422 
AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
done in figure 2, we secure a curve having a double maximum with a 
minimum between at a pH of 5.75-5.8. The curves given in figure 2 are 
those for 12 and 48 hours. 
Fig. 3. The gain in weight of 10 g. of potato-tuber tissue in 150-cc. quantities of 
0.01 M phosphoric acid and 0.01 M sodium hydroxide in 12 hours. 
In the third experiment the dilute buffer mixtures were again used, but 
what appeared to be the critical region of hydrogen-ion concentration was 
covered with a greater number of solutions. In this case the reaction at the 
alkaline end of the series changed toward greater acidity. This change was 
evident in solutions of pH greater than 5.75. An examination of the in- 
Table 3. Gain or loss in weight of 10 g. of potato-tuber tissue in 6; 12, and 24 hours in ijo-cc. 
quantities of buffer mixtures of 0.01 M Na citrate and 0.01 M NaOH, the buffer 
mixtures being replaced with fresh quantities at each weighing 
Sol. No. 
Initial pH 
pH 
after 
6 Hrs. 
pH 
after 
12 Hrs. 
pH 
after 
24 Hrs. 
Gain or 
Loss, 
6 Hrs. 
Gain or 
Loss, 
12 Hrs. 
Gain or 
Loss, 
24 Hrs. 
I 
5 -i 
54 - 
54 
5-3 
g- 
O.158 
g- 
— 1.192 
g. 
-I.925 
2 
5 - 2 - 
54 
54 
54 
O.248 
— 1.410 
— 2.068 
3 
5-5 
5-5 
5*5 
5-5 
0.066 
— I.608 
— 2.067 
4 
5-67 
5.67 
5.67 
5.67 
O.125 
-I.525 
-2.083 
5 
5-8 
5.8 
5-8 
5-8 
O.316 
-I.258 
- 1.947 
6 
6.0 
6.0 
6.0 
5-8 
0.333 
—1.242 
— 2.092 
7 
6.1 
6.2 
6.0 
5-8 
0.558 
— 1.017 
-I.767 
8 
6.2 
6-3 
6.0 
5-8 
O.566 
-O.825 
- 1.758 
9 
6.4 
6-3 
6.2 
6.0 
O.716 
- 0.750 
— I.617 
10 
6.7 
6.8 
6.6 
5-8 
1.000 
-O.125 
— I.250 
11 
6.8 
6.6 
6.7 
6.4 
1.566 
I.442 
1.583 
Redist. 
H 2 0 
