Family Convolvulaceae 171 



they are more appropriate than the name "stem 

 rot." 



Symptoms. There is no doubt that "stem wilt" 

 has its origin in the seed bed. In badly infected 

 soils, it is often difficult for the plants to get a stand, 

 as they die a week or two after being put out. They 

 first lose their green color, and turn pale, and' when 

 they are pulled out, they will be found to be cracked 

 lengthwise because of the swelling. The presence of 

 stem wilt may easily be determined by inserting the 

 nail into the stem and peeling off a piece of epidermis 

 and cambium ; the vessels will be found to be a brown 

 color. Frequently the stem is covered with a pink- 

 ish layer of sickle-shaped spores of the Fusarium 

 parasite. Often, and particularly in moist seasons, 

 infected sprouts continue to grow, sometimes until 

 digging time, and even produce fair sized roots, pro- 

 vided no secondary invaders set in to destroy the 

 hill. Sometimes black rot, as a secondary parasite, 

 sets in at the base of the stem near the ground, kill- 

 ing the bark or covering of the stem, thus shutting 

 off all food supply, and resulting in the dying of the 

 entire hill in a short time. Frequently a wet bacte- 

 rial rot starts in the base of the plant where black rot 

 has followed stem wilt. This stage helps to convey 

 the erroneous impression that stem wilt induces an 

 actual rotting in the field. Yellowing of the affected 

 stems and vines, while a frequent symptom, is not 

 always pronounced. Often the disease in plants 

 can hardly be detected, as the fungus is hidden inter- 

 nally in the fibro-vascular bundles and the roots main- 



