420 BOTANICAL GAZETTE [ DECEMBER 



when conifers are absent, they show no order of succession to 

 the forest societies. This is to be explained on the basis of the 

 migrations forced upon all boreal societies during glacial times. 



6. The absence of conifers in the Ohio basin probably indi- 

 cates the dominance of broad leaved forms there during glacial 

 times. 



Local lake and bog studies seem to indicate that : 



1. Present bog habitats are continuations of similar habitats 

 which existed in early postglacial times, when tundra conditions 

 and tundra vegetation were dominant. 



2. The temperature phenomena of undrained depressions, 

 containing deposits of peat, are favorable to the preservation of 

 these types. 



3. The "drained swamp" and "undrained swamp" classifi- 

 cation will not hold over any great area. Undrained and drained 

 depressions are both favorable to the development of the com- 

 mon swamp plants. 



4. The bog societies are composed of boreal species and, in 

 so far as the area of Ohio, Indiana, and southern Michigan is 

 concerned, must be considered as relicts of former climatic con- 

 ditions. The swamp societies, made up of more southerly forms, 

 must be considered as the normal hydrophytic vegetation of the 

 present climatic conditions. 



The above results are put forth preliminary to a more detailed 

 account to be published later. It is hoped that by this publica- 

 tion the author may be enabled to secure further data as to bog 

 societies in other localities. 



UNIVERSITY OF MICHIGAN. 



