A BIOLOGICAL STUDY 



OP 



POLYPODimjI POLYPODIOIDES 

 (Resui^otion Fern) 



AS 



M AIR PU^IT IN MISSISSIPPI 



LOUIS J.PESSIN 



DISSERTATION 



Submitted to the board of University- 

 Studies of the Johns Hopkins University in 

 conformity with the requirements for the 

 degree of Doctor of Philosophy, 



THE JOmiS HOPKINS UlTIVERSITY 

 BALTIMORE, MD. 

 June 1923. 



