256 BOTANICAL GAZETTE [OCTOBER 
fications radiating from the center of origin along the highways 
of dispersal. 
g. Direction indicated by biogeographic affinities. 
EDAPHIC FACTORS DETERMINING THE CHARACTER OF THE FLORA 
VESTERN NORTH CAROLINA 
The soils of the higher mountains are rather fine and even- 
grained loams, gray or red in color, or black from organic ingre- 
dients; the loamy and generally stiffer subsoils are red or gray. 
Over the larger part of the area they are derived from the 
decomposition, 2” s¢tu, of gneiss or gneissic schists, and are suffi- 
ciently deep for tree growth, particularly along the lower slopes. 
In portions of the region the soil derived from slates, quartzite, 
and metamorphosed sandstones are shallower, thinner, and not 
so favorable to tree growth.” Soil, according to the definition 
of Professor Dokouchayev, a Russian investigator, is the super- 
ficial horizon of rocks in which the general processes and phe- 
nomena of weathering, transportation of particles, etc., combine 
with the biologic processes due to the influence of plants (lichens 
and alpine plants), animals, and micro-organisms, such as nitri- 
fying bacteria.?3 A forest soil, such as we find in western North 
Carolina, is an expression, therefore, not only of the physico- 
geographic, geographic, and geophysic forces which have been 
brought to bear in its formation, but also of the geobiologic 
forces which have been at play. A study of any soil cannot fail 
to reveal many peculiarities of the vegetation that covers it, but 
it also throws a flood of light upon the succession of floras which 
may have flourished at any particular time in a given region. 
To elucidate: the soils of a given territory are influenced by the 
life-activities (instance the Leguminosae) and the dead remains 
of plants and other organisms (peat beds, humic compounds, 
animal manures, guano, etc.). The soil also influences the 
*PincHor and AsHE, Timber trees and forests of North Carolina. N. C. Geol. 
Surv. Bull. 6: 220. 1897. 
73 SIBIRTZEV, N., Genetic ee of soils. Zapiski Novo-Alexand. Inst. 
Selsk. Khoz. Lyesov. Memoi the Institute of Agriculture and Forestry at Novo 
Alexandria, Government of Labia 97: 1-23. 1895. Jbid., 113: 1-4. 1898. Experiment 
Station Rect #22705. 
