x 
500 
high hydrogen ion concentration is reached, 
and furthermore, that these four organisms 
respond in about the same way, though there 
are distinct variations among them. Further- 
more, as might be expected, the curves ob- 
tained are similar to those showing the rela- 
tion between enzyme activity and hydrogen 
ion concentration. 
The most important facts to be presented 
here can be shown by means of a general curve 
setting forth the general behavior of the four 
fungi studied. The curve shown in the ac- 
companying figure is constructed by plotting 
as ordinates the weights in grams of mycelium, 
produced in about five weeks’ time upon media 
of varying P,, values as represented by the 
abscissae. This curve shows in a very general 
way the mean of the individual curves for the 
different fungi when grown upon the two 
media. The weight of mycelium produced 
shows large variation among the individual 
curves while there is rather close agreement 
in the P,, values which are physiologically im- 
portant to the various fungi. 
In the fcilowing discussion we shall speak 
of the “ first critical point,” meaning the P,, at 
B (figure), the point where the first marked 
deflection in the growth curve appears; the 
“ second critical point,” meaning the Px at C, 
where the second marked deflection in the 
opposite sense occurs in the growth curve; and 
the limiting acidity,” meaning the Pu at D, 
where practically no growth occurs. By 
“critical range” we shall mean the range of 
the P,, values included between the first and 
the second critical points. 
The curye in the accompanying figure is 
drawn with the portion AB horizontal. In 
the individual curves—that is for a single 
fungus on a single medium—this part may be 
horizontal or may slope either up or down in 
passing toward B. Or again, in passing from 
A toward B the curve may rise to a maximum 
and then fall toward the critical point B where 
a sharp inflection downward occurs. Such a 
maximum, when present, usually occurs nearer 
B than A—that is, at a Pu of about 3.0. The 
critical points stand out more sharply in some 
than in other curves and the first critical 
SCIENCE 
[N. S. Von. XLVIII. No, 1246 
point is usually more pronounced than the 
second critical point. The slope between B 
and C shows a rather large variation in the 
A 
= 
La fleence of 
Ag deegen Lon, Concentrefion 
i “upen 
the Growth of 
Four WeadDeslreying Fung? 
a arl fice! aedta. 
Weight of —ycelium in groms 
8 
Fie. 1. 
individual curves. In some cases the line be- 
tween these two points is nearly vertical. In 
this curve the point D appears as a rather 
abrupt point. Point C often occurs nearer 
the lower axis and the portion of the curve CD 
occurs more nearly horizontal with a more 
or less uncertain termination. However, the 
limiting Pg value appears to be in the region 
of 1.7. 
Translating these data into terms of nor- 
mality, the first critical point occurs at about 
1/350 normal, and the limiting acidity at 
about 1/50 normal, hydrogen ion concentra- 
tion. 
Merte R. Mracnam 
Tur NEw YorK STATE COLLEGE OF FORESTRY, 
SyRACUSE UNIVERSITY 
SCIENCE 
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