124 
ILLINOIS ACADEMY OF SCIENCE 
differs considerably in its distribution in relation to the grow- 
ing season. 
Both habitats have been subject to fires and it seems pos- 
sible that fire may be a factor affecting to some extent at 
least the development and maintenance of grassland condi- 
tions. The arguments for its effectiveness in Illinois need 
not be discussed here and it may only be said that in the 
Rocky Mountains near the valley which was the site of these 
observations, where there had been repeated fires, the develop- 
ment of tree seedlings, seemed to be a slow and difficult 
matter. 
THE PLANT SUCCESSIONS 
In comparing the character and order of the development 
of the vegetation of the two grasslands the writer will limit 
himself to that portion of the Illinois prairie with which he is 
most familiar, that is, to its occurrence in the Chicago region 
and will also omit all but the necessary facts regarding this 
vegetation since they are already available in the reports of 
Cowles", Harvey and others. It will be necessary, however, 
to give rather more details regarding the Colorado mountain 
grasslands. 
In both there is a well marked hydrarch succession of as- 
sociations proceeding, in the Chicago region, from filling of 
the shallow lakes which followed the recession of the glacial 
Lake Chicago and which still persist in the form of larger and 
smaller bodies of water of which Calumet and Wolf lakes 
are examples. Very similar shallow lakes are found in Boul- 
der Park as exemplified by Park Lake. The culmination of 
these successions is, in both regions, a rather mesophytic grass- 
land that may very conveniently be designated prairie-meadow 
to distinguish it from the other associations of the series. Our 
present knowledge seems to point to this as the only manner 
of origin of the prairies of the Chicago region and as the usual 
course of development of most of the grasslands of Illinois, 
but in the Colorado mountain parks there is also a xerarch 
succession leading from the bare glacial gravels in a well 
marked series of associations slowly culminating in the same 
or a similar more mesophytic prairie-meadow. 
THE HYDRARCH SUCCESSION 
In the mountain parks of Colorado small shallow lakes are 
not uncommon, some being due to "kettle hole" origin at the 
time of the recession of the glaciers. Two of these, known 
