20 Research Bulletin No. g 



F. oxysporum makes greater headway than the other and there 

 causes a vascular mycosis more frequently, which accounts for its 

 designation as a vascular parasite (rigs. 7 and 8). 



Discussion. — If plants, experimentally inoculated, showed 

 only light symptoms to begin with, most of them continued their 

 growth with symptoms less severe than those shown in the held. 

 If they showed severe symptoms early, these proved more severe and 



A B 



Fig. 6. — Wilt and death of potato plants produced in laboratory with Fusarinm 

 trichothccioides, 12 days after inoculation; Early Ohio variety; wilting is restricted 

 to the side to which inoculum was applied. 



more rapidly fatal than those in the field. The organisms in the 

 field work much more insidiously, attacking the roots of the plant 

 slowly but progressively, and permitting the plant, except in extreme 

 cases, to readjust for its water requirements. These readjustments 

 manifest themselves in the curling and rolling phenomena 

 (figs. 4 and 9). 



Potato plants in the irrigated sections show this phenomenon 

 nicely. As long as cultivation and irrigation are maintained, the 

 plant develops new roots progressively higher up, and the infected 



