Family Convolvulaceae 175 



ing the effect of damping off. In examining an 

 infected sprout it will be found that in the earlier 

 stages of attack the foot of the plant is soft, water- 

 soaked, and covered at the exterior by fungus 

 threads. Later this growth becomes thick, giving 

 the appearance of fluffy cotton placed at the foot of 

 the sprout. Soon after, the cottony mycelial growth 

 anastomoses, then disappears, giving birth to small 

 roundish brown bodies like mustard seed known as 

 sclerotia. 



Sclerotium Rolfsii seldom attacks mature sweet 

 potato roots. However, when the fungus is arti- 

 ficially inoculated in sound roots, a punky dry but 

 slow rot is the result (fig. 27 f). For further dis- 

 cussion of this fungus as it attacks other hosts see 

 P- 305. 



TEXAS ROOT ROT 

 Caused by Ozonium omnivorum Shear. 



So far as is known, this disease occurs only in Texas, 

 New Mexico, Oklahoma, and Arizona. The disease 

 is of great economic importance in these States, since 

 numerous other crops are subject to its attacks. 

 The symptoms of Texas root rot are a girdling of the 

 vines at the stem end, and a similar effect on the roots 

 (fig. 27 e and fig. 28 g and r). In these cases, the 

 epidermis and cambium may be readily slipped off 

 from the main body of the infected stem and root. 

 For a more detailed account of the Texas root rot, 

 see okra, p. 297. 



