592 BULLETIN 347 
these investigators call the color of the mycelium on the cut surface 
“cadmium yellow.” 
Potato agar slants 
When streak cultures are made on potato agar slants with spore horns, 
the mycelium begins along the streak as a white weft and spreads rapidly 
toward the edge. In four days, at ordinary room temperature, the orange 
color begins to appear along the streak, and it broadens as the mycelium 
grows out until the whole surface of the slant is covered with a deep 
orange growth. This test was used most extensively by the Andersons 
in distinguishing this species from the other Endothia. Shear and 
Stevens (1913 a:12) record the same phenomenon on this agar, and add: 
“ Within six days, the mycelium, especially at the base of the agar slant 
took on a peculiar granular metallic appearance. . . . This portion 
of the culture was light orange yellow by reflected light and orange by 
transmitted light. The peculiar surface appearance might perhaps be 
called ‘ brassy.’ This metallic appearance has been found to be the most 
constant and reliable distinguishing character of E. parasitica on potato 
agar. In twelve to fourteen days small pycnidial pustules appeared 
in the upper portion of the tubes, and the agar just below the mycelium 
became warbler green, changing later to olive green.” 
Often potato agar cultures after three or four months turn to a deep 
purple or wine-color. H. W. Anderson (Anderson, P. J., 1914) found 
that this purple color is due to the fact that the long growth of the organism 
on the agar causes the latter to lose its acid character and become alkalin. 
The yellow pigment (aurine) in the mycelium goes into solution in an 
alkalin medium and turns purple. The pigment then escapes from the 
cells and is suffused throughout the agar. 
Relation of light 
The fungus grows just as rapidly in darkness as in light, and also pro- 
duces the yellow pigment but not so abundantly. D.C. Babcock, work- 
ing with one of the writers of this bulletin, found, however, that in total 
darkness no pycnidia are produced, but just as soon as the culture is 
brought into light the pycnidia begin to form. This fact accounts for 
the concentric rings of pycnidia so noticeable on plate cultures. One 
circle is produced each day. Doctor Shear, in a letter to the writers, 
states that pycnidia are produced in darkness. 
Relation of temperature 
Shear and Stevens (1913 a:9) studied the relation of temperature to 
the growth of the mycelium in pure cultures. Their results are thus 
