Diseases op the Potato. 



301 



present ; the contrary is also true. The decay does not take place 

 in a uniform manner, 

 but its progress varies 

 in different tubers. In . 

 some it is mostly the 

 parts near the surface 

 that are affected, while 

 in others the disease 

 may advance rapidly 

 towards the center 

 of the tnber, causing 

 the exterior to show a 

 much smaller amount 

 of disease than is ac- 

 tually present. The 

 discoloration, however, 

 generally presents a 

 uniform appearance. 

 Although it is by no 

 means impossible for 

 the mycelium to reach 

 the tubers from the 

 leaves by means of the 

 stems, still it is the gen- 

 erally accepted opinion 

 that infection does not 

 take place in this man- 

 ner. This belief was 

 was held many years 

 ago, for in some of the 

 earlier writings recom- 

 mendations may be 



found in which very high hilling is advocated so that the spores 

 may be w^ashed past the tubers and away from them, and not 

 through the soil directly to them. 



There is still another feature of the late blight which it is well 

 to bear in mind. The disease generally appears during August 

 and September, although earlier and later attacks are not very 

 rare. Coming so late in the season, all the earlier varieties are 

 comparatively free from attack, but the later ones are especially 



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