37° BOTANICAL GAZETTE [ NOVEMBER 
the discussion of the light-relationship of plants, is that many 
species which grow beneath the shade of a deciduous forest bloom 
in the early spring, and complete their most important vegetative 
and reproductive functions before the leaves of the trees above 
have tully unfolded. The boreal plants, however, which remained 
at the north during the glacial period, are an exception to this 
rule, for they owe their presence in the temperate forests and 
sphagnum bogs to the fact that they were trapped at the close 
of the glacial period by the northward-moving forest trees and 
had to adapt themselves to the changed conditions. Those 
boreal plants which did not do this were exterminated by the 
forest plants. 
The density of the forests affords some indication of the gen- 
eral character of the flora. Upon the slopes of the southern 
Alleghenies the deciduous forest attains unsurpassed richness 
and variety. On the slopes of the high mountains of North 
Carolina and Tennessee the principal trees of the Appalachian 
forests attain their greatest size, and in a ride of a few hours, cov- 
ering a rise in elevation of 4,000 to 6,000% (1220-1,525™), 
one may see growing in perfection trees of the south, such as 
the magnolias; trees of the middle states, such as the ashes, 
the oaks, the maples, the lindens; and then the birches, the 
pines, the mountain ashes, and the spruces, of the extreme 
north.”® 
Climatic and edaphic considerations—The differences in the 
character of the mountain region are not determined so largely 
by the kind of soil, or by the amount of moisture contained in it, 
as are those of the Piedmont plateau and the coastal region. 
Within short distances in the mountains are found wide varia- 
tions in elevation. A rapid lowering of the average annual 
temperature takes place with the increased elevation, and a pro- 
portional shortening of the growing season; increase in the rain- 
fall and relative humidity, and a decrease in evaporation both 
directly from the soil and through the foliage. It is noticeable 
that edaphic as well as climatic factors become more xerophytic 
*®Garden and Forest 5:155, 325; cf. PRICE, Practical forestry in the southern 
Appalachians. Yearbook U.S. Dept. Agric. 1900: 354 
