Bull. 20, Div. Veg. Phys. & Path., U S. Dept. of Agriculture. 



Plate XXIX. 



o 

 $ 



m 



3) 



O) 



-D 



> 



-< 



tn 



33 



C 

 m 

 > 



CO 

 > 



z 



00 



> 



33 

 DtJ 

 > 

 33 

 > 



o 



> 



