734 
Journal of Agricultural Research voi. xxvii, No. io 
Table II.— Ph values of the expressed juice of wheat at intervals from the seedling to 
the late-flowering stage —Continued 
SERIES c 
Age in weeks. 
Kota. 
Preston. 
i 
j Pentad. 
Marquis. 
I 
| Khapli. 
1 
Little Club. 
2. 
a 6. 01 
a 6. 03 
a 5 - 9 6 
a 5 - 94 
I 
° 5. 98 
0 6. 04 
3 . 
a 6. 06 
a 5 - 99 
a 5. 96 
a 5 - 98 
“ 5 - 95 
a 6. 04 
5 - 9 2 
5 - 9 1 
5-89 
5 - 9 2 
5 - 9 6 
5 - 97 
a 6. 17 
a 6. 12 
a 6. 01 
a 6. 03 
a 6. 06 
a 6. 14 
6. 
5 - 93 
5 - 93 
5 - 98 
5 - 96 
5 - 93 
6. 01 
a 6. 03 
a tr qc 
c. 00 
r r»7 
8... 
0 
5- 8 9 
0 yo 
5- 82 
o* yy 
5 * 89 
j' y/ 
5 - 9 ° 
5 - 87 
5 - 84 
10. 
a 6. 13 
a 6 . 00 
5 - 9 i 
5 - 97 
5-93 
5 - 9 1 
12. 
5 - 94 
5 - 90 
5 - 94 
5 - 95 
a 5 - 98 
a 5 - 98 
13. 
5 - 96 
5 - 95 
6. 02 
5 - 84 
5 * 9 2 
14. 
a 6. 02 
° 6. 10 
0 6. 05 
a 6. 08 
0 5- 88 
a 5 - 97 
16. 
5 - 74 
s- 78 
a 5 - 85 
a 5- 82 
5- 60 
5 * 77 
18. 
5 - 67 
5 - 73 
a Plants cut at i p, ra., the others at 9 a. m. 
With the exception of the relatively high titratable-acid concentration 
of the young seedlings of Pentad in Series C, and the relatively high 
hydrogen-ion concentration of Khapli, up to the age of about io weeks, 
in Series A and B, the values in Tables I and II give no evidence of signifi¬ 
cant varietal differences, but rather* of surprisingly close agreements for 
varieties so unlike, both as to morphological type and susceptibility to 
disease. Since these few varietal differences do not occur in all three 
series they probably represent differences in the reaction of the variety 
to the particular environment and are without significance for the 
disease-resistance problem. The data as a whole confirm the earlier 
conclusion (4) that the hydrogen-ion concentration of wheat juice bears 
no relation to varietal resistance to stem rust, and permit the same 
conclusion with respect to titratable-acid concentration. 
CONCLUSIONS 
The titratable acidity of the juice of the wheat plant undergoes a 
regular sequence of changes during development from the seedling stage 
to maturity. There is a progressive decrease, sometimes to half the in¬ 
itial concentration, between the ages of two and about six weeks. This 
period is followed by a period of relatively low acidity, with minor 
fluctuations, extending up to the visible approach of maturity, at which 
time the acid concentration rises as the plants ripen and dry. The final 
value may be twice the highest seedling concentration and almost three 
times that of the least acid stage. 
The hydrogen-ion concentration of the juice of the wheat plant does 
not decrease appreciably between the ages of two and six weeks. It is 
greatly increased dining the preripening period and reaches a relatively 
high value at the flowering stage and later. 
This increasing acid concentration during the final stages of growth 
is correlated with the rate of drying rather than with head formation or 
kernel development. 
Both the titratable-acid and hydrogen-ion concentrations are influenced 
by environmental conditions which determine the rate of growth and 
