THE EXCHANGE OF IONS 
267 
centration of 80M X 10"^ After showing the usual record of absorp- 
tion for eight days, the solution on the ninth day showed a marked 
increase in ions. This increase was 
continued at a rapid and rather uni- 
form rate till the close of the experi- 
ment. An examination at that time 
showed that one plant was injured at 
a point near the surface of the solu- 
tion and by the leaching of electro- 
lytes from the dead tissues had fur- 
nished a source of contamination. 
A study of the growth of the pri- 
mary roots in the different solutions 
of Mg(N03)2 showed that while in the 
lower and higher concentrations the 
rate was about equal to that seen in 
distilled water, a better growth pre- 
vailed in the medium concentrations 
(32 to 72ikfXio-^) with a fairly well 
marked maximum in solutions 48 to 
64M X 10-^ This region of better 
growth coincided fairly well with that 
in which the maximum absorption 
took place. There were many evi- 
dences of toxic action in the stronger 
concentrations. The great reduction 
of the laterals, the development on 
the primary roots of occasional dis- 
colored tissue and the frequent ap- 
pearance of reddish blotches at the 
bases of the hypocotyls may be men- 
tioned here. These characteristics of 
Mg action will be again referred to in 
connection with another experiment 
involving higher concentrations in 
which these features come out more 
clearly. 
In experiment 5, a second series of thirteen solutions of Mg(N03)2 
was used in concentrations lying between 12 and X I0~^ with 
J 
\ 
\ 
\ 
\ 
\ 
t 
^/ 
\ 
\ 
N 
\ 
\ 
\ 
/ 
Fig. 4. Curves showing the changes 
in concentration of Mg(N03)2 solu- 
tions used in experiment 4. 
