122 ILLINOIS ACADEMY OF SCIENCE 



ance of the valley floor is not unlike that of the lake plain 

 which succeeded the ice sheet in the Chicago region and is at 

 present partly occupied by edaphic prairie. It therefore seems 

 that it would be interesting to compare the conditions which 

 have produced grasslands in these two areas, situated in rather 

 widely removed regions and differing in so many respects. It 

 may be possible that such a comparison may so stimulate in- 

 quiry that further research along this line may contribute 

 something to the general problem as to the factors that are 

 efficient in producing this type of vegetation. A full analysis 

 of the composition of the vegetation is not possible nor is it 

 either desirable or necessary, for it has already been rather 

 completely done by Ramaley 1 , Robbins 2 , and others connected 

 with the Colorado Mountain Laboratory. 



CLIMATIC CONDITIONS 



As already indicated the prairies of Illinois and the moun- 

 tain grasslands of Colorado now under consideration, differ 

 rather more than 8000 feet in altitude, and this brings a cor- 

 responding difference in temperature. The mean summer 

 temperature of Boulder Park is about 15 degrees F. lower than 

 that of the Chicago Region, only about six weeks of midsum- 

 mer are usually free from frosts and a drop in temperature 

 below the freezing point has been known to occur during al- 

 most every week of the year. There is almost no growth be- 

 fore June first, and very little after the end of August, thus 

 making a short vegetative season that almost entirely elimin- 

 ates annuals from the mountain habitat. Winter tempera- 

 tures also differ somewhat, but probably not enough to ma- 

 terially affect vegetation, at least it may be said that this 

 mountain park is no colder than many prairie regions, such 

 as those of the Dakotas. 



In humidity the two regions are probably closely compar- 

 able, although no accurate data are available from Boulder 

 Park, where, in spite of the light showers that are an almost 

 daily occurrence during a considerable portion of the sum- 

 mer, the mountain air is quite as dry as that of Illinois dur- 

 ing the summer months. The amount of precipitation in the 

 two localities is of the same order of magnitude, Illinois, 

 (about Chicago) averaging a little over 30 inches and Boulder 

 Park a little less than that amount, per annum. Curiously 

 enough snow never accumulates to any great depths nor does 

 it usually remain long in this valley, probably on account of 



