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affected, and one form of scab is produced. There is 

 no known remedy for this disease. This attack is 

 distinct from ordinary scab. The common form of 

 scab brown, somewhat cork-like blotches on the sur- 

 face of the tubers is usually ascribed to bruising in 

 one way or another. The skin of the tuber is slightly 

 abrased by the friction of the soil on it, which sets up 

 irritation or excitement, causing a special rush of 

 matter to the spot, which develops into skin. The 

 stirring of the soil rubs it against the tuber, when 

 the skin is tender and easily affected. When potatoes 

 receive a check owing to drought, when the soil 

 sometimes sets hard, the first rain is apt to cause the 

 tubers to grow, although there may not be sufficient 

 moisture to soften the ground. This causes special 

 pressure on parts, which become abrased. The split- 

 ting of the stems is also attributed to mechanical 

 causes. 



Among other minor diseases may be mentioned 

 the Peziza postuma, a fungus which pervades the 

 plant, and shortly destroys it by exhausting the 

 moisture from the leaves and stems, reducing them 

 to tinder, to prevent which no means have yet been 

 discovered. 



The ordinary dry rot is produced by a fungus, as is 

 also a more recently noticed form, called black dry rot. 

 A peculiarity of the latter is that, when the appa- 

 rently healthy portion of the tuber is cut, it assumes 

 first a rust-red colour, which subsequently turns black. 

 In some seasons a large quantity of potatoes suffer 



