[Vol. 8 
124 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
been analyzed as far as possible with the data at hand. Certain 
theories of development depending upon range or area occupied 
have also been considered in relation to the present genus and 
evidence concerning their validity obtained. Finally, it has 
been attempted to procure definite data in regard to the distri- 
bution of Lesquerella that will serve on comparison with similar 
data procured from related genera to show any significant differ- 
ences in the types of distribution. 
The species of Lesquerella are native chiefly to the arid parts 
of western North America. Three species occur in South 
America. One of these, L. mendocina, seems to be rather widely 
distributed across northern Patagonia; another, L. montevidensis, 
has been reported from Uruguay ; and the third, L. frigida, was 
collected in the high mountains of Venezuela. In North America 
three other isolated species are found: L. arctica in Greenland 
and on the shores of arctic America, L. globosa in Kentucky 
and Tennessee, and L. Lescurii in the immediate vicinity of 
Nashville, Tennessee. The remaining forty-six species occur in 
a nearly continuous area adjacent to the Rocky Mountains from 
Canada to the southern extremity of the Mexican plateau. On 
the east this region penetrates to eastern Texas and southwestern 
Missouri, and on the west to the states that border the Pacific 
Ocean. The geographical center of this continuous zone lies 
somewhere in northern New Mexico, but the region of greatest 
specific concentration is located in central Texas not far from the 
eastern edge of this area of continuous distribution. Utah and 
southern New Mexico are also rather remarkable for the number 
of species that occur within a small area (fig. 4). 
Point of Origin.—There is much evidence for believing that 
Lesquerella originated at some point in central Texas and from 
this point as a center has spread over the large area that it now 
occupies. Other things being equal, one might suppose that 
migration would take place equally in all directions from the 
point of origin. It will be seen that the Texas region, although 
at one edge of the area of continuous distribution, is not far 
from the center of total distribution. That it is not at the exact 
center is obviously no argument against the present hypothesis. 
From purely theoretical standpoints also, the greatest number 
of species might be expected to occur in the vicinity of the point 
