390 
Journal of Agricultural Research 
Vol. XXXI, No. 4 
duced by che root tips. In the experiments in which hydrogen was 
bubbled continuously through the liquid in which the soy-bean root 
tips were placed, the final reaction reached from the acid side (Table 
III) was never more than P H 6.44. If the root tips were allowed to 
stand undisturbed in the liquid, the P H measured colorimetrically 
quickly approached 5.9, at which point it remained constant. If the 
reaction of the solution were then determined electrometrically, it was 
found to be near P H 6.7. This is illustrated by the following experi¬ 
ment. 
Sixty root tips of Virginia soy beans, totaling about 3.2 gms., were 
placed in 25 c. c. of 0.001 M. potassium phosphates in a 150 c. c. 
beaker and allowed to stand quietly. The reactions of the solutions 
were read colorimetrically. Within 10 minutes a solution of original 
P H 5.6. had changed to P H 5.9, and it remained unchanged in re¬ 
action for 90 minutes, during which time determinations of the 
hydrogen-ion concentration were made colorimetrically at intervals. 
Alter 60 minutes a solution of original P H 6.1 had changed to P H 5.9. 
After 90 minutes the reactions of the two solutions, which were 
P H 5.9 colorimetrically, were determined electrometrically. The 
values were P H 6.72 and 6.85, respectively. The solutions were re¬ 
moved from the electrode vessels and the reaction measured colori¬ 
metrically. The results were P H 6.7 and 6.9, respectively. 
These results were evidently due to the carbon dioxide produced 
by the respiration of the root tips. Standing quietly in the solutions 
in the beakers, carbon dioxide given off by the root tips accumulated 
in the solutions and kept the reaction near P H 5.9. This point, as 
indicated by the majority of the data in Table III, is acid to what the 
writers have called the isoelectric point. The absorption of the 
phosphate ion therefore continued. When the electrometric deter¬ 
mination was made, the carbon dioxide in the solution was swept out 
by the hydrogen, and the reaction in the absence of the carbon 
dioxide was found to be P H 6.7 to 6.9. If the carbon dioxide had not 
been present, the reaction would probably have slowly changed in 
both solutions to approximately P^ 6.4, at which point the change 
would have ceased. Evidently acidity produced by carbonic acid 
affects the relative amounts oi cations and anions absorbed, just as 
does the acidity produced by phosphoric acid. 
MYCELIAL MATS OF GIBBERELLA SAUBINETII 
This fungus, as well as the two others described later in this paper, 
was grown on the mineral nutrient solution used by one of the 
writers (8) with a total concentration of 0.066 M. monobasic and 
dibasic potassium phosphate and an initial P H of 5.0. The mycelial 
mats were removed from the nutrient solutions and thoroughly 
washed with 0.2 M. cane-sugar solution or redistilled water. The 
excess liquid was pressed out of the mats, which were placed in the 
dilute buffer mixtures, where readings were taken, with the hydrogen 
bubbling continuously until equilibrium was reached. 
This strain of Gibberella saubinetii was one isolated by B. B. 
Branstetter from com. The results obtained with this organism 
are summarized in Table IV, and Figure 1 shows curves with the 
P H of the solutions on the ordinate and the time on the abscissa. 
