268 
R. H. TRUE AND H. H. BARTLETT 
a constant interval of 12M X io~^ between members of the series. 
The experiment lasted 16 days. The results are plotted in figure 5. 
The same general characteristics noted in experiment 4 are again 
seen in this experiment and need not receive special mention. It will 
be noted in those concentrations exceeding the maximum salt content 
of experiment 4 that the toxic action of the salt became more marked, 
as was seen in the earlier onset of the antemortem leaching phase. 
The practical disappearance of an absorption phase in solutions about 
g6M X io~^ probably indicates the same thing. 
An interesting point to be noted in both experiments is the reduc- 
tion of the weaker solutions to a common salt content. In experiment 
4 on the tenth and eleventh days the weakest four Mg(N03)2 solutions 
and the distilled water check agreed in having an ion content of 
about 1271/ X 10-^ calculated as Mg(N03)2. Since the s^M X lO"^ 
solution was reduced to 12M X io~^ the net reduction in concentra- 
tion due to salt absorbed was approximately 2oikf X io~^. In some 
of the higher concentrations the reduction was somewhat greater. 
In experiment 5 a similar situation was seen. On the ninth and tenth 
days the weakest four salt solutions and distilled water had a like ion 
concentration, representing in the strongest of these four salt solutions 
a reduction of about 12M X io~^. This is somewhat greater than 
the average reduction in the solutions containing a considerable surplus 
of the salt. Again the best growth and the greatest absorption were 
found in a general way to coincide. 
Magnesium Sulphate. Experiment 6 
Magnesium sulphate solutions were made up in fourteen different 
concentrations, running from 12 to 16SM X io~^ the regular interval 
being 12M X io~^. The experiment ran thirteen days. 
The results graphically presented in figure 6 show that the action 
of magnesium sulphate is essentially the same as that of the nitrate. 
Those solutions having the least salt caused the excretion of electro- 
lytes from the roots. As the concentration increased to somewhat 
more than 24M X io~*' the roots were able to absorb, this absorption 
rising somewhat with the increase in concentration until a salt content 
equal to about I20ikf X io~^ was reached. Beyond this point, a 
further increase of salt was not accompanied by any increase of 
absorption. There was a tendency in the higher concentrations here 
used toward a reduction of absorption, due probably to the toxic 
