156 



BACTERIAL DISEASES OF PLANTS 



power of sunlight (in thin-sown agar plates) ; effect of weak 

 acids and alkalis; of salted bouillons (contrast with Nos. I and 

 III). Vitality on culture-media. 



For the disease. Signs. — Determine time between inocu- 

 lation {a, by needle pricks — b, through the water-pores) and 

 first local signs of the disease. In case of plants inoculated on 

 the leaf -blade, how long before signs appear in other leaves? 



Fk;. 97. — Like Fig. 96, but shows })eginning of a cavity. X 500. 



Contrast inoculations on plants growing rapidly and slowly. 

 In case of inoculations on the petiole, how long before signs 

 appear in its blade? After the infection (blackening) of the 

 water-pore region, how long before the veins of the leaf begin 

 to show the dark stain? Describe the disease. 



Histology. — Determine by sections the occupation of the 

 substomatic region in the infected leaf-teeth. Can you trace 



