THE EXCHANGE OF IONS 
process. The greatest net absorption was seen after the 13th day in 
the mixture containing 3/4 Ca(N03)2 + 1/4 KNO3, from which the total 
amount of ions absorbed was approximately double that taken out of 
4/4 Ca(N03)2 solution. Absorption from the solution containing equal 
proportions of the two salts lagged slightly behind that from the full 
calcium solution during the first ten days but during the succeeding 
six days exceeded it. A somewhat similar record was made in the 
solution containing 1/4 Ca(N03)2 + 3/4 KNO3. The plants in this 
mixture absorbed for the first ten days practically as they did in the 
full Ca(N03)2 solution but showed a marked gain in the latter part of 
the period. Although the roots could not maintain a balance in favor 
of absorption when grown in a solution of pure KNO3, nevertheless this 
salt greatly facilitated absorption when it was mixed with Ca(N03)2. 
It also appears clear that a small proportion of Ca(N03)2 is able to 
give to a mixture containing a large proportion of KNO3 such properties 
as enable the roots to maintain active absorption. In the 240 N X 
10-6 group of solutions the mutually helpful influence of Ca and K 
ions in respect to absorption comes sharply to the front. 
In the third group of solutions each member had a total salt con- 
centration of 360 N X io~^. The effects on root absorption were in 
general like those seen in the last group. The increase of total salt 
content, however, seemed to cause an increased absorption of ions 
from all solutions. Although in the KNO3 solution a net gain in ions 
by the plant was not indicated at any time, there was an absorption 
phase between the third and eighth days, succeeded by the usual 
period of loss during the remainder of the experiment. In the 
4/4 Ca(N03)2 solution root absorption was greater than in the less 
concentrated solutions of this salt. The maximum reduction in the 
concentration of the solution, attained during the period from the 
ninth to the twelfth day, was over 72 N X io~^. The greatly increased 
absorption in the mixture containing 3/4 Ca(N03)2 to 1/4 KNO3 was 
very striking, the maximum quantity of electrolytes gained by the 
plants prior to the fourteenth day being indicated by a change of 
about 158 N X io~^ in the concentration of the culture solution, i. e., 
over double that gained from the pure solution of Ca(N03)2. In the 
solution containing 2/4 Ca(N03)2 + 2/4 KNO3 the maximum absorp- 
tion was reached about the fourteenth day and caused a reduction of 
about 102 N X io~^ in the concentration of the culture solution, a 
markedly greater absorption than that from the 4/4 Ca(N03)2 solution. 
