726 
Journal of Agricultural Research voi. xxvii, no. io 
RESULTS 
titratable-acid concentration in relation to stage of 
DEVELOPMENT 
As might be expected in view of the high buffer content of plant juices, 
more striking changes with the plant’s development were found to occur 
in the concentration of titratable acid than in the concentration of free 
hydrogen ions in the juices from these plants. The titration results 
therefore will be presented first, though the hydrogen-ion determinations 
are not without interest and will be given in the section following. 
Seed of the first series (A) of plants to be grown to maturity was sown 
on November i, 1922, 4 in a greenhouse bench containing limed sandy- 
loam soil of slightly alkaline reaction (P H 7.2). Acidity determinations 
were made on sap of each variety at frequent intervals from the time the 
plants were about 3 inches high until they were in the flowering stage at 
the age of approximately six months. After that time the measurements 
had to be discontinued because the plants became so dry that the requisite 
quantity of juice could not be expressed. The course of the changes in 
the titratable acidity of all six varieties during this period is shown in 
figure 1. The age of the plants was always reckoned from the date of 
sowing. Owing to the diurnal acidity changes reported to occur in many 
Fig. i.—T he titratable-acid concentration of wheat juice from plants of Series A, from the seedling to 
the late-flowering stage. (Greenhouse, Nov. i, 1922, to Apr. 3, 1923.) 
plants, only values obtained from plants cut about i o’clock in the 
afternoon were used in order to insure direct comparability of all points 
on the curves. 
The first experiment was repeated with portions of the same seed lots 
sown three weeks later on another bench of the same greenhouse. The 
additional precaution was taken of making smaller plots and duplicating 
the sowing of each variety in order to lessen the chance of error from 
inequalities in the light, temperature, or water supply along the bench. 
The plants of this series (B) were somewhat more vigorous than those of 
Series A because of more favorable temperature and moisture conditions, 
but their rate of development was practically the same. To eliminate 
the effects of cutting at different times of the day, only values obtained 
for plants cut at 9 o’clock in the morning are plotted in figure 2. 
4 Seed for Series A and B was obtained by J. H. Martin from the Agricultural Experiment Stations at 
Dickinson, N. Dak. (Kota, C. I. 5878, Preston, C. I. 3081, Pentad, C. I. 3322, Marquis, C. I. 3641), Akron, 
Colo. (Khapli, C. I. 4013) and Moro, Oreg., (Eittle Club, C. 1 . 4066). 
