THE EXCHANGE OF IONS 
321 
a total concentration of 240 N X io~^ 
the best absorption took place in that 
containing 3/4 Mg(N03)2 + KNO3. 
Nearly as favorable was 1/4 Mg(N03)2 
+ 3/4 KNO3. These were both de- 
cidedly better than the pure Mg(N03)2 
solution. The greater loss of ions by 
roots in the mixture containing equal 
parts of the two salts is believed to 
be an aberrant result due perhaps to 
the use of less vigorous roots than 
those usually employed. Roots grow- 
ing in mixtures having a total concen- 
tration of 360 N X io~^ in every case 
absorbed more freely than from either 
of the unmixed solutions of the com- 
ponents. The 4/4 Mg(N03)2 solution 
was clearly toxic while in 4/4 KNO3 
the plants even at the height of the 
absorption phase were hardly able to 
recover a quantity of electrolytes 
equal to that previously lost. In all 
the mixtures a marked net absorption 
took place although it was somewhat 
less than in the case of the 240 N Xo~^ 
mixtures. The advantage seemed to 
lie with the solutions containing the 
lesser proportions of Mg(N03)2. 
In the group of solutions having a 
total salt content of 480 N X lO"^ the 
harmful action of 4/4 Mg(N03)2 and 
of themixturecontaining3/4Mg(N03)2 
was clearly marked on the 7th day. 
The higher concentration of the 4/4 
KNO3 solution seemed nevertheless to 
be more favorable to absorption than 
any of the lower concentrations, for 
a slight but undoubted net absorption 
of ions took place during the first 
\ 
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t 
/ 
-pf 
V 
4- 
I 
■/■ 
KF 
Y 
~D 
-M 
IS! 
ILL 
ED 
WA 
TEI 
f 
(NO 
'At 
SNO 
3 
Mg 
(NO 
3 
(fiM 
3 
NO 
? . 
a 3 ^ s e 
II 12 13 /♦ 
Fig. 3. Curves showing the change 
in concentration of the Mg(N03)2 
and KNO3 solutions used in experi- 
ment 3. 
