.?70 



Illinois Natural Historv Sur\ev Bulletin 



Vol. 2b, Art. 5 



this study ; for their help 1 am trulv grate- 

 ful. 



Also, I wish to acknowledge here the 

 assistance given by Mr. \V. H. Phegley 

 and Air. J. J. Steibel of Prairie du 

 Rocher, both of whom are now deceased. 

 Some of the vegetation studies for this in- 

 vestigation were accomplished through 

 their kind co-operation. I wish to thank 

 Dr. G. VV. White, Department of Geol- 

 ogy> University of Illinois, and Dr. H. 

 B. Willman and Dr. G. E. Ekblaw, Illi- 

 nois State Geological Survey, for infor- 

 mation concerning the geology of hill 

 prairies; Mr. B. M. Woods, University 

 Library Map Room, for his efforts to lo- 

 cate suitable aerial photographs; Mr. 

 Julian Neill, East St. Louis, for assist- 

 ance in the stud\ of hill prairies in that 

 region; Dr. J. L. Forsherg, Dr. P. F. 

 Hoffman, Mr. J. W. Curfman, and Mr. 

 R. E. Teegardin, while members of the 

 Natural History Survey staff, for assist- 

 ance with the statistics, the hydrogen-ion 

 determinations, and the maps, diagrams, 

 and drawings; and Mr. J. S. Ayars, also 

 a Survey staff' member, for his assistance 

 with editorial problems. 



Others I wish to thank for their con- 

 tributions to this investigation are Dr. M. 

 W. Sanderson, Dr. H. H. Ross, Dr. L. 

 J. Stannard, Illinois Natural Histor\ 

 Survey; Mr. and Mrs. F. W. Evers, 

 Quincy; Mr. Ra\mond Hatcher, Mur- 

 physboro; Dr. J. W. Hall, University of 

 Minnesota; Mr. and Mrs. B. C. Trees, 

 East St. Louis; Frederick Evers, Clara 

 V. Evers, and Marilyn Briggs Ellerman, 

 Champaign ; and Miss X'irginia Frank, 

 Chicago. 



Mr. Dewey Clark, Quincy, took the 

 pictures for the frontispiece and Hg. 16. 

 Mr. W. E. Clark, Natural History Sur- 

 vey staff", took the photographs used as 

 figs. 3, 17, 18, 22, and 24. All other 

 photographs were taken by the author. 



The plant nomenclature used in this 

 study is for the most part that of Hitch- 

 cock (1950) for grasses and Fernald 

 (1950) for other plants. XV'here the no- 

 menclature in this report does not con- 

 form to that in the manual of Hitchcock 

 or that of Fernald, the manual name is 

 included in brackets in the section on the 

 flora of hill prairies. In instances in which 



a name of long standing has been changed 

 in recent manuals, the former name, in 

 brackets, also appears. Common names not 

 from the above manuals are from Deam 

 ( 1040) or Jones (1950). 



ENVIRONMENT 



The occurrence and distribution of 

 plants, and consequenth' plant communi- 

 ties, is determined largely by climate and 

 other enviromnental conditions, including 

 the soil or substratum in which they grow. 

 Some of the environmental conditions fa- 

 voring the existence of hill prairies in Illi- 

 nois are discussed in the following sec- 

 tions. 



The climate in practically any part of 

 Illinois permits growth of either prairie 

 or forest. The circumstances (aside from 

 those of accident and of history) which 

 tip the balance and thus determine the 

 details of local distribution of prairie and 

 forest are cln'elU the controls exerted by 

 topography. 



Climate 



The following information on climatic 

 conditions applies to the Mississippi River 

 valley along the western border of Illi- 

 nois, the region of the majority of hill 

 prairies observed for this report. With 

 few exceptions, the climatic data, taken 

 from Page (1949), are from weather sta- 

 tions located along the Mississippi River. 

 Exceptions are the data from the Mount 

 Carroll, Carbondale, Anna, and Green- 

 ville weather stations; these stations are, 

 respecti\ely, about 9, 11, 12, and 33 miles 

 from the nearest hill prairies. 



Temperature. — The average January 

 temperature along the western border of 

 Illinois varies from 19.6 degrees Fahren- 

 heit in northwestern Illinois (Dubuque, 

 Iowa, weather station) to 36.2 in south- 

 ern Illinois at Cairo. The average July 

 temperature is 74.6 degrees in northwest- 

 ern, 80.2 in west-central (Quincy weather 

 station I, and 79.8 in southwestern and 

 southern Illinois (St. Louis, Missouri, 

 and Carbondale, Illinois, weather sta- 

 tions). In Cairo, at the southernmost 

 weather station in Illinois, the average 

 July temperature is 79.5 degrees. The re- 



