August, 1955 
lata, and Sorghastrum nutans. Thus, in 
50 per cent or more of the hill prairies, 
there were 25 species present. All are na- 
tives of North America except one, possi- 
bly two. Melilotus alba is Eurasian. Poa 
pratensis is generally considered European 
by many authorities, but Gleason (1952) 
states, “In most of our range introduced 
from Europe; along our n. boundary and 
in Canada it may be native.” It might 
prove difficult to determine whether IlIli- 
nois plants of this species had their origin 
in Europe or Canada. 
Species most characteristic of the hill 
prairie type are Bouteloua curtipendula, 
Psoralea tenuiflora, Petalostemum  can- 
didum, Linum sulcatum, and Lithosper- 
mum incisum. The presence of these spe- 
cies in other prairie types in Illinois is 
much lower than in hill prairie. 
Seasonal Aspect.—The Illinois hill 
prairies studied in the years covered by 
this report showed certain seasonal as- 
pects. 
In winter, the brownish color of the 
grass cover predominated. On some un- 
grazed hill prairies, tall grass stems of 
the previous growing season bent over and 
trended downslope to form a fairly com- 
plete cover over the soil. Small purplish 
rosettes of Solidago nemoralis and green 
rosettes of Senecio plattensis were evident 
between the grass clumps in some of the 
prairies. 
The prevernal aspect was mostly 
brown. In early April in some prairies, 
the small white flowers of Draba reptans 
were seen. By late April, the violet flow- 
ers of Oxalis violacea, the yellow-orange 
blossoms of Lithospermum canescens, and 
the yellowish flowers of Salix humilus and 
Rhus aromatica were evident among the 
grass bunches. 
In the vernal phase, the dominant color 
changed from brown, through brownish- 
green, to green as the grasses began their 
growth. Hedeoma hispida, with very 
small bluish blossoms, was common in the 
interspaces in many prairies. Erigeron 
strigosus, taller than the grasses during 
the vernal phase, was very conspicuous 
with its white flowers, as was also Pen- 
stemon pallidus. Tradescantia, with pur- 
ple blooms raised above the level of the 
grasses, was scattered in many prairies. 
Evers: Hity Prairies oF ILLINOIS 393 
The yellow rays of Senecio plattensis and 
Coreopsis lanceolata were conspicuous in 
some. Several grasses, Panicum scrib- 
nertianum, Poa pratensis, Festuca octo- 
flora, and Koeleria cristata, flowered at 
this time. 
In the aestival stage, the predominating 
color was green or purplish-green. Echi- 
nacea pallida, with purplish rays, was in 
bloom, and Linum sulcatum, with small 
yellow petals, began its flowering. In 
some prairies the small whitish flowers of 
Houstonia nigricans were frequent. The 
inflorescences and foliage of Psoralea 
tenuiflora gave some prairies a purplish- 
green hue, especially in early July. The 
purple-flowered Buchnera americana and 
Petalostemum purpureum and the white- 
flowered prairie-clover, P. candidum, were 
scattered in some prairies. In late June 
and early July, the green or purplish- 
green inflorescences of Bouteloua curti- 
pendula appeared. In the latter part of 
July and early August, the bronze, green, 
or purplish-green inflorescences of JAn- 
dropogon scoparius and A. gerardi were 
conspicuous. By late August, the yellow 
of Solidago nemoralis and the purple of 
Liatris aspera were evident. 
In the autumnal phase, beginning in 
September, the dominant color changed 
from green to brownish hues. The yel- 
low rays of Solidago nemoralis and the 
white or purple rays of several species of 
Aster were common. By October, very 
few plants, an occasional Solidago or a 
Houstonia, or, less often, a Spiranthes, 
were still in flower. By November the 
prairie was again dormant; the dominant 
grass cover was brown. 
VEGETATIONAL HISTORY 
AND SUCCESSION 
The vegetational history of Illinois, a 
state that is within the area of overlap 
of eastern prairie and forest, is deduced 
mainly from circumstantial evidence. The 
evidence is derived from the present flora 
and vegetation, especially from apparent 
relict colonies, from fossils in the loess, 
and from analyses of pollens and fossils in 
peat and lacustrine deposits. Deductions 
must conform not only to the facts of bot- 
any but also to the facts of meteorology 
