Aug. 15,1925 
Studies on Isoelectric Points for Plant Tissue 
389 
tuber tissue. They show that potato-tuber tissue affects the reaction 
of 0.001 M. potassium phosphates much the same as would an am¬ 
photeric colloid with a definite isoelectric point. The so-called 
isoelectric point found in the present experiments is more alkaline 
than that found in the earlier experiments. A more dilute buffer 
mixture, and the potassium phosphates instead of the sodium phos¬ 
phates, were used in the present experiments. It is interesting to 
note that Stiles and Jprgensen (10) found that potato-tuber tissue 
neutralized both dilute hydrochloric acid and dilute potassium 
hydroxide. 
SOY-BEAN ROOT TIPS 
Virginia soy beans were germinated between filter papers in pans, 
and a centimeter or two or the root tips was cut oft. From 24 to 
60 such root tips were placed in 10 c. c. of the 0.001 M. potassium 
pHosphates. The electrode used was of the same type as that used 
m the experiments with potato, but it was not protected with the 
platinum basketwork, as the root tips, being smaller, were less likely 
to strike it. 
The results of the experiments with soy-bean root tips are sum¬ 
marized in Table III. The results are much less uniform than with 
potato. Solutions of initial P H of 6.68, 6.69, and 6.78 were made 
more acid. Solutions of initial P H of 5.82 and 6.20 were made more 
alkaline. In three cases, solutions of P H 6.32 or 6.33 became more 
alkaline, and in four cases more acid. The lowest Sorensen unit 
reached from the alkaline side was P H 5.89, and the highest from the 
acid side was P H 6.44. Considering experiments performed on a 
single day, such as 1 and 2, 5 and 6, and 9 and 10, the root tips affected 
the solutions as an ampholyte would be expected to affect them. 
The majority of the experiments indicate that the isoelectric point 
for soy-bean root tips lies in the vicinity of P H 6.20 to 6.44. 
Table III .—Summary of experiments with Virginia soy-bean root tips. Tissue in 
each case placed in 10 c. c. of 0.001 M . potassium phosphates and reaction deter¬ 
mined until equilibrium was reached 
Experi¬ 
ment 
No. 
Time 
in days 
from 
begin¬ 
ning of 
germi¬ 
nation 
Initial 
Ph 
Final 
Ph 
Time 
in min¬ 
utes 
Weight 
of tis¬ 
sue in 
grams 
Experi¬ 
ment 
No. 
Time 
in days 
from 
begin¬ 
ning of 
germi¬ 
nation 
1 
i 
l 
Initial 
Ph 
Final 
Ph 
Time 
in min¬ 
utes 
Weight 
of tis¬ 
sue in 
grams 
1 _. 
7 
6.20 
6.43 
45,25 
2X0.7 
6. 
7 
6.32 
6.19 
100 
1.5 
2 
7 
6.78 
6.42 
34, 54, 
4X0.7 
7_ 
5 
6.32 
6.38 
116 
1. 5 
38,108 
8. 
5 
5.82 
6.18 
112 
1.5 
3 
4 
6.32 
6.34 
127 
0.8 
9_ 
6 
6.33 
6.44 
93 
1.3 
4_ 
5 
6.68 
6.19 
180,49 
2X0.9 
10_ 
6 
6.69 
6.49 
150,18 
2X1.3 
5. 
7 
5.82 
6.13 
39, 25, 
4X1.5 
IK- _ 
7 
6.33 
5.96 
191 
1.3 
20,23 
12_<— 
8 
6.32 
5.89 
164 
2.3 
The writers do not know why the results of successive experiments 
with the soy-bean root tips are not duplicates. One factor may be the 
age of the root tips; another may be the fact that meristematic tissue 
was being dealt with as well as partially or completely differentiated 
tissue, the proportions varying in the different lots of root tips. 
Some extremely interesting observations were made on the effect 
of the acidity due to carbon dioxide on the changes in reaction pro- 
