210 
Journal of Agricultural Research 
Vol. XXVII, No. 
EXPERIMENTAL WORK 
PROCEDURE 
An indirect method was used in this investigation. Only two explana¬ 
tions of the changes which take place in media under the influence of 
growing seedlings seem possible—neutralization by root excreta and 
selective absorption. 
In the case of neutralization, the effect produced by the growing seed¬ 
lings should be independent of the kind of acid used, as long as the initial 
hydrogen-ion concentration and the dissociation constants are the same. 
In the case of selective absorption, however, the effect of the seedlings 
in decreasing acidity should depend upon the chemical composition of the 
acid used. For instance, it would seem that, other factors being equal, 
the rate and absolute quantity of diminution in acidity will be greater in 
solutions of nitric acid than in solutions of hydrochloric acid, since nitro¬ 
gen is a more essential element of plant food than chlorin. Accordingly, 
seedlings were grown in solutions of several acids of definite initial 
hydrogen-ion concentrations, and the changes in active acidity of these 
solutions were compared at intervals. It is assumed that the principles 
which govern hydrogen-ion concentration phenomena are essentially the 
same in solutions of pure acids and alkalies as in more complex nutrient 
solutions with an acid or alkaline reaction. 
Only distilled water solutions were employed, as the use of nutrient 
solutions with the acids would have led to complications likely to in¬ 
terfere with a clear interpretation of the results. For instance, Conner 
and Sears (4) added hydrochloric, nitric, sulphuric, and phosphoric acids, 
respectively, to a Tottingham solution. As this solution contains phos¬ 
phates, the addition of a strong acid would naturally cause liberation of 
phosphoric acid to an extent corresponding to equilibrium relations. 
Consequently these authors investigated largely phosphoric acid. 
Another source of complication resulting from the use of a nutrient 
solution in this connection would be the change in its composition caused 
by the feeding activities of the seedlings, with the resulting establishment 
of new equilibria between the elements. Using the present method, 
practically only two factors need to be reckoned with—the seedlings and 
the kind of acids. 
PREPARATION OF WATER CULTURES 
Wheat seeds were germinated on large perforated aluminum disks 
floating in tap water, and the seedlings were grown there until they were 
about 2 inches high. Glasses of approximately 225 cc. capacity con¬ 
taining tap water were covered with paraffined paper perforated with 
holes smaller than the size of average wheat seeds. The rootlets of the 
seedlings were then introduced through these holes into the glasses, so 
that the seeds and plumules rested on the paraffined paper without com¬ 
ing in contact with the liquid media. The seedlings were grown in tap 
water for about two days to allow good root development and then for a 
day in distilled water before they were finally transferred to the experi¬ 
mental solutions. 
When plants grow in the soil, the seeds are in contact with the same 
medium as the seedlings, and they may participate in the changes in 
reaction produced in the medium. In fact, Rudolfs (9) found that 
