18 BIG SPRING PRAIRIE. 
side-walks in the vicinity of the University of Chicago. 
As another instance of this difference of habit, may be 
mentioned Celtis occidentalis which, in Wyandot 
County, Ohio, occurs chiefly on ridges or bluffs, while in 
Illinois itis found only on the flood-plains of streams, as 
on the flood-plain of the Des Plaines at Riverside. A 
slight decrease in atmospheric humidity between two 
places is often sufficient to limit to very narrow boun- 
daries the habitat of certain species; which inthe more 
favorable localities have a wider range. 
Other common herbaceous plants of the Ridge 
roadsides are Melilotus alba Desv. (White Melilot): 
Plantago lanceolata lL. (Ribgrass); Poa compessa L 
(Wire-grass); Euphorbia (several species); Lithosper- 
mum arvense L, (Corn Gromwell, Wheat-thief); Trios- 
teum perfoliatum L (Horse-Gentian); Solidago (various 
species); Aster (various species); Achillea millefolium 
L, (Yarrow); Bidens and Carduns (several species). 
Polygala senega L, (Seneca Snakeroot) is rarely 
found on the ridges, and is one of the witnesses of 
former plant societies. 
The most characteristic weed of wheat-fields is 
Lithospermum arvense (Corn Gromwell. Wheat thief), 
while Ambrosia (Ragweed), Amarantus (Pigweed) and 
Chenopodium (Lambs-quarters) are also quite common. 
The region adjoining the prairie on the north and 
west was covered with a typical mesophytic forest 
formation of the Maple, Basswood, Beech type, with 
its characteristic shrubs and herbs. 
2. Past CONDITION OF THE PRAIRIE-HISTORICAL 
FACTOR. 
On Sept. 17, 1818, a treaty was agreed upon be- 
tween the U. S. Government and the Wyandot In- 
dians. One of the articles of this treaty reads as 
follows: ‘That there shall be reserved for the use of 
