750 



Varieties of Scab in Potatoes. 



[Jan., 



gradually assume a blackish colour with age, due to the 

 presence of myriads of dark-coloured spores belonging to the 

 fungus causing the disease. 



The young "sprouts " only are attacked by the fungus, the 

 substance of the tuber at first remaining free from injury. 

 When a sprout is attacked, the irritation set up by the fungus 

 causes an excess of food material to enter the infected area, 

 which rapidly increases in size and spreads over the surface 

 of the tuber. In cases where several sprouts are attacked, 

 the entire surface of the tuber often becomes covered with 

 an irregular, cauliflower-like mass. 



In some instances, when the haulm is lying on the ground, 

 the young leaves are attacked and distorted by the fungus; 

 very young tissue, in fact, of any portion of a potato plant 

 appears to be liable to infection. 



When the fungus spores are mature the warts commence 

 to break up and decompose, thus liberating the spores, which 

 pass into the soil. At this stage various kinds of fungi and 

 bacteria gain an entrance into the tuber and complete its 

 destruction. 



After years of failure, the spores of the fungus causing 

 black scab have at last been induced to germinate. This 

 advance enables the systematic position of the fungus to be 

 determined with certainty, and will also aid in formulating 

 preventive measures, now that its life-history is known. 



Scab caused by Millipedes. — Among the various kinds of 

 millipedes, popularly known as " false wire-worms," Julus 

 pulchellus, L., is the greatest enemy to growing potatoes. 

 It varies from half to three-quarters of an inch in length, and 

 is not much thicker than an ordinary pin, pinkish-white in 

 colour, with two rows of small purple spots running its entire 

 length. Although not generally a primary cause of injury, 

 Julus reaBily takes advantage of any minute wound, which 

 it quickly enlarges by feeding on the sound portion of the 

 tuber. In some instances numerous shallow cavities are 

 formed in the flesh of the potato, and as each wound becomes 

 surrounded by a raised border of wound-cork, a scabbed 

 appearance results. In other instances small holes roughly 

 circular and of varying depth are produced, whereas in some 

 cases, as when following on an attack of Spongospora scabies y 



