1920] 
DUGGAR—H-ION CONCENTRATION AND NUTRIENT SOLUTIONS 41 
In general, when the reactions of the culture solutions (such 
as have been employed in this work) are strongly acid, the con- 
tact with plant roots effects a change towards neutrality. The 
extent and rapidity of this change, however, depend somewhat 
upon the crop, and especially upon the composition of the cul- 
ture solution. It may be noted, for instance, from tables xr- 
XIX that solution A never became neutral, while solution C was 
changed, in the extreme case, to Px 8.6. On the other hand, it is 
not necessarily true that alkaline culture solutions tend to be- 
come acid, as may be seen in the case of solution C. Solution 
B, normally near the neutral point, may be shifted slightly in 
either direction. 
Impelled in part by the general experience of others in field 
work, indicating a general tendency of cultivated soils to become 
acid, Breazeale and Le Clerc (12) undertook solution-culture 
experiments to determine “the effect of the reaction of the 
culture medium on the growth of wheat seedlings and particu- 
larly on the development of the root," with a view to a possible 
explanation of the results obtained in practical agriculture. 
They regard the acid tendency as due primarily to the decay of 
organie matter and secondarily to the selective action of the 
root; the last mentioned only they proposed to investigate. 
Their experiments were chiefly with certain salts, particularly 
KCl, K;50,, and NaNO,, used singly and each in combination 
with solid CaCO;. According to their results greater absorption 
of the K ion, when the potassium salts are used, caused the 
solution to become acid; while in the case of the sodium salt, the 
greater absorption of the NO; ion tended to produce alkalinity. 
The addition of caleium carbonate precludes the development of 
acid with the potassium salts. In the toxic action reported no 
account is taken of the lack of physiological balance in the 
solutions lacking Ca, and no experiments were made with KNO.. 
Moreover, only a titration method (consistent with the general 
usage at that time) was employed in determining acidity and 
alkalinity. 
Some time previous to this Hartwell and Pember (07) 
emphasized the ““marked property of the seedlings [wheat, rye, 
barley, and oats] of rendering the nutrient solutions alkaline—," 
insufficient, however, to cause precipitation. Similar observa- 
tions are numerous in the literature. 
