Explanatory Note 



The series embodies results of investigations, usually of 

 restricted scope, intended to aid or direct management or 

 utilization practices and as guides for administrative or 

 legislative action* It is issued in limited 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* 

 April 1950 



