81 



phytic stations. Biiphorhia corollata Linn, is more abundant than in 

 open bunch-grass ; its white flowers are in late suniuicr the most con- 

 spicuous feature of the vegetation. Animal species typical of rather 

 less sandy situations are the sub-surface millipeds, earthworms, etc., 

 of soils containing humus; Bacunculus blatchleyi Caud. (see PI. XVII 

 in Hart and Gleason '07,) Schistocerca aiiicricaua Drury, Melano- 

 pliis fcmiir-nibrnm De G., M. diifercntialis Uhl., M. biTittatus femo- 

 rafiis Burm. ; Cyanospiza cyanca Linn, (indigo bunting), and As- 

 tnujaliiiiis trisfis Linn, (goldfinch). Even the most advanced stage 

 of sand prairie is much less mesophytic than is the typical black-soil 

 prairie as seen in northeastern Illinois, and many characteristic species 

 of the latter growth are absent. 



During a recent visit to the sand prairie (August, 1913) indica- 

 tions were found of development of black-soil prairie from the swamp 

 prairie of w^et parts of the sandy loam flats. The peculiar umbellifer 

 Eryngiuin yuccifoliuui Michx., which grows in moist soils with hu- 

 mus, was found in a station eight miles south of Havana, in what 

 was the border betw'een swamp and sand prairie. Other prairie 

 mesophytes, as Pycnanihonnin pilositni Nutt., indicate prairie devel- 

 opment from w^et habitats in the sand region. 



The black-soil transition association in the Havana region is the 

 continuation and culmination of the processes resulting from the 

 dominance of the vegetation over the physical environment: (i) the 

 elimination of the interstices between the bunches of grass, and with 

 these the interstitial plants and animals, thus changing the loose tuft 

 grow^th into a dense sod, (2) the gradual accumulation of humus, 

 (3) the increasing capacity of the soil for water storage, and (4) 

 the increase of atmospheric humidity. With the closing of the as- 

 sociation most of the perennials, including the cactus, would be 

 eliminated as well as the interstitials. There is then the tendency 

 towards the dominance of a few^ species of plants and animals, 

 rather than of numerous species. Without forest invasion we should 

 expect the successional series of the sand prairie of the sand ridges 

 and the successional series of the swamp prairie of the sandy loam 

 flats to converge ultimately in an advanced mesophytic stage com- 

 mon to both series. The processes of stabilization and accumulation 

 of humus which characterize the bunch-grass do not culminate in that 

 association ; there is a natural and gradual succession between the 

 sand-prairie formation and the prairie-grass formation typical of the 

 eastern part of the prairie province. 



