In a complex forest association such as found in Indiana one is confronted with interesting distribution patterns of some species. These same species may to some degree all associate in the mixed mesophytic forest association. All of them are adapted to the macroclimate but can be segregated from the climax association complex into smaller individual groups by variations of the microclimate. This is determined by physiographic conditions which may modify aerial and edaphic factors. Potzger has discussed this phenomenon as operative in distribution of sugar maple, beech and white oak. Potsger and Friesner referred to it in Quercus rubra and Q. velutina. All of these segregations are, of course, due to modifications of the macroclimate in more or less limited areas. It is quite obvious that identical soil and physiographic factors in Indiana and northern Michigan, let us say, could not involve segregation of the same genera and species with small variations in the edaphic and aerial factors because of the major selection of species by the macroclimate, or generalized climate, which is greatly different in the two locations.