264 
R. H. TRUE AND H. H. BARTLETT 
able to make some absorption, leaving even the weakest solution 
poorer in ions than it was at the beginning of the experiment. In 
general, net absorption increased with the increase of the original salt 
content up to a concentration of 40M X lO"*'. In this and in the 
more concentrated solutions the maximum absorption varied some- 
what but did not advance with the increasing salt content. This 
seems to mean that the demand for this salt under the conditions to 
which the plants were subjected was satisfied by a concentration of 
48M X 10-6. 
The growth rate in general increases with the concentration in the 
more dilute members of the series and reaches a general level which 
with considerable variation is maintained. This general level is attained 
at the point of maximum absorption. 
Calcium Sulphate. Experiment 3 
Fourteen solutions of calcium sulphate were studied, in concentra- 
tion ranging from 12 to 16SM X io~^, the regular interval between 
adjacent members of the series being 12M X I0"~^. The experiment 
ran seventeen days, during which time great temperature variations 
were noted. 
The curves presented in figure 3 show a very active absorption 
by the roots in all the solutions, excepting only the distilled water 
check. As usual, the distilled water extracted electrolytes from the 
roots until a fairly constant concentration was reached at which 
excretion was perhaps balanced by the reabsorption of the same ions. 
The phase of balance between the two processes was followed by the 
usual increavsing leakage of electrolytes from the roots as they ap- 
proached exhaustion. 
In all CaS04 solutions from 12 to 72 M X io~^ absorption was 
active, beginning in the upper part of this range on the first day of 
the experiment. Under the influence of this absorption the ion con- 
centration of the six weaker solutions fell rapidly to a point approaching 
on about the tenth day that of the distilled water at that time and 
becoming much weaker in ions toward the close of the experiment than 
even the distilled water itself. It is probable that in these more 
dilute solutions the roots absorbed practically all the salts they could 
and reduced the concentration to the unavailable minimum. This 
unavailable minimum was represented by a concentration of CaS04 
from 12 to iSM X io~^. A culture containing 500 c.c. of a yiM 
