26B Gleason : UxXsolved problems of the prairies 



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treelessness of the prairies, which has been so widely discussed 

 by geologists and by a kw botanists also, is not to be found in 

 any of the present conditions, but in the accumulated effects of 

 centuries of arid climate in the southwest, from which direction 

 the plants of our prairies immigrated. 



2. The flora of the prairies of the Wisconsin glaciation in the 

 northern part of Illinois is very different from that of the Illinoisian 

 glaciation at the south, estimated to be eight times as old. Does 

 this flora at the south indicate the survival of a pre-Wisconsin 

 interglacial flora, which persisted during the Wisconsin period, or 

 an invasion of prairie species from a different direction or at a dif- 

 ferent time, or merely an adaptation to different conditions of soil, 

 temperature, or rainfall, or something else ? So far as I know, no 

 one has attempted to account for this peculiar feature of the Illi- 

 nois flora. Personally, it seems that it must in some way be 

 related to, or caused by, pre-Wisconsin conditions, although what 

 those conditions were I have no idea. Certainly, an understand- 

 ing of this question would aid in answering the first one also. 



3. The aquatic plants surrounding the sloughs and ponds of 

 the prairie were generally of broad distribution, or at least in no 

 wise typical of the prairie province. Tlie latter class of plants was 

 usually semi-xerophytic, and occurred in the uplands. What is 

 the significance of this? Does it throw any light upon the order 

 of entrance of plants, and of western plants in particular, into this 

 area? 



4. The occurrence of scattered colonies of prairie species be- 

 yond the eastern limits of the province may indicate a former more 

 extensive range of the prairie. A notable example of this is the 

 colony on Cedar Point, near Sandusky, Ohio,t probably two 

 hundred miles east of their normal limits. Will it be possible by 

 careful search for such relict colonies in other places to determine 

 what was the maximum extension of the prairie ? This would aid 

 in giving a good idea of the rate of invasion of the forest. 



5. The isolated occurrence of the western plants on Cedar 



*Cf. Harvey, loc. a'L, 84. 



f Jennings, An ecological classification of the vegetation of Cedar Point. Ohio 

 Nat. 8: 291-340./. /-^^. 1908. 



See also Bonser, Ecological study of Big Spring prairie, Wyandot County, Ohio. 

 Ohio Acad. Sci. Special Paper 7. 1903. 



