254 



DISEASES OF ECONOMIC PLANTS 



wise sound : or again several scales may be rotted. If the 

 outer scale is rotted, the bulbs are designated as " slippery 

 onions " by the growers. The rot does not spread from 

 scale to scale within the bulb. In storage it does not 

 progress rapidly in dry onions, but wet onions do rot 



Fig. 113. 



-Onion affected with soft rot; longitudinal and cross section. 

 Stewart. 



After 



rapidly. The only suggestion toward control is to keep 

 the onions dry in storage. 



Black mold (Macrosporium ■parasiticum Thuem.). — Fre- 

 quently onion leaves which have been injured by some 

 cause, also old stems or seed stalks, assume a velvety, black 

 coating which often covers them entirely. This condition 

 follows only upon previous injury, weakening, or death, 

 from some other primary cause, chiefly as a sequel of the 

 downy mildew. Though not a primary disease its pres- 

 ence extends the injury started by other causes, breaks 



