l66 AMERICAN JOURNAL OF BOTANY [Vol. 9, 
It will be noticed by referring to figure 5 that there is no depression in 
this curve. This is due to the fact that no acidities intermediate between 
Ph 4-5 and pn 6.9 were used. The points at which the minimum occurs were 
not present in this series, and therefore no minimum was evident. Another 
Ph Potato Agar 
Fig. 5. Hydrogen-ion concentration and growth and conidial production in G. 
Sauhinetii on potato-dextrose agar — lactic-acid series. 
series with potato agar including acidities between pn 4.5 and 7.0 demon- 
strates that a minimum also occurs on potato-dextrose agar. In order to 
obtain these intermediate values, a solution of lactic acid one eighth the 
strength of that employed in the former experiment was used. The data 
for this experiment are given in table 4 and represented graphically in 
figure 6. 
Table 4. Hydrogen-ion Concentration and Growth of Gibberella Sauhinettii on Potato-dex- 
trose Agar in which the Reaction was Adjusted by Means of Lactic Acid 
Drops of 50 Percent 
Average Diameter of 
Average Diameter of 
Average Diameter of 
Lactic Acid per 20 
Ph 
Colonies after 
Colonies after 
Colonies after 
Co. of Medium 
19 Hours (Mm.) 
24 Hours (Mm.) 
43 Hours (Mm.) 
0 
7.3 
12.42 
17.06 
34.26 
1/16 
7.0 
13.86 
18.00 
34.26 
1/8 
6.0 
14.12 
17.32 
32.60 
2/8 
5-7 
12.00 
15-94 
31-30 
3/8 
5-2 
10.50 
14.92 
30.64 
4/8 
5-0 
12.48 
16.28 
30.72 
6/8 
4.65 
11.04 
14.40 
28.48 
I 
4.4 
10.64 
13.66 
25-74 
2 
4.0 
9.38 
11.60 
21.00 
3 
3.8 
7.70 
9.64 
17.30 
4 
3.6 
5.60 
7.48 
13.78 
3-5 
370 
5-14 
10.50 
From the curve in figure 6 it can be noted that a depression in the growth- 
acidity curve similar to those on liquid media is obtained on potato-dextrose 
