380 Journal of Agricultural Research v 0 i. xxin, no. 5 
ion concentration of potato juice showed no appreciable change upon the 
addition of a considerable volume of water. Harvey (13) reports that 
the addition of one volume of water changed the reaction of the juice of 
the tobacco plant by only 0.096 P H . In the present study it was found 
that, in germinator wheat seedlings a week old, the addition of an equal 
volume of water increased the P H value by 0.06, while the addition of two 
volumes raised it by 0.10. Greenhouse seedlings 2 to 7 weeks old 
were less highly buffered against dilution, since with them the addition 
of one volume of water produced an increase of 0.09 P H and two volumes, 
0.15 P H . No varietal differences in this respect were found, the de¬ 
terminations being made with the same result with sap from Kanred, 
Turkey, Khapli, and Little Club. Each figure given is an average of 
results obtained from six or more different samples. From these deter¬ 
minations we conclude that the small differences in concentration of the 
juice caused by excess moisture on the leaves, by methods of expressing, 
or by evaporation during handling do not produce appreciable errors in 
the hydrogen-ion measurements. 
In addition to the errors of manipulation affecting accuracy of measure¬ 
ments, those factors which influence the reaction of the cell sap in the 
growing plant must be considered before the validity of varietal compari¬ 
sons can be fully established. It was thought possible that the geograph¬ 
ical source of the seed may determine the plant's reactions to new 
environmental conditions in a sufficient degree to affect its acidity. 
Whenever possible, resistant varieties and susceptible varieties were 
obtained from the same experimental farm, but it was seldom possible to 
obtain Khapli and Little Club, the pair representing the most interesting 
extremes of resistance and susceptibility, from the same place. It seemed 
desirable, therefore, to determine the extent of agreement between the 
concentration of hydrogen-ions in seedlings from seed grown in different 
places. Below are given the P H values of germinator seedlings, a week 
old, of Khapli emmer from seed obtained from widely separated regions. 
Seed from 
Pullman, 
Wash., 1921. 
Seed from 
Dickinson, 
N. Dak., 1921. 
Seed from 
Akron, Colo., 
1921. 
5 - 92 
6.03 
5 - 94 
5 * 99 
6. 00 
S -96 
6. 00 
5 - 97 
5 - 94 
Three lots of Kanred, two of them from the same station, gave|the 
following results: 
Akron, Colo., 
X 92 Z. 
Manhattan, 
Kans., 1920. 
Manhattan, 
Kans., X92X. 
5-99 
6. 06 
6. 01 
5-93 
6. 02 
5-99 
5 - 94 
5-94 
5-98 
5 - 95 
6. 00 
5-98 
5-94 
5 - 99 
5-97 
