May, 1922] TOTTINGHAM AND RANKIN NUTRIENT SOLUTIONS 
in Livingston and Tottingham's solution R8C1 at o.i the usual concentra- 
tion and adjusted to pH 7.5. The plants grew in the solutions from June 
7 to June 14. During this period the cHmatic measurements were as follows : 
Mean daily evaporation from standard spherical white atmometer, 16.6 cc. 
Mean daily evaporation from standard spherical black atmometer, 23.3 cc. 
Ratio of black to white instrument, 1.40. 
The growth data of this test also appear in table 4. 
When dismounted, the appearance of the tops grown in the solution 
having a pH value of 7.5 was superior to that of plants grown at pH 6.4. 
The latter were developing yellow color in the leaves. The combined 
tests indicate that pH 7.5 excels pH 6.4 on the basis of elongation of the 
plants, but that the lower pH leads to greater production of dry matter. 
The latter result compares favorably with previous results from solutions 
intermittently renewed, which also have shown a favorable effect of slight 
acidity of the culture solution as measured by production of dry matter. 
As suggested by Meir and Halsted (12), however, solutions of relatively 
high hydrogen-ion concentration may be efficient on account of their 
correspondingly high phosphate content and resulting buffer capacity, 
rather than because of acidity per se. They may also favor availability of 
iron, as suggested by McCall and Haig (11). 
Conclusions 
The optimal nutrient conditions, as regards pH values, appear to differ 
as between the germination phase and the later growth of wheat. Hy- 
drogen-ion concentrations which are endured by the wheat plant in in- 
termittently renewed solutions become unendurable when the solution is 
continuously renewed. Certain pH values which restrict the elongation 
of stem and root in wheat appear to favor the production of dry matter 
in these organs. 
The above noted relations enhance the importance of specification of 
the standards by which nutrient efficiency is to be measured. They also 
suggest the advisability of employing the method of continuous renewal 
of the nutrient solution, or equivalent procedure, for more rigid control of 
experimental conditions. Obviously, in its relation to agricultural practice, 
this suggestion involves consideration of the extent to which field crops 
modify the composition of the soil solution. Inasmuch as changes of 
concentration of the water-soluble constituents have been found to follow 
cropping of the soil (Stewart, 18; Burd, i), there appears to be a consider- 
able degree of practicability in the original plan of intermittent renewal of 
nutrient solutions. 
Department of Agricultural Chemistry, 
University of Wisconsin 
