466 
Journal of Agricultural Research 
Vol. XXV, No. 11 
Every strain of corn from these different plantings showed variations 
in the acidity measurements parallel to those of the group averages of 
Table VI. To illustrate graphically a typical instance, the electrometric 
titration curves obtained with plants of a representative strain, No. 315, 
from the four greenhouse plantings, are plotted side by side in figure 2. 
Whatever may be the cause of the differences in the vegetative vigor 
of these series and the correspondingly wide variation in their cell-sap 
acidity, temperature may be excluded except for Series V, by reason of 
the unrelated sequence of good and poor series. The illumination was 
probably nearly the same for all the series, especially for those grown 
within the same greenhouse. Since com has been found (j, 3,4, 9, jo, 14, 
15,17) to grow well in soils and nutrient solutions of even higher acidity 
than that of the poorest plot (P H 6.2), soil acidity can probably be elimi¬ 
nated as a causal factor. From the facts that the vigorous Series I and 
IV were grown in deeper soil than were Series II and III, and, that the 
Fig. a.—Electrometric titration curves of the juice of tops of Reid Yellow Dent com from the four 
greenhouse plantings, illustrating the correlation of activity measurements with vegetative vigor. 
poorest series, III, was planted in relatively shallow soil which had 
already been partly exhausted by one crop (Series II) it would appear 
that the inadequacy of some soil constituents was responsible for the 
spindling growth and high acidity of Series II and especially of III. 
Series V evidently was stunted as a result of low temperatures, since it 
is common experience that the cool nights of early fall prevent good 
growth of corn. 
Consistent with the inverse relation between vegetative vigor and acid 
accumulation brought out by intercomparisons of the series or of the 
strains composing them, are those individual measurements (Tables I, II, 
III, IV) which show a lower acidity of the more vigorous individuals of 
the same strain as compared to the poorer ones growing beside them. 
This was true not only of the leaf juice but also of that of the stalk, the 
latter showing the correlation the more strikingly. Occasional depar¬ 
tures from the rule occurred and from these exceptions it is evident that 
neither green weight nor height are invariably indications of relative 
acidity. A short stalky plant was occasionally less acid than a tall more 
slender one which had been judged the better plant. 
