THE CULTURE OF THE POTATO. 57 



ently healthy tubers may be used immediately, and 

 all peelings burnt. On no account should any be 

 kept for seed. It must ever be kept in mind that 

 the chief means of spreading this disease and in- 

 troducing it to otherwise free soil is by planting 

 affected tubers, and this requires to be closely watched 

 when purchasing seed potatoes. No remedy has been 

 discovered for the disease, except that of starving 

 out the fungus by planting in diseased areas only 

 immune varieties. This, fortunately, it is possible 

 to do, and still obtain good crops. The following 

 varieties, amongst others, have been proved immune 

 from the disease : 



Early. Resistant Snowdrop, Crown Jewel. 



Second Early. Edzell Blue, King George, The 

 Ally, Burnhouse Beauty, Conquest, Mr. Bresse. 



Main Crop. Great Scot, The Lochar, The Provost, 

 Abundance, Majestic, Rector, Kerr's Pink, Templar, 

 Lang worthy, Golden Wonder. 



Corky Scab (Spongospora subterranea). In its 

 early stages this disease appears in the form of small 

 conical or rounded elevations on the surface of 

 young potato tubers. These warts are at first 

 covered with the skin of the tuber, but soon become 

 brown in colour and rupture the covering skin. (See 

 Fig. 9.) After this stage is reached large numbers 

 of spores are produced and set free, and in this way 

 the soil becomes contaminated. If the disease 

 remains limited to this stage, only the surface of the 

 tuber is affected, and the damage for eating purposes 

 is not serious. When, however, the disease assumes 

 its severe form actual destruction of the flesh of the 

 tuber takes place, producing a more or less cankered 



