140 STEVENS: PREVALENCE OF ENDOTHIA GYROSA 
Quercus are by far the most favorable places for infection of E. 
gyrosa. In the southern states climatic and cultural conditions 
combine to make such exposed roots very much more common 
than in the northern states. 
EROSION 
The difference in soil erosion alone would largely account for 
the much greater abundance of exposed roots in the south. While 
no accurate data as to the relative erosion in various parts of the 
country are at hand, a review of the literature of the subject 
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TROPICAL FORESF 
Fic. 5. Forest regions of the eastern United States. Map supplied by United 
States Forest Service. , 
_ shows clearly that in the states of Virginia, Kentucky, Tennessee, 
North and South Carolina, Alabama, Georgia, Louisiana, and 
Arkansas soil erosion is a serious problem. Davis in a recent 
review (2) of the subject calls attention to the fact that throughout 
