Jones: Flora of Illinois 5 



plant pathology, agriculture, etc. The biotic divisions now recognized are 

 as follows: 



Grand Prairie Division Southern Division 



Western Division Wabash Border 



Jo Daviess Hills Ozark Hills 



Mississippi Border Tertiary Division 



GRAND PRAIRIE DIVISION 



The term is applied to the eastern portion of Illinois, and includes all the 

 area of recent or Wisconsin glaciation which is for the most part treeless. This 

 area has the youngest soils of the state, in which leaching of dissolved mate- 

 rials has not progressed to any great extent. Characteristic prairie-plants, 

 including Silphmm terebinthinaceum, Eryngium yuccifolium, Sorghastruni 

 nutans, Andropogon jiircatus, and Sporobolus heterolepis, are frequent in 

 these areas of black prairie soil. The morainal country of Lake and McHenry 

 counties is hilly, and was formerly extensively forested. Small tracts of timber 

 still remain. Quercus macrocarpa is one of the conspicuous trees. Tilia ameri- 

 cana and Quercus borealis are frequent in drier habitats. Many of the lower 

 areas are occupied by marshes, bogs, and lakes, and in these places colonies of 

 Larix laricina are to be found. 



The counties near Lake Michigan contain a number of northern species, 

 including Larix laricina, Pinus banks'^ina, Scheuchzeria americana, Carex 

 aurea, Eriophorum angustijolium, Betula pumila, Ribes bhtellum, Shepherdia 

 canadensis, Cornus canadensis, Andromeda glaucophylla, and Chamaedaphne 

 calyculata. The beach area of Lake Michigan has numerous sand-ridges and 

 dunes, with intervening sand-prairies and sloughs. Several species are peculiar 

 to this area, such as: Juniperus canadensis, J. horizontalis , Ammophda brevi- 

 ligulata, Calamovdja longifolia, Salix cidenophylla, Cakde edentula, Potentilla 

 anserina, Prunus pumila, Lathyrus maritimus , Chamaesyce polygonifolia, Arc- 

 tostaphylos uva-ursi, and Artemisia caudata. 



WESTERN DIVISION 



This division includes most of the western part of Illinois. Much of the 

 area is covered by relatively old glacial drift (Illinoian) with recent deposits 

 of loess. These prairie areas contain several xerophytic western species, includ- 

 ing Bouteloua gracilis, Stylisma pickeringii, Lesquerella argentea, Amorpha 

 canescens, Opuntia rafnesquit, and Synthyris bullii. Areas of lower elevation 

 include prairie sloughs. Southwest of the Grand Prairie, and west of the Illi- 

 nois River, more than half the area is occupied by forest, and only a few flat 

 upland prairies of fair size, such as the Bucknell and Carihipe prairies occur. 

 This condition has been brought about by the extensive dissection of the 

 country near the larger rivers. 



JO DAVIESS HILLS 



The Driftless Area in Jo Daviess County has served as a refuge for pre- 

 glacial plants. At the present time there are several species of limited distribu- 



