Jan. 17, 1916 
Plenodomus fuscomaculans 
74 i 
concentration. This was diluted as shown in Table XIX, and cultures 
were made as in the preceding experiment. 
Table XIX .—Effect of quantity of food: Test with synthetic solution 
[After i month] 
Dilution. 
Pycnidia. 
Growth. 
Remarks. 
25X . 
_ 
O 
10X . 
— 
O 
5 X . 
0 
+ + + + 
White or pinkish. 
2 X. 
0 
+ + + 
Black mat formed. 
IX . 
Many. 
+ + + 
Slightly less growth than above, black mat. 
1/2 x . 
Many immature. 
+ + 
Slightly less growth than in 2X. Abun¬ 
dant evidence of pycnidia starting. 
I/ 5 X . 
10 
+ 
Growth weak. 
1/10X .... 
5 
+ 
Pycnidia extremely minute. Mycelium 
scanty. 
The experience with this solution shows that doubling the concentra¬ 
tion of a favorable culture solution increased growth, and was sufficient 
to inhibit completely pycnidium formation. A solution diluted one- 
half gave promise of many pycnidia—more than in the 1 X concentra¬ 
tion—but the pycnidia were slow in forming. In the extremely low 
concentration growth was scant and a small amount of pycnidium pro¬ 
duction took place. The experiment leads to the same conclusions as 
the preceding experiment—i. e., that a limited food supply is essential to 
fruit-body formation, and the optimum concentration is one which gives 
a comparatively large mycelial growth before the exhaustion takes place. 
The teaching of this experiment would place the limit of concentration 
of a sugar at Mjioo . We have, however, a great body of experiments 
already outlined in which pycnidium production took place with a sugar 
concentration considerably higher. For instance, in Table X pycnidia 
are reported for Raulin’s solution (cane sugar M/7) when a calcium salt 
was added. Or, considering the experiments with com grains, these seem 
to present a contradiction when it is noted that the pycnidia were first 
formed on the corn grain with its rich food supply. Similarly, the various 
laboratory media—such as prune-juice agar, parsnips, and carrots—all 
are rich in carbohydrates; yet these are reported as allowing pycnidium 
production. 
In these rich solutions, however, an extremely abundant aerial myce¬ 
lium is produced, and as the medium begins to dry the pycnidia are pro¬ 
duced in the aerial strands, but never upon the medium itself. In a few 
cases a dense mat formed over the agar, and this effectively walled off 
the new food supply. On only one laboratory medium—corn-meal agar 
(Shear and Wood, 1913)—were the pycnidia produced directly upon the 
agar. It is noteworthy that with this medium the mycelium production 
is scant. In the case of corn grains the pycnidium production does not 
take place until the corn grain is dried somewhat, and this, coupled with 
