A Dry Rot of the Irish Potato Txiber 
81 
house was kept as high as possible during the inoculation and 
immediately following it so that conditions for germination of 
spores and hyphal development might be as favorable as possible. 
No infections resulted from the 61 inoculations. In many 
cases the fungus flourished on the stems and in the wounds for a 
considerable period. On one stem a slight browning developed 
but no fungus developed in the stem. The wounded stems 
promptly developed wound cork which very often sloughed off 
with the inoculum tho in many the inoculum persisted until the 
death of the stems. In several cases the fungus renewed its 
growth as soon as the stems died, but in not one did the fungus 
enter the stem and cause a wilt. Several stems were bruised so 
severely at the time of inoculation that they soon toppled over 
and either lived on in this prostrate position or died by strangu- 
lation. Such dead stems were promptly overrun by the fungus. 
Following these failures in producing the wilt of the stems, 
the experiments were repeated on younger stems of the same 
plants. No infections could be obtained. 
Some vines of the Pearl variety were bruised with a sterile 
scalpel by cutting out a piece of the bark deep enough to expose 
the wood. Inoculum was smeared into these wounds, which 
were then covered with moistened sterile cotton which was kept 
moist for a week with sterile water. Wound cork was formed 
both in the inoculated and control stems but no infection set in. 
Twelve inoculations were made and all were unsuccessful in 
producing any wilt. Upon death of the stems the fungus lived 
upon them saprophytically. 
These experiments show quite conclusively that the fungus 
cannot infect aerial, living stems of the potato, either thru 
wounds or thru the epidermis. The experiments also show that 
the fungus does attack stems as soon as thev are dying or dead. 
(See Pis. XII to XXI.) 
Appel and Schlumberger 1911 refer to certain infection experi- 
ments with the Fusarium oxysporum of Smith and Swingle 
conducted by Kock 1909.* 
We have previously discussed certain results which show 
clearly considerable variation in the susceptibility of the tubers 
of different varieties to the dry rot. The explanation for this 
may be found in one of several factors which may here be 
mentioned. The short growing season for potatoes in western 
Nebraska and particularly the frequent occurrence of killing 
♦They say (p. 24) : "Auffallend ist bei seinen Versuchen, dass auch die 
Infectionen mit Originalkulturen des Erregers des dry rot, Fusarium 
oxysporum, nicht gelangen. Diese Impversuche fussen im wesentlichen 
auf der ursprunglichen Annahme Appels v dass die Eingangspforte fur die 
erste Infektion der unterirdiscbo Teil des Stengels sei." 
