551 
bunch-grass association. Invasion may be affected by a single species 
or by two or more species in common. The most important of these 
pioneers observed by the writer are Panicum pseudopubescens, Paspalum 
setaceum, Sporobolus cryptandrus, Leptoloma cognatum, Carex Muhlen- 
bergii, and Cyperus Schweinitzii. On the deposit associations Panicum 
virgatum may serve as the starting point of the bunch-grass association. 
The pioneer bunch-grass association may be dominated by a single 
species or by a mixture of several species. The most important of the 
grasses in addition to those listed above are Bouteloua hirsuta, B. curti- 
pendula, Eragrostis pectinacea, Koeleria cristata, Stipa spartea, and 
Andropogon scoparius, all of which may occur as local dominants. With 
decrease in xerophytism the pioneer bunch-grasses are replaced by 
Andropogon scoparius or a mixed grass association in which both species 
of Andropogon and sometimes Sporobolus heterolepis are the prominent 
members. Sorghastrum nutans and Panicum Scribnerianum also tn- 
crease in abundance in these associations. At first the secondary species 
are largely relics of the former bunch-grass association, but in the later 
stages these are largely crowded out by Andropogon and partly replaced 
by secondary species common to the Andropogon prairies elsewhere in 
the state. In the most mesophytic stage of the Andropogon scoparius 
association the open tuft-like growth characteristic of the pioneer bunch- 
grass association is replaced by a close sod (Plate LXXIV). These 
associations are not abundant today and were found only on low dunes, 
in depressions between dunes, and on railway rights-of-way where they 
had been least disturbed by agricultural practices. 
The most mesophytic areas of the sand are dominated by Andropo- 
gon furcatus. _Vestal (27) reports Andropogon furcatus dominating 
parts of the “black-soil transition association” on sand which he finds has 
reached its most advanced stage in the Havana region “in places near 
Devil’s Neck, in places east of the several forested dune areas, and 
particularly at the eastern border of the sand plain”. Most of the sand 
prairies of this type have been either plowed or pastured. Plate LXXV 
shows an almost pure stand of Andropogon furcatus on a low dune some 
two miles south of Savanna. This dune is probably not more than 20 
feet above the river. One side grades off into the flood-plain, and the 
remaining three sides are bordered by small lakes. It has escaped both 
plowing and pasturing. About half of the dune is dominated by 
Andropogon furcatus, the remainder by Andropogon scoparius. A simi- 
lar area was found toward the base of a sand dune adjoining a swamp 
preserved for hay in the northern part of Bureau county. The older 
residents of this region report an abundance of tall bluestem on the low 
sand hills between the swamps, and an abundance of both tall and low 
bluestem, frequently mixed with other grasses, on the higher dunes. 
A large part of the sand area in Bureau county has been subjected 
to pasturing, and a blue-grass pasture has resulted in many cases. When 
the pioneer bunch-grass association or an early stage of the Andropogon 
