320 RODNEY H. TRUE AND HARLEY HARRIS BARTLETT 
favorable for absorption contained 2/4 or 1/4 Ca(N03)2- Although 
much less favorable for absorption than the solutions containing 
higher proportions of calcium nitrate, the solution containing but 
i/io Ca(N03)2 to 9/10 Mg(N03)2 was incomparably better than that 
containing 10/10 Mg(N03)2. In its effect upon absorption, as upon 
root growth, a small amount of calcium has an effect all out of propor- 
tion to the quantity actually present. 
Magnesium Nitrate and Potassium Nitrate. Experiment 3 
In this experiment, as before, four groups of solutions were made 
up having a total salt content of 120, 240, 360, and 480 N X io~^, 
respectively, each group containing solutions of the salts in the follow- 
ing proportions: 4/4 Mg(N03)2, 3/4 Mg(N03)2 + 1/4 KNO3, 2/4 
Mg(N03)2 + 2/4 KNO3, 1/4 Mg(N03)2 + 3/4 KNO3 and 4/4 KNO3. 
As in experiment i the anion concentration was the same for the 
five solutions of each group. Since in the mixtures an ion with a 
valence of two had to be replaced by two ions with a valence of i , the 
ratios of kations to anions formed the series 4 :8, 5 :8, 6 :8, 7 :8, 
and 8:8. The electrolytic conductivity of each solution was observed 
daily during an experimental period of 14 days. 
In the series of curves shown in figure 3 a number of novel features 
appear. The very general tendency of the root absorption to increase 
with the increase of the total salt concentration, so clearly seen in the 
foregoing experiments, is here absent. The best absorption in 4/4 
Mg(N03)2 took place in the weak 120 N X io~^ solution, although the 
240 N X io~^ solution was nearly as good. In the higher concentra- 
tions injury appeared only a few days after the experiment was begun 
as was indicated by a rapid loss of ions by the plants. 
The best absorption in 4/4 KNO3 was seen in the strongest solution 
where a distinct though brief net absorption phase lasted from the 
6th to 8th days. A minimal net absorption was seen in the 320 
N X io~^ solution on the 7th day. In the weaker solutions there was 
no net absorption. The greatest loss of salts by the plants occurred 
in the weakest solution. 
The roots made a net absorption in every mixture of whatever 
proportion or concentration. Among the mixtures with a total salt 
concentration of 120 N X io~^ none showed as great absorption as 
the 4/4 Mg(N03)2 solution. The roots showed a decreased absorption 
as the proportion of Mg(N03)2 was reduced. In the mixtures having 
