172 



BACTERIAL DISEASES OF PLANTS 



ing to this vascular invasion in the animal world? Consult Figs. 

 116 to 118. 



Variability. — How long does an attacked plant live? In 

 what varieties of field corn have you found the disease, or been 

 able to cause it by inoculations? Try many varieties, if you 



Fk;. 1 14. — .1, Afrar poured plate surface colonies of A planohadcr stewarti, B, Tj'pe 

 showing pitted centers. X 10. 



have opportunity, and make records. There is much to be 

 learned about the occurrence of this disease in field corns. 

 What occurs when, by needle-pricks, you inoculate sweet-corn 

 plants 2 or 3 feet high on the upper leaf-blades rather than on 

 the leaf -tips in the seedhng stage? What does this teach you? 

 Can you check the progress of the disease by allowing in- 



