266 
R. H. TRUE AND H. H. BARTLETT 
salt concentration the maximum net absorption did not rise, seeming 
to indicate a surplus of calcium sulphate over the quantity which 
could be absorbed. 
The root growth in the more dilute solutions seemed to increase 
with the increase in CaS04 concentration but in the more concentrated 
solutions no increasing root growth was apparent. In general there 
was a rough parallelism between root growth and absorption of CaS04. 
Neither increased indefinitely as the initial concentration of the 
culture solution was increased. 
Magnesium Nitrate. Experiments 4 and 5 
In experiment 4 thirteen solutions of Mg(N03)2 were used ranging 
in concentration between 8 and 104M X io~^ with a constant differ- 
ence of SM X io~^ between members of the series. In view of the 
markedly toxic properties of magnesium salts the concentrations used 
were less than in the case of the calcium salts. The course of the 
experiment covered fourteen days. Here, as in the Ca(N03)2 solu- 
tions, the roots were unable to absorb electrolytes during the first 
day in a quantity sufficient to make up for the real and apparent 
losses. In the weaker solutions (8 to 24ikf X lO"^) the loss prepon- 
derated over such possible absorption as may have taken place so 
greatly for the first four days as to leave the solutions markedly 
richer in ions than at the beginning of the experiment. It will be 
noted that the net loss of ions from roots was greater in the most 
dilute vsolutions (8 and 16M X io~*^). In the more concentrated 
members of the series, absorption predominated more promptly over 
loss and at a generally increasing ratio as the concentration increased. 
This was seen both in the shortening of the preliminary period of 
apparent loss and in the greater rapidity of absorption during com- 
parable intervals. In general, absorption began to assume its most 
rapid rate after the elapse of about four days and continued to show 
this maximum rate for the succeeding seven or eight days. At about 
the twelfth day, or, in the more dilute members of the series a day 
earlier, the roots began to lose ions more rapidly than they absorbed 
them, a reversal of action due probably to approaching exhaustion. 
This loss rapidly increased and the more dilute solutions at the close 
of the experimental period were richer in electrolytes than at the 
beginning. 
An instructive accident happened in the culture containing a con- 
