8 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
The geographical range of a form is to be taken into consideration 
along with the morphological characters, in determining the taxonomic 
standing of a given group. A group distinguished by small differ- 
ences in morphological characters may be assigned subspecific or 
even specific rank when the differences are supported by a distinct 
or at least a different geographical range. Groups that are not 
sufficiently distinct to be assigned subspecific rank are mentioned 
after the general description of the species and specimens are cited as 
illustrations. In a few cases these citations are given in a formal 
manner to emphasize the distinctness of the group, in which cases the 
same specimens do not occur among those cited in the general dis- 
tribution. Usually the specimens mentioned as illustrating a par- 
ticular departure from the typical form are cited by collector and 
number or date only, and are repeated under ‘“‘ Distribution.’’ The 
locality is given in such cases only when the geographical range is of 
significance. 
GEOGRAPHICAL DISTRIBUTION. 
The species of the genus Panicum, numbering probably about five 
hundred, are found in the Tropics and warm temperate regions of both 
hemispheres. In North America the genus extends throughout the 
West Indies, Central America, Mexico, and the United States and into 
the southern part of the Dominion of Canada. The subgenus Dichan- 
thelium, which includes over one-half the species of the entire genus 
as represented in North America, is confined to the Western Hemi- 
sphere and almost to North America. The center of distribution of 
this group is the Atlantic Coastal Plain of the Southeastern States, 
whence it extends north to the eastern Canadian Provinces, west to 
the Pacific coast and British Columbia and south through Mexico and 
the West Indies to northern South America. A few species of true 
Panicum, such as P. virgatum and species of Capillaria, also extend 
over a wide range. The latter group is represented from Maine to 
British Columbia and southward into South America. The genus is 
poorly represented in the mountainous regions of the United States 
and not at allat high altitudes. Panicum thermale is found around 
hot springs in the Rocky Mountains at an altitude of 2,000 meters, but 
this is an exceptional case. The genus is poorly represented on the 
Great Plains and especially in the arid regions of the Great Basin. 
As to habitat, the species are found growing under a variety of con- 
ditions, but rarely in shady, hard-wood forests. 
CITATION OF SPECIMENS. 
The general range of all species is given, so far as indicated by 
specimens, even when this range extends beyond the limits of- 
North America. The detailed citation of specimens is given by 
