6 American Midland Naturalist Monograph No. 7 



of trees and shrubs, including Pinus strobus, Taxus canadensis, and 

 Betula papyrijera, as well as a number of herbaceous plants. 



MISSISSIPPI border 



The dry western-exposed bluffs of the Mississippi River and of the 

 lower Illinois River have intermittent areas of grassland vegetation 

 containing western prairie species. Sand-prairies are present in the 

 Hancock and Oquawka areas. In a few places sand has been carried 

 by the wind from the river valley to the uplands. Along the northern 

 and central river bluffs the terrain has been deeply eroded, with result- 

 ant interruptions of the mantle of loess, and are thus at present not 

 continuously forested. The American beech. Fagus grandifolia, and 

 the tulip tree, Liriodcndron tulipifera, extend northward to Randolph 

 and Jackson counties. The common trees of the northern part of the 

 river bottoms of the Mississippi River are Acer saccharinum, Ulmus 

 americana, Betula nigra, Quercus palnstris, and Fraxinus aniericana. 

 In the southern part of this area Liqnidavibar styraciflua and Quercus 

 lyrata are common. 



SOUTHERN DIVISION 



The Southern Division is the area of oldest Illinoian Drift. Later 

 depositions of loess with subsequent weathering have complicated the 

 soil profiles. With the exception of the bottomlands, which have a 

 vegetation similar to that of the alluvial soils of the Mississippi Border, 

 the soils throughout the Southern Division are generally poor for plant 

 growth on account of their fine texture and impervious subsoil. Thus 

 they prevent good drainage and aeration, with the result that there is 

 too much water in spring and early summer, and too little in late 

 summer. The principal upland species of woody plants are Quercus 

 palustris, Q. imbricaria, Q. stellata, and Gleditsia triacanthos. Sassafras 

 albidurn and Diospyros virginiana are of not infrequent occurrence. 



WABASH BORDER 



This division includes the bottomlands and bluffs of the Wabash 

 and Ohio rivers, as well as the adjoining upland areas. A great variety 

 of species of ligneous plants is to be found in the forested areas, includ- 

 ing Celtis laevigata, Acer saccharum, Tilia americana, Nyssa aquatica, 

 and Liriodcndron tulipifera. Three species of oak, Quercus falcata, Q. 

 prinus, and Q. shumardii, as well as Catalpa speciosa, are characteristic 

 species of this part of the state. The sweet gum, Liquidambar styraci- 

 flua, extends northward to Crawford County, and the mistletoe, Pho- 

 radendron flavescens, parasitic principally on elm and other bottom- 

 land trees, is known to occur as far north as Lawrence and Crawford 

 counties. This bottomland vegetation extends many miles up the trib- 

 utaries of the Wabash River. 



OZARK HILLS 



The Ozark Ridge of southern Illinois is the most conspicuous topo- 



