Family Convolvulaceae 157 



bruised. Where this is the case, a black mass of 

 short-stemmed sporangia or fruiting bodies of the 

 fungus are formed at the crack (fig. 25 g), through 

 which opening the liquid from the root drips. When 

 no such cracks are formed, the fungus fails to fruit 

 and the roots dry by gradual evaporation through 

 the epidermis. 



Resistance to Soft Rot. While soft rot causes the 

 greatest damage to sweet potatoes in storage, not all 

 the roots alike are susceptible to its attack. There 

 is a certain per cent, of the crop which when housed 

 poorly will soft rot shortly after the potatoes are 

 taken into storage, while another per cent, seems to 

 possess a degree of resistance. These latter will 

 usually keep for a month or two and then rot, par- 

 ticularly if the winter is mild and the roots undergo 

 what is known as the second sweat. There is a 

 third class of root which seems to be resistant for a 

 long time. 



Odor of Soft Rot. Often storage men claim that 

 soft rot emits strong, disagreeable odors. Observa- 

 tions show that soft rot in bins is odorless for a week 

 or ten days, after which time fermentation sets in, 

 and an odor is quite noticeable. After a short time, 

 the affected potatoes will become fairly dried out 

 and other fungi such as Diaporthe batatis, Ftisarium 

 batatoMs, Sclerotium bataticola, and a number of sap- 

 rophytic fungi gain entrance. Sometimes putrefac- 

 tion follows the acetic fermentation. 



Soft rot is not carried from year to year in the 

 dried-out roots which were previously destroyed by 



