Pig. 59. Diseases of the Potato. 



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

 powdery scab, gaIl*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 t. drawings of the organism of common 

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

 and Cunningham). 



