AN ISOLATED PRAIRIE GROVE AND ITS PHYTOGEO- 
GRAPHICAL SIGNIFICANCE’ 
HENRY ALLAN GLEASON 
(WITH TWO FIGURES) 
Probably less study has been given in recent times to the rela- 
tion of prairie and forest than to any other general phytogeo- 
graphical problem in the central states. Some of the large number 
of questions still awaiting satisfactory solution were briefly stated 
in a former paper,? and in the following pages some evidence 
bearing on one of them is given and some conclusions of a more 
general nature are drawn. The present paper is not so much a 
description of modern conditions as an attempt to explain by exist- 
ing distribution certain historical features of the relation of forest 
and prairie in central Illinois. It is probable that the conclusions 
drawn from the local area apply equally well to many other por- 
tions of the eastern extension of the Prairie Province. 
Early histories and maps show that the prairies of central 
Illinois were not continuous, but occupied chiefly the higher ground 
between the drainage systems. The latter were bordered in their 
lower courses by forests, which occupied the floodplain and bluffs 
and extended out a short distance on the uplands. The sources of 
the streams were usually in the prairie, and their margins were 
occupied by prairie vegetation for the first few miles. Scattered 
about on the prairie were a few isolated groves, far removed from 
the larger bodies of forest along the water courses. These groves 
were important to the Indians and early settlers as landmarks 
and camping grounds, and at a later period formed centers from 
which the settlement of the prairie proceeded. Bur Oak Grove 
is an example of such an isolated area of forest. It is situated in 
the east-central part of Champaign County, on the east side of the 
«Contribution no. 123 from the Botanical Laboratory of the University of 
Michigan. 
2Some unsolved problems of the prairies. Bull. Torr. Bot. Club 36: 265-271- 
1909. 
Botanical Gazette, vol. 53] [38 
