80 



nant plant of the association. A few other bunch-forming species 

 may persist in this association as reHcs from the bunch-grass ; some 

 of these are Panicum perloiigiim, Andropogon scoparins, Kocleria 

 cristata, and Cypcrus schivcinitzii. The secondary species are per- 

 ennials, which persist as relics, and interstitials, which are very well 

 developed in this more open association. The species are nearly all 

 the same as those of the bunch-grass. 



The animals do not differ greatly from those of the bunch-grass. 

 The herbicolous species which live in the bunches are not so well 

 represented, but the interstitial species and those more characteristic 

 of the blowsand are very much more abundant than in the bunch- 

 grass. On the whole, the animals may be said to form a group 

 which is transitional between the animals of bunch-grass and those 

 of blowsand. The tiger-beetles, mutillids, sand-w'asps, and terricolous 

 grasshoppers are more numerous than in the bunch-grass. The 

 structure of the animal assemblage is thus seen to be parallel with 

 that of the plant assemblage. 



THE BLACK-SOIL. TRANSITION ASSOCIATION 



This association is not well represented in Illinois, for the reason 

 that in it, or even before its develbpment, the soil has reached such 

 a stage of fertility and stability that it is suitable for agriculture, and 

 only the more open associations have been allowed to remain in a 

 natural state. This stage is a relative or temporary climax in that 

 it marks the end of the sand series. It probably connects the sand 

 prairie to the prairie-grass or black-soil prairie formation of the 

 eastern part of the province, and doubtless many relics of an as- 

 sociation very much like it may be found in the tension zone between 

 the sand-hills and the prairie-grass regions. The normal tendency is 

 for the most adva<nced stage of the sand prairie to develop slowly 

 into a stage of the black-soil prairie. Under natural conditions this 

 development would rarely occur in the Havana region, for invasion 

 by the forest would be much too rapid for the succession between 

 the two prairie fonnations to be completed. Thus in the Havana 

 region we find much of the area forested, but no development of 

 mesophytic black-soil prairie. The bunch-grass has reached its most 

 advanced stage in places near the Devil's Neck, in places east of sev- 

 eral forested dune areas, and particularly in the eastern border of the 

 sand-plain. It is probable that some such vegetation covered the drier 

 parts of the sandy loam flats. Part of the growth is dominated by 

 Andropogon fiircatiis Muhl. Panicum pcrlonguni Nash marks meso- 



