sively developed near Miller, Ind., but is common throughout the entire 

 dune region of Indiana and southern Michigan. 



6. The mesophytic oak forest association. — Upon the sand dunes 

 this gradually develops from the preceding by the coming in of other 

 and more mesophytic tree species, notably such oaks as Q. alba and 

 Q. rubra. It usually begins in sheltered depressions where the under- 

 growth is often very completely mesophytic before a marked change has 

 taken place in the tree vegetation. 



Upon morainic uplands this association differs but little from that 

 found upon the dunes except for the presence of the hickories and the 

 frequent occurrence of the bur oak, Q. macrocarpa. Depressions in clay^ 

 upland within this forest are often characterized by the presence of the 

 swamp white oak, Q. bicolor, or by the pin oak, Q. palustris. Corylus 

 americana and Cornus paniculata are often the most abundant shrubs 

 of the oak uplands. 



Oak forests of this type are to be seen upon the sand dunes at Bridg- 

 man and Sawyer, Mich., and in less perfect development at Dune Park 

 and Furnessville, Ind. The uplands at Smith, Ind., at Glencoe, Lake 

 Bluff, Palos Park, New Lenox, and Starved Rock Park, 111., show develop- 

 ments of oak-hickory forest of the same general type but with certain 

 minor differences of detail. 



7. The climax mesophytic forest. — This occurs, not only upon the 

 sand dunes and the morainic uplands, but also upon all soils throughout 

 the northeastern United States and the adjacent parts of Canada. It 

 is dominated in this region by the beech and sugar maple, which often 

 form more than 80 per cent of the tree growth. The hemlock is absent 

 from the uplands of the Chicago region, but is seen upon the adjacent 

 sand dunes of Michigan and in many other localities to the east and 

 north. Perhaps the most conspicuous difference between this associa- 

 tion as it occurs upon a clay upland and the corresponding forest upon: 

 adjacent sand dunes is the greater richness of the fern flora in the former 

 locality. 



The evaporating power of the air in the lower strata of the forest 

 is very low when compared with that of other associations, and at the 

 same time the soil moisture remains constantly well above the wilting 

 coefficient. 



This forest is to be seen upon the sand dunes at Sawyer, Mich., and. 

 upon the uplands at Three Oaks, Mich., Smith and Otis, Ind. 



8. Sandy swamp associations. — From the nature of the recent 

 geologic history of the region a series of old lagoons has been included 

 in the dune area, and these now exist either as small shallow lakes or 



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