418 BOTANICAL GAZETTE | DECEMBER 
raiso moraine. When this basin was formed the area occupied 
by the other bogs was still covered by the waters of Lake Chi- 
cago (now Michigan). At the present time new bog areas are 
being continually added by the interference of the moving dunes 
with drainage lines. And these new areas frequently contain a 
number of the bog plants. This, however, does not invalidate 
the explanation here suggested. The bog habitat has been con- 
tinuous since early postglacial times; only its position and 
extent have been variable. 
This same observation holds in the case of certain lakes 
which have long supported a growth of the bog plants at some 
part of their shore line. By recent gradual changes of level, or 
by the development of a floating sedge and cassandra zone, these 
areas have been greatly enlarged in recent times. Usually, how- 
ever, such formations are partially made up of swamp species. 
It is a well-known fact that in many localities where the bog 
societies formerly existed, they have partially or entirely disap- 
peared. Since the settlement of this region, extensive bog areas 
have been cleared and drained. Fires have aided in the destruc- 
tion of the tamaracks, and in many places the sudden lowering 
of the water level due to ditching has resulted in the killing of a 
large part of the original bog flora. 
In this connection it is to be noted that the partial clearing 
or burning of a swamp area opens up a new territory for occupa- 
tion, either by the bog plants or the swamp plants. The pres- 
ervation of the underground stems of many of the bog species 
makes their chances more favorable for capturing the area in 
question. But there are many areas to the west of Ann Arbor 
which show that these bog plants cannot compete with the 
swamp plants in the occupancy of new territory, even though the 
bog plants be in complete possession previous to the clearing. 
We may say that the chances of capturing newly exposed land 
areas at the present time are all in favor of the swamp plants, 
largely because of their greater production of seeds, more ade- 
quate means for seed dispersal and better adaptations to present 
climatic conditions. In early postglacial times, however, the 
conditions were far different. The swamp plants had been 
