SOME DISEASES OF THE POTATO. 



143 



spores, but also checks the development of mites and other minute animals 

 which convey the spores from one Potato to another. 



The spawn or mycelium of the fungus extends much beyond the 

 region actually decayed, consequently it is not safe to use even slightly 

 damaged Potatos for sets, even when the decayed portion is cut off. 



Black. Scab {CEdomyces leproides, Trabut). 



This serious pest, although only quite recently imported from the 

 Continent, threatens to be quite as destructive to Potatos as the old- 

 established disease. It has also been called Chrysophlyctis endobiotica 

 (Joukn. R.H.S. xxviii. p. clxxviii) (fig. 29). 



The young " sprouts " are first attacked, presenting a dark brown 

 colour ; as these continue to grow they become contorted and much 



Fig. 27. — Wixter-rot (Nectria solani). (Gardeners 1 Chronicle.) 

 Showing outward appearance. Natural size. 



thickened, forming thick crusts of a blackish hue with projecting points, 

 and wrinkled on the surface like a Broccoli flower. After a time the 

 fungus spreads along the surface, and, meeting other diseased sprouts, the 

 greater portion of the surface of the Potato becomes covered with an 

 irregular blackish scab. 



When diseased Potatos are allowed to decay on the ground, the 

 liberated spores live in the soil and infect Potatos the following year. 



Experiments conducted at Kew prove that, if seed Potatos are 

 thoroughly well covered ,with powdered sulphur just before planting, 

 they are not attacked when planted in soil known to be infected ; but the 

 young Potatos are attacked under such circumstances ; whereas if the 

 soil is intimately mixed with sulphur, both "set " and young Potatos are 

 protected. 



It may not be practicable to mix sulphur with the soil on a large 

 scale, nevertheless the fact is worth recording. Gas-lime also kills the 



