924] 
WOLPERT—FUNGI AND H-ION CONCENTRATION OF MEDIA 89 
Considering the 2 major solutions, the Richards' and the pep- 
tone solution with sugar, Lenzites sepiaria is the most active 
producer of acid, the final Ру in every ease being more acid than 
that produced for the corresponding solution by the other species 
(table xvi). However, in the peptone solution without sugar 
and in the Richards' solution with cellulose as the carbon source, 
this tendency toward greater final acidity is not evident. Table 
хп shows that in 4 out of 5 cases in the peptone sugar-free solu- 
tion, the active acidity is actually decreased by Lenzites sepiaria. 
TABLE XVII 
THE AVERAGES OF THE FINAL Рн PRODUCED IN THOSE 
SOLUTIONS IN WHICH THE FUNGI GREW 
Solutions 
: , Peptone Peptone 
Fungi Richards’ . with sugar without sugar 
"Ee: G. °C 
15 25 35 15 25 35 25 
РІ. ostreatus 5.1 4.5 4.6 6.7 6.9 6.9 6.6 
. adustus 5.5 5.9 5.8 4.6 5.8 6.3 5.8 
Ph. adiposa 5.1 4.8 4.6 6.0 5.5 5.9 6.1 
L. sepiaria 46 4°42 | 291 935 1 331 35 6.1 
8. commune 4.8 4.5 4.6 5.6 5.7 5.9 5.4 
P. versicolor 5-1 4.4 4.6 4.8 4.7 4.7 5.4 
D. co 43 |] БО | 49 | £9 | 05 | 653 6.1 
А, mellea 5.1 4.9 4.7 4.6 4.5 6.2 6.2 
While Polystictus versicolor does not cause such a sharp acid re- 
action in the substratum upon which it grows, and while the 
results vary with the medium, this fungus does tend to increase 
the acidity of all the solutions. The other 6 species are less 
consistent than these 2 fungi toward increasing the active 
acidity of the major solutions. Zeller, Schmitz, and 
(19), using 12 species of fungi, found in general that all except 
Merulius pinastri increased the active acidity of а potato broth- 
nutrient salt solution and that Polystictus versicolor increased the 
active acidity in 7 and slightly decreased it in 4 cases. It is 
evident that the direction of the change in the initial acidity 
- depends upon a variety of factors. 
These factors beyond a doubt are not wholly dependent upon 
the individual physiological action of the fungus. Undoubtedly 
the chemical nature and the initial acidity of the substratum 
