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are usually characteristic of the forest. Some of these, as 

 Claytonia virginica, Erythronium alhidum, and Trillium recur- 

 vatum, are geophytes of the prevemal season, which complete 

 their annual cycle of development before midsummer, and at the 

 usual time of prairie fires are already in the resting stage. In 

 that condition they would not be injured by fires and, since their 

 methods of seed dispersal are not very efficient, they suggest 

 very strongly that their present habitat was formerly covered 

 by forest. If they were recent introductions from the forest, 

 they might be expected most abundantly near the forest, and 

 on other types of soil besides the morainal hills. However, the 

 only records of these species growing together, and the only 

 prairie records of any sort known to the writer for Erythronium 

 and Trillium, are from morainic hills at a considerable distance 

 from existing forests. 



It has already been mentioned that the hazel was a character- 

 istic plant of the forest margin, and that it was not seriously 

 injured by fire. If the forest was completely removed by fire, 

 it might be expected that the hazel would be the last forest 

 shrub to disappear. There is one record known to the writer 

 of a large hazel thicket, covering several acres at the western 

 edge of an upland forest, and several such records of scattered 

 thickets of hazel in the middle of the prairie, but always on 

 moraines. 



All three lines of evidence point to the same conclusion, and 

 it may even yet be possible to determine the migration route 

 of the morainal forests from other forests along the river systems. 



In conclusion, it seems evident that prairie fires have been the 

 deciding factor in determining the distribution of forests in the 

 Middle West. With prairie fires eliminated, the forest is naturally 

 dominant, and tends to spread over wider areas at the expense 

 of the prairie. Under the attack of prairie fires, the forests have 

 been driven back or destroyed, except in those areas where the 

 favor of morainic or fluviatile topography has enabled them to 

 resist the encroachments of the prairie. 

 University of Michigan 



