Family Convolvulaceae 167 



under the epidermis, and the latter is ruptured at an 

 early stage (fig. 26 f). They are also formed through 

 the interior tissue of the infected root, and it seems 

 that in this case the spores can escape only when the 

 roots break up and disintegrate. x 



TRICHODERMA ROT 



Caused by Trichoderma Koningi Oud., and Tricho- 

 derma lignorum (Tode.) Harz. 



The symptoms of several of the different rots on the 

 sweet potato are often so similar that it is difficult to 

 find appropriate, popular names with which to char- 

 acterize each disease. Trichoderma rot by itself 

 does not exist under the average storage conditions. 

 But it follows other rots, particularly ring rot, and 

 soft rot, causing further destruction of the partially 

 affected roots. Trichoderma rot is a storage trouble 

 only, and the causative organism is no doubt brought 

 in from the field adhering to particles of soil. 



Symptom. In the earliest stages, the spots are 

 circular, and of a light brown color, with a tendency 

 to wrinkle. The flesh is hard and watersoaked, 

 brown in color with a black zone in the region be- 

 tween the healthy and diseased tissue (fig. 27 a). 

 The spot enlarges in all directions and eventually 

 destroys the entire root. When the decay is well 

 advanced, a very luxuriant, white, mycelial growth 

 is formed on the surface. Spores are produced very 



1 For further details of this fungus see Taubenhaus, J. J., Ameri- 

 can Jour, of Bot., 2 : 324-3-31, 1915. 



