ACKNOWLEDGMENTS 
I wish to acknowledge, first of all, my indebtedness to Professor G. L. 
Houser and Dr. Frank A. Stromsten, of the Department of Animal Biology 
of the University of Iowa, for their excellent criticism and helpful sugges- 
tions during the preparation of this paper. Thanks are also due to Professor 
B. Shimek, of the Department of Botany, not only for his many helpful 
suggestions but for the use of unpublished data which he has prepared, 
particularly on the original distribution of forests in Johnson County. I 
wish also to thank Mr. H. M. Trusler for his reliable clerical work and 
assistance in the preparation of the maps. D, MB, 
