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CRIBBS—TILIA AMERICANA 



263 



into a set of varying conditions which are widely different from 

 those of its normal mesophytic environment, and affords an excel- 

 lent opportunity to investigate certain ecological and physiological 

 features which are brought under particular stress because of the 

 abrupt change in growth conditions. 



Five stations for investigation were selected on the dunes near 

 Miller, Indiana, and will be designated here as A, B, C, D, and E. 



Fig. 1. — Station A, showing Tilia on forested complex, associated with Psedcra, 

 Smilacina, Acer, and Primus. 



Studies were conducted also at station F in a mesophytic forest 

 on morainic clays in western Pennsylvania, that a comparison 

 might be had for different soil conditions. 



Station A (fig. 1) is located on an established dune complex 

 which has advanced to a state of mesophytism in regard to both 

 the tree and herbaceous vegetation. It is well sheltered from the 

 strong lake winds, and is not exposed to the intense light and the 

 accompanying high temperatures of the open sand areas. 



Station A lies deeper in the complex than B (fig. 2), which is 

 situated at the base of a forested dune and is not more than 15 m. 



