[Vor. 8 
250 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
from the tests with litmus paper and the determinations of titrat- 
able acidity that the reaction of the medium might be a factor of 
considerable importance. In the experiments with some of the 
salts other than the thiosulphate, it was also realized that rather 
Dry wt. C c. 
c g ms. F lod ine 
8 4 
60 o 8 
M 
P d 
^ 
Pd 
TAS. r 
r N 
16 
a ee 
20 
y 12 16 
Days 
Fig. 1. Aspergillus niger on solution of initial Pg 4. 2 containing thiosul- 
phate. 
dry weight. 
------~---- thiosulphate decomposed expressed as cc. 
N/100 iodine. 
— - —— - —— hydrogen ion concentration. 
thiosulphate decomposed , 
+—+—+— ratio 
grow 
(The legend above holds for figures 1-3 and 7-15.) 
acid solutions were produced in some cases, and the effect of this 
factor on the ''toxie concentration" of the salt employed was 
entirely problematical. In this series of experiments the thio- 
