24 
Research Bulletin No. p 
get the exceedingly frequent phenomenon of large plants, usually 
with many small tubers, wilting down suddenly after the last 
irrigation. The frequent occurrence of aerial tubers, the prevalence 
of excessive numbers of small tubers, and the occurrence of few 
abnormally large tubers on such plants is also attributable to the 
insidious manner of attack. The organisms attack the stolons and 
main stem as well as the roots. Stolons with tubers in all stages of 
maturity can be found partially or completely cut off by lesions. 
As the balance between the photosynthetic and storage centers in 
such plants is disturbed, new stolons are developed nearer and 
nearer the surface and the stolons that are not attacked develop 
abnormally large tubers. Often the plant responds to this disturb- 
ance in the assimilation-storage balance by producing swellings of 
the aerial parts of the plant, the so-called aerial tubers. Many 
large plants can be pulled up with ease, because lesions make separa- 
tion of the tops from the roots or even the basal portion of the stem 
easy. Such plants may show a comparatively sound main axis 
(hg. 10). 
Infection carried over by the mother tuber, which is frequent, 
rarely permits the growth of stems more than 20 cm. high, and 
seldom allows the development of tubers. An early attack from 
without upon the main stem leads to equally disastrous results. 
The wilts of the potato plant induced by Fiisarium spp. have 
generally been considered ^•ascular mycoses due to a clogging of the 
vascular elements. In fact, however, the symptoms are due to 
killing of the root system as much as to clogging of the vascular 
elements. It is true that members of the Elegans section, such 
as F. o.vysponim, frequent the vascular elements, spreading in these 
rather than clogging them, but it is true also that they destroy roots 
in numbers. Again, even though some have referred to this disease 
as a root disease (Smith and Swingle 35), it is stated that the 
fungus enters a root, then spreads to the stelar part, and from there 
enters other roots and stolons. Just as much damage is done by the 
persistent attack from without upon roots and stolons, as noted 
by Maxns (24). 
In the course of these experiments several questions were 
raised. The soil in these experiments surely was more severely 
