386 
Journal of Agricultural Research 
Vol. XXXI, No. 4 
point, it should change toward greater alkalinity the reaction of 
solutions that are more acid than the isoelectric point, and vice versa. 
The equilibrium point reached would depend on the relative quantities 
of tissue and buffer mixture, the reactive power of the tissue, and the 
strength of the buffer mixture. If an ampholyte were present in 
excess, the equilibrium point would correspond with the isoelectric 
point. If it were deficient, the equilibrium point would be more acid 
or more alkaline than the isoelectric point, depending upon which 
side the initial reaction lay. 
The tissues used were potato-tuber tissue, root tips of Virginia soy 
beans, and the mycelial mats of three fungi: Fusarium lycopersici , 
Gibberella saubinetii , and Fusarium oxysporum. 
The reaction of the solutions was measured electrometrically with 
the saturated calomel electrode, a modified Hildebrand type of bubbling 
hydrogen electrode, a Leeds-Northrup type K potentiometer, and 
type It galvanometer. The hydrogen electrode was a straight piece 
of platinum wire suitably coated with platinum black. A siphon 
bridge was used with a curved capillary for making contact with the 
solution in the electrode vessel, and with a wooden plug in the end 
in the saturated potassium chloride solution to minimize diffusion. 
When the wooden plug was placed in the end of the siphon in contact 
with the liquid in the electrode vessel, disturbances were produced 
which interfered with the determination of the E. M. F. The bridge 
was left in contact with the liquid in the electrode vessel during the 
entire time of the experiment. Some diffusion of the saturated 
potassium-chloride solution into the electrode vessel probably 
occurred, and, if it did, this may have been a disturbing factor in 
the experiments. The wooden plug and capillary, however, pre¬ 
vented much diffusion. 
All determinations were made at temperatures which varied 
between 23.5° and 26.0° C. The light from an electric lamp shone 
on the tissue during the experiments. 
EXPERIMENTAL DATA 
POTATO-TUBER TISSUE 
The potato-tuber tissue was prepared as described earlier (-5), in 
disks about 1 cm. in diameter and 1 mm. thick. About 4 gms. were 
placed in 10 c. c. of 0.001 M. potassium dihydrogen phosphate, the 
reaction of which had been adjusted to the desired P H by the addition 
of 0.001 M. potassium hydroxide. The electrode was surrounded by a 
basketwork of platinum to keep the potato disks from touching it. 
The electrode vessel consisted of the lower third of a 100 c. c. gradu¬ 
ated cylinder. With the hydrogen bubbling continuously through 
the solution, the E.M.F. was read at intervals until an equilibrium 
point was reached. The tissue was then removed from the solution) 
and the E.M.F. determined. This was considered the final reading. 
In somb cases a fresh lot of tissue was added to the solution in order 
to make certain that the equilibrium point reached was not due to 
the saturation of the tissue with the particular ion concerned. 
The data for a typical pair of experiments performed on the same 
day are given in Table I. In experiment 12, a solution of P H 6.32 
became more alkaline, reaching a final equilibrium point of P ? 6.44. 
In experiment 13, a solution of P H 6.69 became more acid, reaching an 
