Oct., 1923] ROBBINS-ISOELECTRIC POINT FOR PLANT TISSUE 
421 
reaction is not noted to the same extent or regularity in buffer mixtures of 
pH 5.8 and above. The increase in weight in this series was decidedly 
greater than with the stronger salts used in the first experiment. There 
was also a small continued increase at the end of 24 hours instead of the 
loss noted before. At the end of 48 hours, however, the potato in all solu¬ 
tions showed a decrease in weight below the maximum attained. This 
loss was again greatest at the acid end and least in the solution of pH 5.4, 
being but 0.03 g. there, while it was from 0.11 to 0.68 g. in the other buffer 
mixtures. The potato tissue in this solution again remained almost constant 
in its gain at the 12-, 24-, and 48-hour weighings. 
If we plot the gain or loss in weight against the average pH of the 
solutions and draw a smooth curve through the points secured, as has been 
Table i . The molecular concentration of the two constituents of the buffer mixtures used in 
experiments on water absorption 
Sol. No. 
Phthalate 
Citrate I 
Citrate II 
Phosphoric Acid 
KH 
Phthalate 
NaOH 
Na 
Citrate 
NaOH 
Na 
Citrate 
NaOH 
H3PO4 
NaOH 
mol. 
mol. 
mol. 
mol. 
mol. 
mol. 
mol. 
mol. 
I 
O.OI 
0.00008 
0.00980 
0.00020 
0.00200 
0.00000 
0.0714 
0.0285 
2 
O.OI 
0.00150 
O.OO950 
0.00050 
O.OOI96 
0.00004 
0.0510 
0.0488 
3 
O.OI 
0.00354 
0.00900 
0.00100 
0.00180 
0.00020 
0.0500 
0.0500 
4 
O.OI 
0.00599 
0.00800 
0.00200 
0.00160 
0.00040 
0.0495 
0.0504 
5 
O.OI 
0.00797 
0.00700 
0.00300 
O.OOI4O 
0.00060 
0.0490 
0.0509 
6 
O.OI 
0.00860 
0.00600 
0.00400 
0.00120 
0.00080 
0.0481 
0.0519 
7 
O.OI 
0.00870 
O.OO575 
0.00425 
0.00115 
0.00085 
0.0471 
0.0528 
8 
O.OI 
0.00890 
0.00550 
0.00450 
0.00110 
0.00090 
0.0454 
0.0545 
9 
O.OI 
0.00920 
O.OO525 
0.00475 
0.00105 
0.00095 
0.0417 
0.0583 
10 
11 
O.OI 
0.00940 
O.OO510 
0.00490 
0.00102 
0.00098 
0.0384 
0.0333 
0.0615 
0.0666 
Table 2. The gain in weight of 10 g. of potato-tuber tissue in 12 , 24, and 48 hours in 150-cc. 
quantities of buffer mixtures of 0.01 M H3PO4 and 0.01 M NaOH, the buffer 
mixtures being replaced with afresh supply at each weighing 
Sol. No. 
Initial pH 
pH at 
End of 
12 Hrs. 
pH at 
End of 
24 Hrs. 
pH at 
End of 
48 Hrs. 
Gain or 
Loss, 
12 Hrs. 
Gain or 
Loss, 
24 Hrs. 
Gain or 
Loss, 
48 Hrs. 
I 
2.0 
2.0 
2.0 
2.0 
g- 
I. 4 Irt .036 
g- 
0.I4dr.02 
g- 
— 0.72dr.06 
2 
3-5 
3-5 
3-5 
3-5 
2.33 ±.046 
2.39dr.06 
2.05 dr.02 
3 
4.1 
4-5 
4-5 
4-3 
2.02 ±.08 
2.36dr.09 
2.01 dr.02 
4 
47 
4-9 
4.8 
4.9 
2.i8d=.036 
2.21 dr.OI 
I. 94 rb .04 
5 
54 
5-6 
5-5 
5-6 
2.25 i.01 
2.3ldr.03 
2.29 dr.OI 
6 
5-8 
5-7 
575 
5-8 
i.66=L.07 
1.88 dr.05 
1 .51 dr.OO9 
7 
6.0 
6.1 
6.1 
6.1 
2.25 db.04 
2.38 dr.OI 
2 .IOrb .04 
8 
6.2 
6,2 
6.4 
6.2 
2.3Od=.02 
2.3I dr.04 
2.l6rb.04 
9 
6.6 
6.7 
6.9 
6.8 
I. 70 =t .05 
1.99 dr .13 
I; 88 dr. 04 
10 
7.0 
7-1 
7 -i 
7 -i 
i.83±.o6 
2.06 zb.12 
I.9I rb.03 
11 
8.0 
8.0 
8.0 
8.0 
1.82 ±.03 
2.09 dr.08 
I. 94 rb .04 
12 
9.0 
9.0 
9.0 
9.0 
2.23 dr .02 
2.66zb.05 
1.47 dr.006 
Dist. 
H 2 0 
