THE CULTURE OF THE POTATO. 53 



and the immense numbers of very minute spores, 

 thus produced, are distributed from plant to plant 

 and carried over a wide area by wind and other 

 agents. In wet, dull weather the disease spreads 

 rapidly ; the spores also fall to the ground and are 

 washed into the soil, where they reach, and subse- 

 quently infect, the tubers, causing them sooner or 

 later to decay and become useless. Blighted tubers 

 at first show discoloured rusty patches just visible 

 through the skin, but more evident when the skin 

 is scraped away. At first only a small part of the 

 tuber may be attacked ; but, later, the greater por- 

 tion of it is affected, and, with the entrance of other 

 destructive organisms to the diseased parts, a soft 

 rot sets in which reduces the tubers to a pulp. 



The disease is liable to be carried over from one 

 year to another in the seed potatoes ; and as those 

 that are only slightly affected are easily overlooked, 

 the greatest care should be exercised to select sound 

 tubers from healthy plants in the first instance, and 

 seed tubers should be carefully picked over later 

 and at the time of planting. 



Spraying Potatoes. It is for the purpose of destroy- 

 ing the germinating capacity of the spores and pre- 

 venting the disease from spreading or entering the 

 tissues of the plants that spraying is resorted to. 

 Potato spraying is more important in the south 

 and Midlands of England, where the disease is more 

 prevalent and liable to commence comparatively 

 early in the season. In certain of those districts 

 also, where disease appears early, it is advisable to 

 spray second early as well as main-crop varieties. 

 In the north of England and in Scotland spraying 



