Research Bulletin No. 1 
light, the fungus is white, but as soon as exposed to light a 
distinct color develops. In the former case slight conidial forma- 
tion is the rule, while in the latter great numbers of conidia are 
formed. 
When grown on stems considerable variation in color ap- 
peared. When grown on young stems of a tuber grown under 
irrigation a rich pink color is developed but when grown on 
stems of a dry land variety the white color predominates. Thi? 
may in age turn to an ochre tint. 
Microscopically no difference can be seen. The cell sap is 
always of the lilac mauve color in all cultures, both in mycelium 
and in the spores. By putting the mycelium which has been 
grown in distilled water into strong mineral acid a red color 
often sets in. 
The cell sap is always blue. When the growth is weak and 
no color is developed in the plasma and wall the cell sap color 
is visible in the mat. If conditions are not favorable for growth, 
changes in the plasma and walls obscure the cell sap color so 
that the mycelium is white. Macroscopically the spores are al- 
ways pink. This color must be located in the plasma or wall and 
since the nature of the medium determines whether conidia will 
be formed or not it will also determine whether a pink color will 
appear or not. The light has an effect in so far as it catalyti- 
cally influences the medium or in so far as it stunts the growth 
of the mycelium, causing it to go over into conidial formation. 
It might do this either by increasing the respiratory activities in 
the fungus or by inhibiting them. 
In the 1 per cent sugar solution in light, the medium must be 
of such a nature as to produce color and not to cause conidial 
formation. On beef bouillon (+10) a slight aerial growth took 
place, few conidia were formed, and a very faint pink color 
resulted, so faint that it was scarcely visible. 
Color therefore is constant as long as the organism is grown 
under ordinary constant conditions. The substratum and other 
environmental factors, especially light, can influence it slightly 
however. The color is always in the pink category, and no com- 
plete changes from red to blue or to yellow, as we have found in 
the Fusarium from Colorado, are obtained in Fusarwm tuberi- 
vorum. It is apparent that the nature of the medium and light 
has something to do with development of color in this organ 
ism. Which of these is the determining factor we have not been 
able to ascertain. 
If a suspension of old spores is made in water, or when the 
fungus is grown on liquid media for 6 or 8 weeks, the liquids 
take on an ochre color. This probably is due to an oil which 
completely fills the conidia when they are old. 
