73 2 Journal of Agricultural Research voi.xxvii.No.io 
ing stage, is his observation that very young seedlings are sometimes 
more susceptible than older plants though not so readily infected as those 
which have passed the flowering stage. Thus it would appear that, if 
there be any correlation, the degree of infection of a susceptible variety 
varies directly rather than inversely with the acid concentration. How¬ 
ever, these observations may be wholly unrelated and the apparent corre¬ 
lation accidental. At least it appears that the low acidity of the post¬ 
seedling period neither favors infection of susceptible varieties nor breaks 
down the resistance of resistant ones, nor does the high acidity of the 
older plants make susceptible varieties less liable to attack in the later 
stages of development. 
The significance of the acidity data for the disease-resistance problem 
may be considered also from the standpoint of varietal comparisons at 
each stage of the plant's development. Pentad and Kota are resistant 
to specialized forms to which Preston .and Marquis are susceptible. 
Khapli is resistant to all specialized forms known and Little Club is f 
susceptible to them all (7). Yet at no period in the growth of the plants 
from the age of two weeks to maturity was either the titratable-acid 
or the hydrogen-ion concentration of the expressed juice related to the 
degree of resistance or susceptibility characterizing the variety. Com¬ 
parisons are facilitated by the tabular arrangement in Tables I and II 
of the values from which the curves in figures 1,2,3, and 5 were plotted. 
Table I. —Titratable acidity of wheat at intervals from the seedling to the late-flowering 
stage, in cubic centimeters of N/20 sodium hydroxid required to neutralize 10 cc. of ex¬ 
pressed juice 
SERIES A a 
Age in weeks. 
Kota. 
Preston. 
Pentad. 
Marquis. 
Khapli. 
Little Club. 
2. 
7*4 
6. 4 
7 - 5 
7 * 1 
7 - 7 
7. 2 
6. 9 
7. I 
3. 
it 
7. 4 
6.8 
6. 2 
5-9 
5 * 5 
6. 0 
4 . . . . 
5-5 
5 - 7 
6. 2 
6. 4 
6. 0 
5 * 1 
5 - 5 
6. 7 
6. 
5*8 
5*'9 
5-8 
8. 
7 - ^ 
10. 
6.8 
7 - I 
5-9 
7. 2 
6. 1 
6.8 
7. 3 
12. 
6. 7 
6. 9 
6. 1 
7. 5 
6. 9 
16. 
6. 7 
7 . O 
7. O 
7 - 5 
8.7 
10. 1 
7. 2 
S.o 
20. 
10. 0 
10. 6 
8.6 
8. 2 
7*4 
22 . 
10. 6 
11. 2 
10. 0 
12. 0 
12.3 
26 
13. 0 
A o‘ V 
1 
<* Plant* cut at i p. m., the others at 9 a. m. 
