
84 BOTANICAL GAZETTE | FEBRUARY 
relationship between this and other classifications. Warming’s 
classification, based on the water relations, at two points agrees 
with the physiographic theory, viz., in the treatment of swamps 
and dunes. Each of these is treated from the standpoint of the 
order of succession as revealed by zonal distribution, though in the 
case of the dunes this order is not one of decreasing or increas- 
ing water content. Alb. Nilsson and Meigen (see above), and 
for that matter many other authors, have studied various plant 
societies from the standpoint of their order of succession, but so 
far as the author is aware no previous attempt has been made to 
establish a comprehensive theory on this basis. Graebner’s 
classification (see above) has several points in common with 
the physiographic theory, especially as it relates heaths with 
moors. In this connection it will be of interest to refer toa 
paper by J. B. Woodworth"? which indicates a fertile line of 
research that is but now being taken up by biologists. He 
shows how the base-leveling processes must influence the evolu- 
tion of species, since these processes constantly erect new and 
destroy old barriers, and hence cause isolation in the one case 
and intermingling of species in the other. Woodworth gives a 
number of instances of the influence of base leveling upon ani- 
mal life, and he refers, although but slightly, to the changes 
which must take place in the plant life as regions are uplifted or 
approach base level. It seems surprising that such a great field 
of study has been neglected until now. C.C. Adams, in a paper 
as yet unpublished, and C. T. Simpson * have recently given spe- 
cial cases of the interrelations between physiographic changes 
and animal distribution. 
The general principles of the physiographic theory have 
been developed as a result of studies in various sections of the 
country. Since 1898, when the author first began to work along 
these physiographic lines, the main thought has been to subject 
*7 WoopworTH, J. B.: ss Song between base-leveling and organic evolu- 
tion. Am. Geol. 14 : 209-235. 
%8StmpPson, C. T.: On the cee of the Unionidae regarding the former 
course of the Tennessee and other Southern rivers. Science N. S. 12:133-136- 
1900. 



