MICHIGAN ACADEMY OP SCIENCE. 
63 
nudicaulis, Pteridium aquilinum, Rubus hispidus, and Unifolium Can- 
adense, none of which are found in the lower burned places, and all of 
which are common in the tamarack society. Beyond this higher strip 
there is more of the burned area with practically the same plants that 
are found near the shore, in addition to a feAV bog plants, Yaccinium, 
Aronia, Betula, etc. 
Fire has been commonly used for the last century in clearing this 
country. In dry seasons fire, spreading from the uplands, naturally 
comes first into the margins, which are known to be the driest parts 
of a bog in a dry season. Every year many bogs are burned over, and 
the effects of a single fire may remain for many years. Since there are 
places on the margin having little or no depression, since the marginal 
depression is most marked where fires are known to have occurred, and 
since plant societies in depressions known to have been caused by 
fire are the same as the plant societies usually found in marginal zones, 
it is reasonable to think that marginal depressions and marginal plant 
societies are due largely to the destruction of the peat and the boo- 
plants by fire. 
CONCLUSIONS. 
1. Peat bogs are heterogeneous habitats and require detailed study. 
2. Depth of water is a primary factor in the distribution of the 
plant societies in a bog. 
3. Plant succession in older parts of this bog is brought about 
largely by fires. 
4. The replacing of tamarack forests by blueberry swamps is due to 
clearing. 
University of Michigan. 
