244 : BOTANICAL GAZETTE [OCTOBER 
only by a few groups of hills where the highest mountains now 
stand. After the processes of base leveling were nearly com- 
pleted, that is, toward the close of the Cretaceous period, the 
region was again uplifted, but unequally, so that at the same 
time its surface was warped. The streams had become sluggish, 
but the effect of the uplift was to stimulate them to renewed 
activity,3 so that they began cutting upon the last-formed pene- 
plain, a process in which they are still engaged. 
PHYSIOGRAPHIC CHANGES INFLUENCING THE DISTRIBUTION OF 
PLANTS. 
Constant change must have taken place in the flora, through 
the physiographic shifts in the continent, which have been 
described as taking place in the region of the southern Appa- 
lachians. New species were appearing by the process of muta- 
tion. Other species were crowded for room by the change of 
level and the wearing away of strata to which they had adapted 
themselves, for “if we suppose that the earlier Mesozoic uplands 
were the seat of the existing dicotyledons, then by the lowering 
of the surface by gradual consumption of the interstream areas, 
these forms must have been brought into conflict with the 
ancient flora of the lowlands and thereby forced into a contest 
for supremacy.”* These changes in the physical condition of 
whole areas produced coincident changes in the constituent 
plants of the several ecologic regions. Xerophytes were replaced 
by mesophytes; mesophytes, by the wearing away of the soil 
and the formation of cliffs by xerophytes. Hydrophytes 
replaced mesophytes when an area became too wet for the ten- 
ancy of ordinary plants. Mesophytes replaced hydrophytes, as 
a lake area was robbed of its water by some newly encroaching 
stream. All of these changes were represented in the mountain 
region of North Carolina, and the plants involved in the readjust- 
ment to altered conditions were Cretaceous or Tertiary plants. 
With the development of the Cumberland peneplain, the forest 
covering, if one existed at that time (and we have no reason for 
3 HaYEs, The southern Appalachians, Joc. cit. 330. 
*WoopwortH, J. B., The relation between base leveling and organic evolution- 
The American Geologist 14: 231. 
