Mar. 8, 1924 
Acidity Changes during the Growth of Wheat 
735 
which bring about daily fluctuations in acidity, but these variations are 
insignificant in comparison with the changes correlated with the chang¬ 
ing stage of development of the plant, so that the major trends in the 
acidity curves persist clearly under all conditions. 
Stunted, slow-growing plants, such as those of Kanred in a warm green¬ 
house, are characterized by an extremely high titratable-acid and hydro¬ 
gen-ion concentration and may not have the intermediate period of low 
acidity. Also, infection by mildew, when severe enough to visibly affect 
the vigor of the plant, results in an abnormally high acidity. 
The validity of varietal comparisons based on acidity measurements 
may be open to question unless the plants are at the same stage of devel¬ 
opment as well as of the same age, equally vigorous, and subjected 
throughout their development to the same environmental conditions. 
Varietal resistance to stem rust is not related at any stage of develop¬ 
ment to titratable-acid or hydrogen-ion concentration. 
High acidity of the juice does not hinder attacks of the stem-rust 
organism, for investigators have found that the wheat plant is as sus¬ 
ceptible during the heading and flowering stages as it is during the 
earlier periods of low acidity. Conversely, low acidity does not pre¬ 
dispose to the disease, since the plant is no more liable to infection 
during the period of lowest acidity than it is during the earlier and 
later stages. Moreover, resistant varieties pass through the period of 
low acid concentration at the same stage as do the susceptible ones and 
no breakdown in their resistance at this time has been reported. 
LITERATURE CITED 
(1) Farrer, W. 
1898. THE MAKING AND IMPROVEMENT OF WHEATS FOR AUSTRALIAN CON¬ 
DITIONS. In Agr. Gaz. N. S. Wales, v. 9, p. 131-168. 
(2) Freeman, E. M., and Johnson, E. C. 
1911. THE RUSTS OF GRAINS IN THE UNITED STATES. U. S. Dept. Agr. Bur. 
Plant Indus. Bui. 216, 87 p., illus. 
(3) Gassner, G. 
1915. untersuchungen uber die abhangigkeit des auftretens der 
getreideroste vom entwicklungszustand der nahrpflanze und 
von AussEREN faktorEn. In Centbl. Bakt., Abt. 2, Bd. 44, p. 512- 
617. 
(4) Hurd, Annie May. 
1923. hydrogen-ion concentration and varietal resistance of wheat 
to stem rust and other diseases. In Jour. Agr. Research, v. 23, 
p. 373-386. Literature cited, p. 384-386. 
(5) Melchers, L. E., and Parker, J. H. 
1922. RUST RESISTANCE IN WINTER-WHEAT VARIETIES. U. S. Dept. Agr. Bui. 
1046, 32 p., illus. Literature cited, p. 30-32. 
(6) Peltier, G. L. 
1923. A STUDY OF THE ENVIRONMENTAL CONDITIONS INFLUENCING THE DE¬ 
VELOPMENT OF STEM RUST IN THE ABSENCE OF AN ALTERNATE HOST. 
II. INFECTION STUDIES WITH PUCCINIA GRAMINIS TRITICI FORM III AND 
form ix. Nebr. Agr. Exp. Sta. Research Bui. 25, 52 p., illus. 
(7) Stakman, E. C., and Levine, M. N. 
1922. THE DETERMINATION OF BIOLOGIC FORMS OF PUCCINIA GRAMINIS ON 
triticum spp. Minn. Agr. Exp. Sta. Tech. Bui. 8, 10 p., illus. 
Literature cited, p. 10. 
(8) - and PiEMEiSEL, F. J. 
1917. BIOLOGIC FORMS OF PUCCINIA GRAMINIS ON CEREALS AND GRASSES. In 
Jour. Agr. Research, v. 10, p. 429-496, illus. Literature cited, p. 
493 - 495 * 
