86 Rhodora [May 
plants of a very different region. As the ancient river system gradu- 
ally became obliterated owing to the elevation of the land to the south 
and west, the species composing the lowland forests would one by one 
become extinct and give place to highland or xerophytie species. 
Through the vicissitudes of this changing order a form of Crataegus 
viridis was in some manner able to maintain itself, as is testified by its 
abundance at the present time on the limestone bills of southwest 
Missouri and the region to the southwestward. 
Our present knowledge regarding the origin of species is, of course, 
not sufficient to enable us to do more than conjecture as to how this 
came about. Possibly a fortuitous variety or type happened to be 
developed in this region that was better adapted to the new conditions 
and was thus able to withstand the increasing dryness, so that, while 
the species became for the most part extinct in the upper part of the 
ancient river course, this particular stock was entirely isolated from 
the parent colony and became the progenitor of the forms of Crataegus 
viridis now found occupying the regions of comparatively high alti- 
tude in the southwest, comprising the Western Ozark Colony. 
If I have not added any new species to the genus Crataegus in this 
paper, I have at least shown that the V?rides may have not come up 
the Mississippi Valley, as has generally been supposed, but have 
probably drifted down this Valley from the great Upper Mississippi 
Colony at Hannibal, Missouri and Quincy, Illinois. 
COURTNEY, MISSOURI. 
VIOLA RENIFOLIA AND V. BRAINERDII. 
M. L. FERNALD. 
Botanists who have collected extensively in the Northern States 
and Canada are familiar with the fact that Viola renifolia often 
appears in two quite different forms: the true V. renifolia as described 
by Gray, with both sides of the leaves “conspicuously beset with 
pale, soft and tender, lax hairs”;! and another extreme with the 
upper leaf-surfaces quite glabrous from the first or in anthesis with 
! Gray, Proc. Am. Acad., viii. 288 (1870). 
