Minnesota Plant Diseases. 353 



leaves, where the disease has been prevalent, should be collected 

 and burned, or plowed under, to prevent the formation of spores 

 in the following season. Certain varieties of apples are also 

 known to be more resistant than others toward this disease and 

 a proper selection may aid in combating the fungus. 



Soft rots of fruits (Penecillium, Mucor, etc.). These rots 

 include some so-called ripe rots and storage rots. The soft rots 

 are due to various fungus growths. They are, in general, molds 

 either of the black or blue mold groups. The habits of these 



Fig. 186. — Apple scab on the leaf. After Longyear. 



fungi have already been pointed out in previous chapters. They 

 are amateurs in the ways of parasitism, for they need not only 

 assistance in gaining entrance to the host, but they are capable 

 also of successfully attacking only those parts which are in a 

 resting or dormant condition. The protoplasm of such plant 

 parts, as has already been pointed out, approaches the proteid 

 condition of dead plant debris. Ripe fruits of almost all kinds 

 suffer from these rots. The rots are most destructive in moist 



warm conditions. 



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