1920] 
DUGGAR—H-ION CONCENTRATION AND NUTRIENT SOLUTIONS 19 
With respect to corn it will be seen that the maximum yield 
occurs in culture Ac /10, although maximum root growth occurs 
in several B cultures. As between the different cultures in the 
A series the results are much the same as in the case of wheat 
except that the AcM culture with a combination of mono- and 
dibasic phosphate does not exhibit the benefit reported in the 
previous case. On the other hand, when one examines the data 
for dry weight quantities it will be found that maximum growth, 
as before, occurs in the B solution and in the culture to which 
solid calcium carbonate was added. Moreover, the next best 
growth is found in the addition of a slight amount of alkali to the 
B solution. 
Throughout this work it will be noticed that the variation in 
total growth amounts between the various cultures of peas, 
differing mainly in Pg, is not so marked as that shown by the 
other two plants used in these experiments. Again, there were 
considerable differences between different plants in the same 
culture (more marked, however, in the case of wheat), and this 
indicates beyond any doubt that the variability of the seed is a 
factor which may affect to a slight extent the regularity of the 
results. In any event, the maximum growth with peas in this 
series occurred when a small amount of sodium sulphate was 
added. The amount of growth in the unmodified A solution is 
considerable in spite of the high acidity, yet there appears to be 
a slight advantage in the addition of a small quantity of alkali, 
although the latter is rendered doubtful by a comparison of 
cultures ApO, Ap 1/, and Ap 3/. In solution A Canada field 
peas are apparently only slightly affected by changes in hydro- 
gen ion concentration up to the point of precipitation of the 
phosphate as the insoluble calcium salt. The curve, fig. 2, 
exhibits all the necessary data for growth comparison. Since 
these experiments were made it has been found that a frequent 
laboratory grade of acid potassium phosphate will give a Px 
anywhere from 3.5 to 4.5, but more frequently less than 4.0. 
Change in Py after plants had grown in the solution was fol- 
lowed in the case of peas, with a result much like that of the first 
series. The more acid solutions are shifted towards neutrality, 
but solutions with exponents greater than 5.8 or 6.0 may vary 
scarcely at all, while the more alkaline solutions are generally 
shifted toward neutrality. 
