a ee oe ce 
1903] FLORA OF NORTH CAROLINA 255 
8. Following the glacial period the modification of the plants 
left in the several widely removed continental areas, eastern 
North America and eastern Asia, became accentuated, as time 
elapsed, until the similarities which are marked in the plants of 
preglacial times became less well defined and the differences evi- 
dent in the two floras become the feature of recent times. 
g. These facts argue for a great antiquity of the flora of the 
mountains of western North Caroliua. The presence of so many 
peculiar types of plants, not found elsewhere in America and 
having their closest relatives in eastern Asia, makes it more cer- 
tain that groups, now broken up and detached, were once con- 
tinuous, and that fragmentary groups and isolated forms are but 
the relics of widespread types, which have been preserved in a 
few localities where the physical conditions were especially favor- 
able, or where organic competition was less severe. 
This important principle is evidenced on every hand as a 
botanist travels through western North Carolina. The large size 
of the trees, the close commingling in a dense forest of a great 
variety of species, the graded-down appearance of the land sur- 
face, and the rounded contour of the mountains, all impress the 
fact upon him that the country through which he travels has 
been subjected through long ages to the continued action of 
climatic forces which have carved the land into its present form 
and influenced the character of the vegetal covering. This 
impression is gréatly heightened, if the following nine criteria 
for determining the centers of dispersal are applied to the study 
of the region in question :* 
- Location of greatest differentiation of type. 
Location of dominance or great abundance of individuals. 
Location of synthetic or closely related forms. 
Location of maximum size of individuals. 
Location of greatest productiveness and its relative stability. 
Continuity and convergence of lines of dispersal. 
Location of least dependence upon a restricted habitat. 
. Continuity and directness of individual variations, or modi- 
_— 
SPI An wd 
* ADAMs, Cuas. C., Southeastern United States as a center of geographical dis- 
. tribution of fauna and flora. Biological Bulletin 3 : 122. 
