432 
AMERICAN JOURNAL OF BOTANY 
[Vol. io. 
potato, I x 15 mm., were placed in tumblers in 200-cc. quantities of the 
buffer mixtures of different H-ion concentration. After periods varying 
from 1.5 to 5 hours, two discs from each solution were removed to a Syracuse 
watch crystal. They were covered with the dye, and after a few seconds’ 
to 15 minutes’ staining were removed, washed with redistilled water, and 
examined for relative intensity of staining. In some cases, after staining 
the pieces were washed with the original buffer mixtures. Water redistilled 
from alkaline and acid permanganate was used throughout in the prepara¬ 
tion of the buffer mixtures and the solutions of the dyes. 
Three sets of buffer mixtures were used, two composed of H 3 P 0 4 and 
NaOH and one of secondary sodium citrate and NaOH. Most of the 
experiments were performed using solutions obtained by mixing 0.1 M 
H3PO4 and 0.1 M NaOH and diluting 50 times. This was equivalent to 
mixing 0.002 M H3PO4 and 0.002 M NaOH. The original pH of these 
solutions as well as the pH of the solutions after 3 and 5 hours’ contact with 
the potato are given in table 7. A set of buffer mixtures was also prepared 
by mixing 0.1 M H3PO4 and 0.1 M NaOH and diluting 5 times. This was 
equivalent to mixing 0.02 M H 3 P 0 4 and 0.02 M NaOH. The initial pH of 
the solutions used in this set and the pH of the solutions after standing in 
contact with the potato are also given in table 7. Buffer mixtures obtained 
by mixing 0.1 M secondary sodium citrate and 0.1 M NaOH and diluting 50 
times were also used. This was equivalent to mixing 0.002 M secondary 
sodium citrate and 0.002 M sodium hydroxide. The original pH values 
of these buffer mixtures and the pH of the solutions after contact with the 
potato are given in table 7. 
A consideration of the data there given confirms what was previously 
observed in the experiments on water absorption. The presence of the 
potato changed the pH of the solutions on the acid side of pH 5.8 toward 
greater alkalinity and on the alkaline side of 6.1 or 6.2 toward greater 
acidity. 
The acid dyes used were orange G, eosin, Martius yellow, and acid 
fuchsin. The basic dyes were methylene blue, safranin, malachite green, 
and crystal violet. 
Excellent results were secured with the acid dyes, eosin and Martius 
yellow, the potato responding as though its isoelectric point were located 
somewhat above pH 6.0. 
The eosin was used at a concentration of 1-500 and the periods of staining 
varied from 3 to 10 minutes. To cite specific experiments: 
Twenty slices of potato were soaked in the buffer solutions composed of 
0.002 M H3PO4 and 0.002 M NaOH for 2 hours. Two slices from each 
buffer mixture were removed and stained in Syracuse watch crystals with 
1-500 eosin for 3 minutes. When removed from the stain little difference 
in color was noted. They were washed in the watch crystals with 3 changes 
of redistilled water. The potato from solution 2, pH 2.85, was very red; 
