A striking feature of this fungus is that it causes the complete 

 breaking down of the infested tissues of the host-plant into a slimy, 

 putrescent, ill-smelling mass. Most fungi weaken or kill by gradu- 

 ally sapping the vitality of their hosts, but here is no half-way work, 

 no uncertainty as to whether fungus or host will win in the struggle. 

 The development of the fungus and accompanying death of the 

 tissues of the host is usually quite rapid, and in very violent cases 

 most astonishingly so, forty-eight, or even possibly twenty-four, hours 

 being sufficient to convert an apparently flourishing field into a putrid 

 mass. This destruction of the " tops " is commonly known as the 

 blight. Extreme cases like this can only occur, however, when 

 atmospheric conditions are very favorable, in wet, sultry weather, 

 with a wind which serves to carry the spores freely and in the right 

 direction. At best, however, the rapidity of its development is the 

 one element which makes this fungus ver}' difficult to deal with. 



But while the killing of the potato tops while in vigorous growth, and 

 the securing of a much reduced crop would be a sufficiently serious mat- 

 ter, the trouble does not stop there. After killing the tops the fungus 

 penetrates through the stems to the tubers and causes a similar rapid 

 decay in them also. It is to this destruction of the tubers that the 

 name rot is commonl}' applied, and the belief is quite general that 

 the blight and the o'ot are due to different causes. This, however, is 

 not the ca^e, and it is as well to designate both by the name rot. 

 The only hope of saving the tubers when the tops begin to show 'the 

 disease, is to dig them at once, which can often be done before the 

 fungus reaches them, when the progress of the disease is not extremely 

 rapid. It should be said, however, that many writers believe tliat 

 the parasite can reach the tubers through the medium of the soil, 

 as well as through the stems. 



In mild forms of the disease, the tubers often become infected by 

 the threads of the fungus without suffering much decay. If such 

 tubers are stored in a comparatively warm place for the winter, the 

 fungus may continue its destructive development within them and even 

 infect neighboring tubers. Frequent picking-over and a cold place 

 for storage are the chief preventives of loss from this source. 

 Infected tubers, planted in the spring, are very likely to produce 

 diseased plants, from which a whole field may become diseased. 

 Care should, therefore, be exercised in selecting "seed" potatoes, 

 that none of them bear the brown decayed spots which indicate the 

 presence of the rot fungus, though it is irue that sound crops have 

 been raised from infected " seed". 



