Aug. 15, 1925 
Studies on Isoelectric Points for Plant Tissue 
395 
In the curves of Figure 3, a peculiarity of the results of some of 
the experiments (3, 4, 5, and 6) with this fungus is evident. In all 
four of these experiments the initial effect of the mycelium was to 
produce an alkalinity greater than the final equilibrium point, form¬ 
ing humps on the curves. 
Table VI .—Summary of results with mycelium of Fusarium oxysporum . Tissue 
in each case placed in the solution indicated , and reaction measured until equi¬ 
librium was reached 
Experi¬ 
ment No. 
Weight 
of 
mycelium 
Age of 
mycelium 
Kind of buffer solution used 
Quantity 
of buffer., 
solution 
used 
. Initial 
Ph 
Final 
Ph 
Time 
required 
to reach 
equilib: 
rium 
1_ 
Grams 
1.03 
Days 
17 
0.01 M. KTT phthalate_ 
C.c. 
10 
4.02 
4.70 
Minutes 
40 
2___ 
1.13 
17 
0.01 M. KH phthalate . . 
10 
4.04 
4.63 
38 
3.. 
3.17 
9 
0.001 M. Na phosphates ___ 
50 
3.80 
4.64 
52 
4. 
0.50 
15 
0.0005 M. Na phosphates. 
25 
4.73 
4.94 
19 
5 .: 
0.90 
17 
0.001 M. KH phthalate, KOH. 
10 
5.06 
4 71 
166 
6_ 
T.46 
9 
0.001 M. Na phosphates 
10 
5.70 
5.195 
54 
7_ 
> 1.39 
9 
0.001 M. Na phosphates 
10 
7.36 
4.92 
101 
8__ 
•- 2.282 
11 
0.001 M. Na phosphates... 
50 
6.94 
5.94 
58 
9_ 
1.50 
11 
0.001 M. Na phosphates_ 
10 
7.10 
6.21 
15 
10„._. 
0.47 
11 
0.001 M. Na phosphates_ 
5 
7.10 
6.31 
12 
DISCUSSION 
The experiments reported here show that under the conditions of 
these experiments, plant tissue acts much like an ampholyte with a 
definite isoelectric point. For potato-tuber tissue this point is near 
P H 6.4, for the mycelium of OiboereTla saubinetii near P H 6.2, for that 
of Fusarium lycopersici near P H 5.5, and for Fusarium oxysporum 
near P H 4.9. For the root tips of soy beans it is in the neighborhood 
of P H 6.2 to 6.4, but further work is necessary to define it more 
exactly, if possible. v 
The decided difference in the so-called isoelectric points for these 
three closely related fungi suggests the possibility of using this method 
or one similar to it as an aid m identification. 
The experiments also emphasize the importance of the acidity 
produced by carbonic acid. If the writers’ interpretation of the 
experiments is correct, the accumulation of this acia can profoundly 
affect the absorption of ions by the cell, and probably, also, other 
physiological processes which depend upon reaction with the iso¬ 
electric point as the critical one. Most of the isoelectric points 
reported here are in the zone in which carbonic acid can affect the 
reaction. This suggests the importance of considering the carbon- 
dioxide content of the cell contents when the hydrogen-ion concen¬ 
tration of plant tissue is determined. Apparently most determina¬ 
tions of the hydrogen-ion concentration of plant tissues are now 
made on the extracted sap with no attention paid to the carbon- 
dioxide content of the juice. Yet the acidity due to carbon dioxide 
may be as important in plant juices as in the blood of animals. Its 
accumulation in the tissues of higher plants at night when the sto- 
mates are closed might throw the reaction across the isoelectric 
point or move it further away with possible profound physiological 
effects. 
The methods used in the experiments reported here need further 
refinement; and a study of the effect of various conditions, such as 
