U. S. Dept. of Agr., Bui. 150, Office of Expt. Stations. 



Plate !. 



> 



O 

 I 



m 

 o 



o 



I 



O 

 o 

 < 



m 



z 

 m 



2 



I 



o 



CO 



H 

 > 



O 



H 

 I 

 m 



z 



CO 



> 



z 

 m 



