188 



The Potato 



do not produce fruiting bodies on the exterior, though 

 the Hving bacteria may ooze out with the sap through 

 wounds or breathing pores. 



Most shme-molds are entirely saprophytic, though a 

 few attack hving pLants. The one pro(hicing powdery 

 scab is the only example of a slime-mold disease of the 

 potato. The slime-mold differs from a fungus or a bac- 

 terium in that it consists of a naked mass of protoplasm, 

 often of many cells, in its vegetative stage. The spores 

 of the one producing powdery scab germinate as a tiny 

 mass of naked protoplasm which gains entrance to its 

 host through the lenticles or breathing pores on the tuber. 

 It passes from cell to cell within its host, infesting the 

 contents and itself greatly increasing in mass. Finally, 

 its body is transformed into spores which become exposed 

 with the rupture of the skin above them. 



CLASSIFICATION OF CAUSES OF DISEASE 



According to their causes, we may classify the diseases 

 of potatoes as follows : 



Fungous — Early blight, late blight, and rot, 

 Fusarium dry rot, Fusarium 

 wilt, Verticillium wilt, rhi- 

 zoctoniose, wart, and silver 

 scurf. 



Bacterial — Common scab, black leg, soft 

 rots, bacterial wilt, streak. 



Slime-mold — Powdery scab. 

 Non- J Curly dwarf, leaf-roll, mosaic, spindling sprout, 

 parasitic | net necrosis, tip-burn, arsenical injury. 



Parasitic • 



