North American Species of 

 Panicum." As stated in the preface to that paper, it was impossible 

 at that time to offer a satisfactory treatment of the tropical species. 

 Since then much additional material, including collections made by 

 the authors, has been accumulated. The present paper includes the 

 results of the study of these collections and presents a fairly detailed 

 account of the genus in tropical North America. 



There are included 116 species and 3 subspecies. Of these, 9 species 

 are described as new; 5 are South American species which were un- 

 known within the limits of the area covered; 1 is a species recently 

 described ; and 4 are species that were included in the list of synonyms 

 or of dubious species but are now considered valid. In all 19 species 

 are added, making the total for the genus Panicum in North America 

 216. Each species is accompanied by an outline map graphically 

 representing the geographical distribution within the Tropics of North 

 America. 



Frederick V. Coville, 

 Curator of the United States National Herharium. 



