57 



i^LBSTRi^^CTS OF PAPERS. 



BIOTIC ZONES AND DISTRICTS IN ILLINOIS. 



Charles A. IL\rt. 



Temperature a? a universal factor causes differences in the 

 biota according to latitude, modified to some extent by elevation 

 above sea-level, thus permitting the delimiting of life zones. 

 In the United States the three principal zones in current ac- 

 ceptation are all represented in Illinois. Zones are limited ac- 

 cording to distribution of characteristic species, and many species 

 of each zone range into the borders of those adjacent to it. 

 The ranging of Lower Austral and Transition species a consider- 

 able distance into Illinois should not be used as an argument for 

 extending the boundaries of these zones over Illinois to such a 

 distance as to unduly narrow the intervening Upper Austral 

 zone, as some investigators have done in adjacent states. 



Within the Upper Austral zone in Illinois, variations of soil, 

 vegetal covering, and climatic conditions are definitely enough 

 marked to permit the division of this area into a number of biotic 

 districts; and these, together with the adjoining zones, give the 

 following series from north to south : 



I, Transition zone. Small area at northeast, including a large 

 part of the Chicago area. 



