Aug. 15,1925 
Studies on Isoelectric Points for Plant Tissue 
387 
equilibrium point of P H 6.46. In experiment 12 (Table I), the P H 
dropped from 6.32 to 6.26 2 minutes after the addition of the potato- 
tuber tissue, and at the end of 10 minutes it had reached a constant 
value of P„ 6.44. In experiment 13 (Table I), the addition of the 
potato had reduced the original P H of 6.69 to 6.31 at the end of 3 
minutes. At the end of 9 minutes, the Sorensen value of the solution 
had risen to 6.61 and then fallen slowly to 6.50 by the end of 60 min¬ 
utes. The addition of a fresh lot of potato-tuber tissue to this solu¬ 
tion caused a drop from P H 6.50 to P H 6.24 at the end of 6 minutes. 
At the end of 12 minutes after the fresh tissue was added the Sorensen 
value was 6.46, at which point it remained. 
Table I .-—Data for two typical experiments with 4-5 gms. of potato-tuber tissue 
placed in 10 c. c. of 0.001 M. potassium dihydrogen phosphate, the initial reaction 
of which was adjusted with 0.001 M. potassium hydroxide and the reaction meas¬ 
ured until equilibrium was reached 
Experiment 12 
Experiment 13 
Time in 
Ph 
Time in 
Ph 
minutes 
minutes 
0 
6.32 
0 
6.69 
2 
6.26 
3 
6.31 
10 
6.44 
9 
6.61 
18 
6.44 
14 
6.59 
24 
6.44 
26 
6.55 
30 
6.44 
45 
6.52 
(•) 
(•) 
57 
6.51 
37 
6.44 
70 
6.50 
39 
6.44 
( 6 ) 
( 6 ) 
76 
6.24 
82 
6.46 
91 
6.46 
102 
6.46 
(°) 
(•) 
106 
6.46 
109 
6.46 
a Tissue removed at this point. 
b Added 4.5 grams fresh potato at this point. 
The drop in Sorensen units a few minutes after the addition of the 
potato tissue to the solution, and the subsequent recovery, was noted 
m all the experiments summarized in Table II, except in experiments 
3, 4, and 5. In these three experiments the initial P H was 6.14 or less, 
and in all others 6.32 or greater. This immediate and temporary 
increase in acidity on the addition of the potato-tuber tissue to the 
dilute buffer mixtures is probably due to carbon dioxide introduced 
with the tissue and swept out in a few minutes by the constantly 
bubbling hydrogen. 
Table II .—Summary of experiments with potato-tuber tissue. Tissue placed in 
each case in 10 c. c. of 0.001 M. potassium phosphates, and reaction determined 
until equilibrium was reached 
Experi¬ 
ment 
No. 
Initial 
Ph 
Final 
Ph 
Time in 
minutes 
Amount 
potato in 
grams 
- 1 
1 
?s| 
-*• P. 
Initial 
Ph 
Final 
Ph 
Time in 
minutes 
Amount 
potato in 
grams 
1. 
6. 54 
6. 39 
145 
4.1 
8_ 
6. 67 
6.46 
63 
4.3 
2 
6.32 
6. 02 
119 
4.1 
9_ 
6.33 
6.16 
165 
4.5 
3 
5.85 
6.20 
72 
4.0 
10_ 
6.33 
6. 37 
33 
4. 5 
4 _ 
6.10 
6. 43 
116 
4.4 
11_ 
6. 69 
6.38 
90,31 
2X4. 5 
5_ 
6.14 
6. 43 
99 
4.3 
12_ 
6. 32 
6.44 
30 
4. 5 
6 _ 
6. 68 
6.45 
54 
4.3 
13.. 
6.99 
6. 46 
70,30 
2X4.5 
7. 
6. 32 
6.44 
55 
4.3 
