336 



DISEASES OF ECONOMIC PLANTS 



¥ 



Fig. 142. — Young ear of 

 com inoculated in tho 

 silk with diplodia. 

 After Burrill & Barrett. 



affected ear are shrunken, loosely at- 

 tached, light in weight, and darker in 

 color and more brittle than those of a 

 healthy ear. Upon breaking open an 

 ear, very small black pycnidia may be 

 seen embedded in the white masses of 

 mycelium, especially at the bases of 

 the kernels. Diseased ears left in the 

 field may develop these pycnidia in 

 such abundance as to make the grains 

 black. 



Much of the food value of the corn 

 is lost, owing to the consumption of 

 starch within the grain, as well as to 

 the prevention of starch storage. The 

 germinating power of the grain is also 

 lost. 



Upon the stalks the fungus first 

 appears as very small dark specks 

 under the rind, near the nodes, and 

 at broken places, usually in over- 

 wintered stalks. Stalks nearly three 

 years old have been found bearing 

 pycnidia. Although the green stalks 

 are not naturally susceptible, the shanks 

 are particularly so. 



The causal fungus gains entrance 

 to the ears from infected stalks which 

 bear them, and these are infected from 

 the soil through the roots. Ears are 

 also infected through the silks by wind- 



