84 Rhodora [May 
distinct from the southern species, and as over three hundred miles 
of forest land and prairie lie between it and the Western Ozark Colony, 
an area in which no Virides have ever been found, it is hardly probable 
that the species of the two colonies are the same. 
To me it is apparent that in some remote time the Western Ozark 
Colony, as well as the Upper Mississippi Colony, consisted of a few 
individuals, which have adapted themselves to their surroundings 
and have continued to multiply until today there are thousands of 
individuals at each colony differing more or less from each other and 
from the original members of the colony. 
Whether these forms are sufficiently distinct to be called species or 
varieties is a question which may never be settled, but I am firmly 
of the opinion that these colonies contain species more or less fixed, 
species with which I am somewhat familiar and which are as yet 
undescribed,! but which I do not wish here to describe, leaving that 
to those more capable of drawing their descriptions and determining 
their relationships. 
Having shown that the center of greatest development for Crataegus 
viridis L. is not, as has been so often stated and generally believed, 
in the Lower Mississippi or Gulf region, but rather in the Upper 
Mississippi Valley, and that in all probability this species and its 
most nearly related congeners were distributed from that center, it 
may be worth while briefly to inquire, even though it may be possible 
to do little more than speculate, as to how this distribution was effected. 
The true key to the distribution of Crataegus viridis L., as of many 
of our trees and some herbaceous plants, is probably to be sought and 
ultimately, if ever, found in the records of the flora of the later Tertiary 
period: a record, unfortunately, very imperfect and but little under- 
stood, and one which, at least so far as present day discoveries have 
gone, seems to have been almost totally effaced in the region under 
consideration. 
It has been pointed out that in Tertiary times a great inland sea or 
arm of the gulf extended far up the present valley of the Mississippi 
into what is now southeastern Missouri, occupying all of Missouri 
lying southeast of a line drawn from Cape Girardeau through White- 
water, Greenbrier, Wappapello, Poplar Bluff and Acorn, coinciding 
very nearly with the line of the St. Louis, Memphis and Southeastern 
1Since this paper was written Sargent has described in the twenty-second Annual 
Report of the Mo. Bot. Garden, four species of this group. 
