1907.] Winter-Rot of Potatoes. 



739 



This fungus is one of the commonest diseases of the potato. 

 It attacks stored potatoes, and is always present to some 



extent, but as a rule only reaches the 

 '^•■'^mato^^^^ proportions of an epidemic during hot, 

 {Nectria solani, Pers.) seasons, which favour the rapid 



development and spread of the fungus. 

 The tubers only are attacked, and inoculation, through spores 

 present in the soil, takes place when the tubers are young ; 

 but, as a rule, there is no obvious disease present when the tubers 

 are lifted, although the mycelium of the fungus is present in the 

 tissues. The further extension of the disease depends en'.irely 

 on circumstances. If the potatoes are kept dry and exposed to 



Winter Rot {Meclria solani). 



the air no further development takes place. On the other hand, 

 if they be stored or placed in heaps so that air is practically 

 excluded, and more especially if stored before being perfectly dry, 

 sweating takes place, the temperature is raised, and within a 

 few weeks the mycelium present in the tubers commences growth. 

 The first external indication of disease is the gradual depression 

 and shrivelling of a portion of the surface of the tuber ; these 

 sunken portions are soon more or less covered with white 

 patches of the fungus, bearing myriads of spores, which are 

 quickly distributed by mites and other minute creatures. 

 At a later stage the white tufts change to a pale pink colour, 

 and produce a second crop of spores, which in like manner are 

 distributed through the heap of potatoes by mites. &c. By 



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