322 RODNEY H. TRUE AND HARLEY HARRIS BARTLETT 
week. After this period a rapid loss of ions by the plant set in. 
A marked and well sustained net absorption was seen in the mixtures 
containing 2/4 and 1/4 Mg(N03)2, respectively, the maximum change 
in concentration being about 40 N X io~^ on the nth day in the 
solution containing equal parts of the two salts. 
It is clear that of this pair of kations Mg++ is more favorable to 
root absorption in the concentrations here used than K+. But for its 
relatively high degree of toxicity, which restricts life to a narrow range 
of concentrations, magnesium would bear a certain resemblance to 
calcium. Here as before potassium brings about a loss of ions by the 
plant. Nevertheless mixtures of the two nitrates are able to support 
a very considerable absorption, though it is little when compared v/ith 
mixtures containing Ca ions. 
The greatest absorption in the Mg-K series was made in the solu- 
tion containing 3/4 Mg(N03)2 + 1/4 KNO3 in a total concentration of 
240 N X 10-^ 
Mixtures of Mg and K ions showed in this experiment a marked 
superiority over either ion alone, as judged by the process of absorption. 
Summary of Results 
The chief results obtained in this series of experiments with the 
white lupine may be summarized as follows: 
1. When the nitrates of calcium, magnesium and potassium are 
offered in pairs in solutions varying in concentration from 120 N X io~^ 
to 480 N X io~^ it is usually the case that the roots absorb more 
electrolytes than from the pure solutions. It seems also true that for 
the range of concentration here concerned absorption tends to increase 
in mixtures as well as in pure solutions as the salt content increases. 
The case of magnesium salts offers an exception owing to the narrow 
range of physiologically useful concentrations of the Mg ion. 
2. In mixtures of Ca(N03)2 and KNO3 the inimical effect of K ions 
on root absorption is seen in the high ratio of Ca to K required to give 
maximum absorption, viz., 3 Ca++ : 2 K+ (3 Ca(N03)2 + 1/4 KNO3) 
in all concentrations tested. The value of a small amount of K ions 
is however proved by the excess of absorption in the mixture over 
that in Ca(N03)2 alone. The absolute amount of Ca present in 
mixtures seems to be of great influence since as the proportion of Ca 
increases in the greater dilutions, absorption is increased. The favor- 
able influence of Ca ions is therefore striking in the mixtures as well 
as in the pure solutions. 
