4 American Midland Naturalist Mo?-iograph No. 7 



states. Extensive forests and grasslands formerly covered the entire 

 region. In the northeiTi part there were large prairies with tongues of 

 forest extending along the principal watercourses. At the present time, 

 although the vegetation has been greatly disturbed, the flora is still 

 rich and varied, with a large number of species of grasses, as well as 

 other herbs and ligneous plants. The more extensive forested areas 

 are chiefly in the southern counties, especially on the flood plains of 

 the principal rivers, and in the Ozark Hills. These forests are com- 

 posed almost entirely of hardwoods. Oak, hickoiy, maple, elm, and 

 ash are among the more common kinds of trees. 



Formerly one of the most remarkable features of the state of Illinois 

 was its great stretches of prairies covered with rich growth of tall 

 grasses and several himdred species of other herbaceous flowering 

 plants. The most extensive of these prairies occiured in northern and 

 central Illinois, and were interspersed with numerous swamps and 

 shallow ponds which have long since disappeared. However, the orig- 

 inal prairie has all but vanished from the Illinois landscape, and no 

 typical area of upland prairie remains for botanical study. Extensive 

 tracts of these upland prairies were swampy, but almost all have been 

 drained and their natural vegetation has since disappeared except 

 from roadsides and along the railroads. Other areas are covered chiefly 

 with sand or sandy loam, and support a flora of psammophilous species, 

 including Leptoloma cognatum, Tephrosia virginiana, H elianthemum 

 canadense, Oenothera rhomhipetata, Phlox bifida, Lithospermum 

 croceum, and Chrysopsis villosa. The principal sand-areas are in the 

 northeiTi half of the state. 



Vegetation al Divisions 



The spontaneous flora of Illinois comprises a vegetation that is 

 rather sharply diff'erentiated into prairie and forest. Each of these two 

 types of vegetation includes a number of communities or associations, 

 reflecting the transitions in temperature and rainfall, as well as the 

 topographic and edaphic conditions. On the accompanying map the 

 ecological divisions are based principally upon the broader topograph- 

 ical features, including the effects of glacial geology. The area afTected 

 by the recent (Wisconsin) glaciation is mostly treeless, and extensive 

 areas of upland prairie formerly occurred in the western division. It 

 will be noted that the botanical areas are correlated with the various 

 agricultural districts, and are thus intimately connected with various 

 phases of human geography. Moreover, it is obvious that faunal areas 

 parallel the natural botanical divisions, and thus these divisions are 

 useful to zoologists, as well as to students of the applied branches of 

 biology, including plant pathology, agriculture, etc. The biotic divi- 

 sions now recognized are as follows: 



Grand Prairie Division Southern Division 



Western Division Wabash Border 



Jo Daviess Hills Ozark Hills 



Mississippi Border Tertiary Division 



