420 
AMERICAN JOURNAL OF BOTANY 
[Vol. io. 
0.09 g. It is noteworthy that in this solution the weight of the potato 
remained almost constant at all three weighings. In the other buffer 
mixtures the loss in weight varied from 0.29 g. to 0.66 g. with the majority 
around 0.50 g. 
If the gain or loss in weight is plotted against the average hydrogen-ion 
concentration of the solutions expressed as pH, the curves given in figure I 
are obtained. The results secured at the end of 8 and 24 hours are given 
there. The curve for the 12-hour period is very similar to that for 8 hours, 
and to avoid confusion is not included in the figure. An examination of 
figure 1 shows that a smooth curve drawn through the points forms a curve 
in each case with a double maximum, a minimum occurring between at a 
pH of 5.8 to 6. If all points were connected, a W-shaped curve would result 
around pH 6.0 with a peak at pH 6.05. This has not been done in the figure. 
A consideration of the probable error showed that the minimum at pH 
5.8-6.0 could not be accounted for by variation. 
In order to reduce the effect of the ions other than H and OH present in 
the buffer mixtures, the solutions described above were diluted 10 times for 
the second experiment. The results are given in table 2. There it can be 
noted that, with less buffer action due to the dilution, the potato produced 
a greater change in the reaction toward alkalinity at the acid end of the 
series than was noted with the more concentrated mixture. A change in 
Fig. 2. Gain or loss in weight of 10 g. of potato-tuber tissue in 12 and 48 hours in 150- 
cc. quantities of buffer mixtures of 0.01 M phosphoric acid and 0.01 M sodium hydroxide. 
The buffer mixtures replaced at 12, 24, and 48 hours. See table 2. 
