FUNGOUS DISEASES. 



121 



usually at or near the margin. Careful examina- 

 tion shows that the veins in the dead areas are black- 

 ened. These spots enlarge, following down the 

 veins toward the stem. The disease upon reaching 

 the stem may pass up or down it into other leaves,, 



Fig. 25 Diseased Cabbage Stem. 



and once established there it rapidly spreads thus 

 through the entire plant. 



The germs which are the cause of the malady 

 spread exclusively through the vessels or fibrous 

 portions of the tissue. These invaded vessels turn 

 black, and this striking discoloration is a valuable 

 diagnostic feature of the disease 'which every cab- 

 bage grower should learn to recognize. Fig. 25 

 shows the black spots in the leaf scars. These spots 



