124 ILLINOIS ACADEMY OF SCIENCE 



3. Andropogon furcatus is the most abundant grass of 

 this climax prairie, and usually occupies more than 80 per 

 cent of the total area of the association which it represents. 

 This fact suggests that Andropogon furcatus is the climax 

 grass of the Illinois prairies. 



4. In their order from pioneer to climax, the most impor- 

 tant associations of the hydrarch successions are Scirpus fluvi- 

 atilis, Carex vesicaria, Spartina Michauxiana, Calamagrostis 

 canadensis, Panicum virgatum and Andropogon furcatus. 

 The most important associations of the xerarch succession on 

 sand are Panicum pseudopubescens, Andropogon scoparius 

 and Andropogon furcatus; on clay, Andropogon scoparius 

 and Andropogon furcatus. 



5. During long continued grazing the Andropogon and 

 Panicum virgatum associations are displaced by a blue grass 

 (Poa pratensis) sod. Each of the other associations is like- 

 wise displaced by more or less definite types of pasture plants. 



6. Owing to the numerous diverse types of disturbance 

 by man, the associations of prairie plants on railway rights- 

 of-way are unnatural and in certain respects do not agree with 

 those found on the undisturbed virgin areas. Relic patches 

 of these virgin associations on these rights-of-way are, how- 

 ever, still abundant enough to give a general picture of the 

 original prairies. Data collected from this point of view 

 show that most of the prairie area of the older glaciated re- 

 gions of the state had reached the Andropogon furcatus stage 

 before the coming of the plowman, while much of the prairie 

 area of the Wisconsin glaciation was dominated by Spartina 

 Michauxiana, Calamagrostis canadensis and Panicum virga- 

 tum, according to the development of the drainage condi- 

 tions. This conclusion is further substantiated by the word 

 of the older inhabitants who saw these prairies in all their 

 original grandeur. 



7. In a general way the trend of the associations on the 

 black-soil clay prairies follows the changes in the moisture 

 content of the soil as the physiography of the regions de- 

 velops. In the sand prairies transpiration, stability of the soil 

 and probably nutrition are also factors of prime importance. 



