PREFACE. 
The accompanying paper, entitled The North American species of 
Panicum, by A.S. Hitchcock, Systematic Agrostologist of the United 
States Department of Agriculture, and Agnes Chase, Assistant in 
Systematic Agrostology, is the result of an exhaustive study of the 
material of this genus in the United States National Herbarium and 
in the other large herbaria of the United States. All the more impor- 
tant herbaria of Europe were visited by Mr. Hitchcock for the purpose 
of examining the type specimens of American species described by 
European authors. This opportunity is taken to acknowledge the 
many courtesies extended by the curators of the herbaria visited. 
In addition to the knowledge of the genus gained through an exami- 
nation of many thousand herbarium specimens, the authors have 
had opportunity to collect material throughout the United States 
and have observed nearly all the species of that region in their native 
habitats. Because of the lack of material and of the necessary field 
studies, it has been impossible to present the species of tropical 
America with the same degree of detail as the species of the United 
States, but it has seemed advisable to include these tropical species 
in order to bring together in one paper our present knowledge of the 
genus in North America. 
The authors describe 197 species and 8 subspecies, each of which 
is accompanied by a text figure illustrating the spikelet and fruit. 
The descriptions of species occurring within the limits of the United 
States are also accompanied by an outline map graphically represent- 
ing the geographical distribution. 
FREDERICK V. COVILLE, 
Curator of the United States National Herbarium. 
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