188 



Tlir Potato 



do not produce fruiting bodies on tlu> exttTJor, though 

 tho Hving bacteria may ooze out with tlic sap througli 

 wounds or breathing pores. 



Most slime-molds are entirely saprophytic, thougli a 

 few attack living plants. The one iiroducing powdery 

 scab is the only example of a slime-mold <Usease of the 

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

 terium in that it consists of a naked mass of ])r()t.oi)lasm, 

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

 of the one producing powdery scab germinate as a tiuN' 

 mass of naked protoplasm which gains entrance to its 

 host through the lenticles or breathing ]K)res 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 transformetl 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- Curly dwarf, leaf-roll, mosaic. sj>indling sprout. 



parasitic 1 net necrosis, tip-burn, arsenical injury. 



Parasitic • 



