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SOME POTATO DISEASES. 

 I. — Black Scab. 



Oedomyces leproides (Trabut). 



This parasitic fungus was first observed attacking beetroot 

 growing in the grounds of the School of Agriculture at Rouiba, 

 near Algiers. Irregularly wrinkled outgrowths, varying in size 

 from that of a pea to a walnut, originate near the top of the 

 root. These tumours or outgrowths, when mature, contain 

 numerous irregularly-shaped cavities filled with the dark coloured 

 resting-spores of the fungus. 



During the autumn of 1901 a diseased potato was received at 

 the Board of Agriculture for investigation and report from the 

 neighbourhood of Liverpool. A note accompanying the speci- 

 men stated that nearly all the potatoes were attacked by a 

 similar disease. Microscopic examination showed that the 

 disease was identical with the one attacking beetroot as described 

 above. During the present season potatoes attacked by this 

 disease have been received from widely separated localities in 

 England. An English-grown beetroot attacked by the same 

 disease has also been examined. 



On the potato the fungus does not cause tumour-like out- 

 growths, but a continuous rough or nodulose, black, scab-like, 

 thick crust, which commences at one or several distinct points, 

 and finally covers the entire surface of the potato. 



The central portion of diseased tubers remains sound for 

 a considerable period ; in fact, the fungus never spreads beyond 

 the surface layer, and if left lying on the ground the entire 

 tuber becomes dry and eventually crumbles to pieces, thus 

 liberating the resting-spores into the soil, where they remain in 

 an unchanged condition until the following year. 



The disease is most prevalent on dry sandy ground. 



Preventive Measures. 



Diseased roots and tubers should be very carefully collected 

 and burned or deeply buried, because if allowed to rot on the 



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