730 
Journal of Agricultural Research voi. xxvii, No. 10 
seedling stage and in the steady extreme rise thereafter, coincident with 
the appearance of symptoms of stunted vegetative growth. The volume 
of N/20 NaOH required to neutralize a 10 cc. sample of juice increased 
from 8 to 18.8 cc. in seven weeks. Incidentally, the juice of these 
plants reached the hydrogen-ion concentration represented by P H 5.39, 
which is extraordinarily high for wheat. 
hydrogen-ion concentration in relation to stage of development 
The P H values of the samples, the titratable-acid concentrations of 
which are given in figures 1 to 3, inclusive, are plotted in figure 5 to show 
the extent to which the hydrogen-ion concentration of the juice changes 
with the development of die plant. 
/At 
Fig. 5. —The hydrogen-ion concentration of wheat juice from the seedling to the late-flowering stage. 
The plants erf Series C were cut in the forenoon at some periods and in the afternoon at others as indicated. 
From these curves it appears that the regular decrease in concentra¬ 
tion of titratable acid which has been shown to characterize the juice of 
wheat seedlings from the age of 2 to about 6 weeks is not accompanied 
by a correspondingly marked decrease in concentration of hydrogen ions. 
During the greater part of the plants' development the curves show rela¬ 
tively small and irregular variations which indicate the effects of daily 
fluctuations in the environment. During the preripening stage, charac¬ 
terized by an increasing titratable-acid concentration, there is a regular 
upward trend in each hydrogen-ion curve also, indicating that an in¬ 
creasing concentration of hydrogen ions parallels the increase in concen¬ 
tration of titratable acid. 
The effects of minor daily fluctuations in environmental factors appear 
in many of the curves. The existence of these effects is made evident 
by the conspicuous parallelisms in the courses of certain curves, the cor¬ 
responding points on which were obtained on the same days throughout. 
This does not mean that the varieties represented by such curves are 
more nearly like each other physiologically than like any others of the 
group, but simply that since the plants of each were always cut at the 
