Fusarium of Tuber Rot and Wilt of Potato 



19 



the whole plant took place, the fungus girdled the whole stem, 

 while plants that were not girdled lived on, even though one side 

 was entirely destroyed. There was little lateral and subsequent 

 vertical spreading of the fungus from one vascular strand to the 

 other. These experiments were repeated with 25 other plants and 

 in most cases the same symptoms were observed. These symptoms 

 have been repeatedly observed in the dry land areas of Nebraska, 



J 



B 



Fig. S- — Rosette produced in laboratory with Fusarium oxysporum, and control 

 plant; A, control, Early Ohio variety; B, resetted plant, 10 days after inoculation, 

 Early Ohio variety. 



but have always been looked upon as cases of "sun scald," and 

 and in previous experiments with wilting due to F. Irichothecioides 

 such cases were ignored. 



Plants grown in soil infected with F. oxysporum and F. tricho- 

 thecioides showed severe lesions of root and stolons. Examination 

 of roots affected with either organism showed that the cortical 

 regions are first and most severely attacked, not only intercellularly, 

 but also intracellularly, the cells being packed full with hyphae. 

 In most cases the cortex could be sloughed off with exceeding ease. 

 From the cortex the organisms invaded the stelar regions, where 



