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 econony and to avoid, delay in publication. 



Washington, D. C. 

 July 1950 



