68 
Research Bulletin No, 1 
Delacroix* 1906 in a discussion of the black-leg of potatoes 
due to Bacillus phytophthorus expressed doubt as to the causal 
relation of Fusarium oxysporum to the wilt and dry rot described 
by Smith and Swingle. 
COMPARATIVE STUDIES OF FUSARIUM OXYSPORUM AND FUSARIUM 
TUBERIVORUM. 
In order to compare the behavior of the organism isolated from 
Nebraska tubers showing dry rot with the Fusarium oxysporum 
assigned by Smith and Swingle as the cause of a wilt and dry rot 
of the potato, we requested Dr. Smith to send us a culture 
of the organism with which he worked. Unfortunately these 
original cultures had died but Dr. Smith requested Mr. W. A 
Orton, also of the Bureau of Flant Industry, to send cultures of 
an organism considered by him to be the same as the one with 
which Smith and Swingle had previously worked. This organism 
had been isolated by Orton from tubers, showing dry rot, secured 
from the Pacific Coast. 
A close study of this Fusarium oxysporum and of the Nebraska 
Fusarium was undertaken in 1000 with special reference to the 
points which Smith and Swingle had emphasized. The relation 
of color formation to various kinds of light, to darkness, and to 
the kind of medium used was studied carefully. The influence of 
these factors upon the habit of the fungus was observed as well. 
The work soon showed that the two organisms were not 
identical and the Nebraska fungus was set aside as a new species. 
The results of these studies are found in Tables 24 and 25. 
MORPHOGENIC AND CHROMOOENIC INFLUENCE OF ACIDITY OF THE 
MEDIUM UPON FUSARIUM OXYSPORUM AND 
FUSARIUM TUBERIVORUM. 
The solutions of the acids were made by dissolving the gram 
molecular weight of the acid in grams in water to make a 
liter of solution. These solutions are here referred to as N|l 
solutions. Different amounts of these solutions were then added 
to the rice. For example, -j-100 acetic acid, as employed in the 
table, means that 5 c.c. of the N|l solution were added to 50 c.c. 
of water and that 2 c.c. of this solution were added to 2 £rams 
of nVe kernels. The tubes were then autoclaved in a slanting 
position for 15 minutes at 110° C. 
* He says (p. 1353): "De plus, j'ai pu constater que le bacterie, qu'il 
6'agisse du Bacillus solanicola, aussi bien que du Bacillus phytophthorus, 
est presque toujours accompagnee d'un mycelium de Fusarium; ce myce^ 
ilum, qui, d'apres nos recherches, n'est pas parasite, n'apparait, dans un 
cas comme dans l'autre, que secondairement. On ne le rencontre pas sur 
la plante quand la maladie est a son debut et j'incline k penser que lea 
cas do parasitisme du Fusarium oxysporum r£cemment decrits en Amer- 
ique par E. F. Smith et D. B. Swingle sur la pomme de terre ne sont 
peut-etre que des faits analogues a ceux que je dScris." 
