Jan. 17, 1916 
Plenodomus fuscomaculans 
723 
At the time of making the first reading, the cultures were exposed to the 
light for about an hour, and at the second reading they were exposed to 
strong diffused daylight for two hours. 
From a consideration of the experiments reported in these tables, it is 
evident that light is a factor directly concerned with pycnidium produc¬ 
tion. There is also a strong tendency toward increased growth in the 
dark. 
The experiment has been repeated many times, with a great number of 
duplicate cultures (60 in one instance), and always with similar results. 
The following is a typical experiment. Preparation dishes with water dis¬ 
tilled out of sulphuric acid and filter paper and with water alone were 
inoculated with spores of each of the two strains of the organism. One set 
was wrapped in a double thickness of paper such as is used in photographic 
film rolls. The dishes exposed to light were set in glass battery jars on 
the window sill. The light was made diffuse by a sheet of yellow manila 
paper tacked on the window. The dark cultures were set away from the 
window in the interior of the room. The difference in temperature was 
the reverse of the conditions in the preceding experiments, since closeness 
to the cold window more than compensated for the effect of the light. In 
this experiment after a month no pycnidia formed in the dark, while in 
every culture in the light numerous pycnidia were found. 
Table; IV .—Effect of light: Test with two strains of the organism 
Strain and conditions. 
Pycnidia. 
Growth. 
Light. 
Dark. 
Light. 
Dark. 
Strain I: 
Filter paper + water. 
25 
0 
++ 
+ + + + 
Double-distilled water. 
2 
0 
+ 
+ 
Strain II: 
Filter paper + water. 
II 
O . 
+ 
+ 
Double-distilled water. 
O 
0 
+ 
+ 
To avoid the criticism that the results observed were due to differences 
in aeration brought about by wrapping the capsules, or by the use of the 
dark closet, and to test other conditions of food supply, cultures were 
made with corn broth, and these were placed in a specially constructed 
light-tight box, which, however, allowed aeration. The box was made 
of two tubes of different diameters (7 and 9 inches), one inside the other. 
These cylinders were each 12 inches tall and toothed at the ends. A 
pair of caps were made for these cylinders. The caps consisted of a 
disk of paper about 10 inches in diameter, and a short cylinder 8 inches 
in diameter was glued to it. The joint was made light-tight with black 
paraffin. When these tall cylinders were set up with the cylinders of the 
caps fitting between them, light was excluded. The cultures were 
