

Igor | GENETIC DEVELOPMENT OF FORESTS 325 
of oaks and hickories. Such clay hills in northern Michigan are 
usually covered with the climax forest. 
Again, as one approaches the semi-arid regions of the West, 
he will observe that the forest growth on the hills becomes less 
and less mesophytic until finally it gives way altogether to the 
prairie society. At the same time, the river bottom forests also 
become less mesophytic and more restricted to the banks of the 
streams. Ultimately, they, too, in the region of the great plains 
pass from existence and the prairie reaches to the very margin of 
the drainage lines. The writer has made some studies at vari- 
ous places in Kansas in reference to these points, and it is his 
intention to discuss them in full in a future paper on the eco- 
logical relations of prairie and forest. 
THE UNIVERSITY OF CHICAGO. 
