Explanatory Note 



The series embodies results of investigations, usually of restricted 

 scope, intended to aid or direct management or utilisation practices and 

 as guides for administrative or legislative action. It is issued in limi- 

 ted quantities for the official use of Federal, State or cooperating Agencies 

 and in processed form for economy and to avoid delay in publication. 



Washington, D. C. 

 July, 1952 



