458 
Journal of Agricultural Research 
Vol. XXV, No. n 
any apparent disease symptoms; No. 1x3, 129, and 326 as stunted, with 
spotted or streaked, or prematurely dead leaves; No. 150, 350, and 507 
with various abnormalities of leaf and stalk, indicating susceptibility to 
disease; and No. 315 and 485 with a marked tendency to fall down. 
Four successive plantings of each of the 10 strains were made in green¬ 
houses and a fifth in an outdoor plot, on the grounds of the Department 
of Agriculture at Washington, D. C. Growth conditions in these plots 
were not equally favorable for com, hence the five series were strikingly 
different in vigor. 
The plants, grown to the age indicated in the different experiments, 
were cut about 2 inches from the ground, and after being carefully freed 
from dust and dirt, were ground in a food chopper. The juice was 
squeezed from the pulp by hand through clean muslin and its acidity 
determined immediately. In the earlier experiments, the juice from 
the whole top was expressed as one sample, but later, when the quantity 
of material permitted, the juice from the leaves and stalks was expressed 
separately. 
All hydrogen-ion determinations were made electrometrically. The 
major details of the method have been given in an earlier paper (ir). 
The titrations of total acidity also were made electrometrically, a uni¬ 
form procedure being followed in all cases. One-twentieth normal 
sodium-hydroxid solution was added, 1 cc. at a time, to a 10-cc. sample 
of undiluted juice by means of a burette, the tip of which was inserted 
through the cork in the electrode vessel. The P H values corresponding 
to the potential differences resulting from each successive addition of 
alkali to the sample were plotted against the corresponding quantities 
of sodium hydroxid. The quantity required to bring the hydrogen-ion 
concentration to P H 8.3, the turning point of phenolphthalein, was 
taken to represent the titratable acidity. 
In order to discover whether a relation existed between the acidity 
of the juice and its density, specific-gravity determinations were made 
for each sample in the later experiments. For these determinations the 
juice was filtered and refiltered through a folded filter until clear, pre¬ 
cautions being taken to prevent excessive evaporation. The density 
was determined by means of a small pycnometer in the form of a glass 
capsule with capillary intake and outlet tubes. The density is referred 
to water at the same temperature as that of the juice. 
RESULTS 
SERIES 1 
The first set of plants was grown in medium to fine sandy loam 4 with 
a neutral reaction (P H 7.0), in a greenhouse bench on which the soil 
was approximately 10 inches deep. By the sixth week, when the plants 
were cut, they had reached an average height of 50 cm. On the whole, 
the plants were normal and in good condition. Strains No. 113, 31, and 
326, however, were less vigorous than the rest. Either two or three 
plants, depending on their size, were cut for each sample. One set of 
determinations was made in the morning, and in order to compensate 
for any error from differences in the time of cutting and order of expres- 
4 1 am indebted to Mr. I,. A. Hurst, of the Office of Soil Fertility Investigations, Bureau of Plant In' 
dustry, for the technical descriptions of the soils used in this investigation. 
