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Journal of Agricultural Research voi. xxvn, No. 10 
The major trends in the curves of figure 3 are essentially the same as 
those of figures 1 and 2 and therefore establish the fact that the acidity 
of the wheat plant undergoes certain regular changes during develop¬ 
ment from the seedling stage to maturity and that these changes are not 
environmental effects but the results of inherent physiological character¬ 
istics. There is a progressive decrease in acid during the early-seedling 
stage of the plants of all varieties, with the lowest concentration reached 
between the ages of 4 and 6 weeks. Then there follows an intermediate 
period, continuing up to the visible approach of maturity, during which 
no regular trend is discernible in the curves but only irregular fluctuations. 
These fluctuations are obviously correlated with variations in the daily 
environment, as they differ in each series and are often conspicuously 
parallel for those varieties which were always cut at the same time. 
During the stage immediately preceding maturation when the culms turn 
yellow, the lower leaves dry and turn yellow, and head formation begins, 
the curves turn rather sharply upward, and indicate a steadily increasing 
acidity. By the time the heads have reached the soft-dough stage, the 
acid concentration is as great or greater than the maximum found in the 
seedling stage. 
In each series the final upward slopes of the acidity curves were cor¬ 
related with the drying out of the culms and leaves, the acidity remain¬ 
ing low as long as the plants remained succulent. In other words, the 
acid concentration during the period of head and flower formation is 
apparently determined by the loss of water from the tissues. For in¬ 
stance, in Series A and B the heads did not appear in the boot until the 
plants were partially dry, yet the acidity had begun to rise while the 
plants were still in the shooting stage. In Series C, on the other hand, 
in which development was more rapid and the head appeared in the boot 
while the plants were still vigorous and juicy, the acidity remained low 
during the period of head formation and did not rise until the flowering 
stage when the plants began to dry. 
Incidentally, Khapli was usually one of the first to head and dry, 
while the development of Little Club was slower and its maturation more 
delayed. It follows, therefore, that when this difference in rate of 
development and drying exists toward the end of the growing period, 
Khapli will be found to be the more acid in each comparison of values 
obtained on the same date. In other words, not age alone but also the 
stage of development determines the acidity of the plants, and this fact 
must be taken into account in comparisons between varieties which do 
not mature equally rapidly. 
The major trends in the acidity curves are substantially alike in all 
three series and represent tendencies inherent within the plant, yet 
environmental factors have left their impress. Higher soil acidity 
possibly was responsible for the fact that the seedlings of Series C were 
very much more acid at first than were those of the same age in the 
other two series. Also, environmental conditions, by determining the 
rate of development, determined both the duration of the interval 
elapsing before the beginning of the final ascending portion of each curve 
and the rate at which the acidity increased during the preripening 
period. 
The foregoing data and discussion relate to healthy plants. When 
normal growth Ts prevented by an unfavorable environment, such as 
that which obtains for a winter wheat grown in the greenhouse during 
the warm spring months, the acidity curve differs from those given in 
