VESTAL: A BLACK-SOIL PRAIRIE STATION 361 
trum and Liatris scariosa prairie consocies has also been treated 
by Gates (I. c., pp. 300-303, pl. 39). The convergence of sand 
prairie and xerophytic prairie of other soils into less xerophytic 
prairie-grass has been described by the writer.* The more 
markedly xerophytic prairie-grass types are no longer present in 
eastern Du Page County, but may be seen in areas of older drift, 
as in Ogle County (lIllinoian glaciation), or in still drier situations, 
as loess-capped bluffs of the Mississippi River (seen at Savanna, 
Illinois) and other prairie-grass stations farther west. Develop- 
ment of mesophytic prairie, from both xerophytic and hydrophytic 
F1G. 7 
Fic, A forest border at the county line station. Andropogon furcatus 
prominent in foreground; sunflower and dogwood zones at the edge of the_forest; 
gtapevines on some of the shrubs. 
extremes, may be due to action of the vegetation itself or to phys- 
ical changes of environment. Retrogressive successions occur 
locally. Relic species from the former condition are perhaps more 
* Vestal, A.G. An associational study of Illinois sand prairie. Bull. Ill. State 
Lab. Nat. Hist. 10: 1 96. 
1913. (The black-soil transition association, p. 80.) 
The st 
atus of prairie associations in the southern beach areas of Lake Michigan. 
Jour. of Ecology. In press. (The dry prairie-grass association. 
