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. 
