a 



g 



FIG. 59. DISEASES OF THE POTATO. 



a. Powdery scab, early stage, b. powdery scab, advanced stage of rotting, c. and d. 

 powdery scab, gall-forming stage on potato roots (c. and d. after Melhus and Rosen- 

 baum), e. single potato cell showing spore balls of the powdery scab fungus (after 

 Melhus), /._ black leg, _g. common scab, h. to i. drawings of the organism of common 

 scab, showing branching of threads and groups of spores or conidia (after Lutman 

 and Cunningham). 



