3i8 
RODNEY H. TRUE AND HARLEY HARRIS BARTLETT 
In this series of cultures it was again noted that in general absorp- 
tion increased with the increasing total salt concentration, although not 
proportionately. The Mg(N03)2 solutions were an exception to this 
otherwise general rule, owing to the great toxicity of this salt. 
In the 120 N X io~"^ group of solutions the solutions gained ions 
for a period of two or three days. It is probable that in both the Mg 
and the Ca solutions there was some excretion of salts from the plants, 
since nearly a week passed before this loss was made up, whereas the 
smaller apparent loss seen in the case of the mixtures might all be 
accounted for by the increase in the CO2 content of the solutions. It 
will be noted that in the solution of Ca(N03)2 after the initial period of 
about two days marked by an active loss of ions, absorption began to 
take place with increasing rapidity until near the end of the experi- 
ment a net decrease of nearly 90 N X io~^ had taken place in the 
concentration of the solution. The record for Mg(N03)2 was similar 
to that for Ca(N03)2 for seven days after, which time absorption 
slackened and the solution stood at equilibrium with a small net 
absorption until near the end of the experimental period, when loss of 
salts from the roots set in and lasted until the experiment closed. 
In all mixed solutions a more active absorption was made during the 
first 12 days than in either of the unmixed solutions. It will be noted 
that the greatest net absorption took place from the solution contain- 
ing 1/4 Ca(N03)2 + 3/4 Mg(N03)2 although late in the experiment the 
plants in that containing 2/4 Ca(N03)2 + 2/4 Mg(N03)2 reached 
practically the same maximum, exceeding that made in the 4/4 
Ca(N03)2 by a very small margin. The solution containing i/io 
Ca(N03)2 + 9/10 Mg(N03)2 showed a loss in concentration of over 
60 N X 10-6 against about 12 N X IQ-^ for 10/10 Mg(N03)2. The 
net absorption from the 4/4 Mg(N03)2 solution was multiplied five 
times by the replacement of one-tenth of the magnesium by calcium. 
In the 240 N X io~^ group the characteristic features are: (i) the 
increased and nearly parallel absorption for thirteen days from the 
solutions containing 4/4 Ca(N03)2, 2/4 Ca(N03)2 + 2/4 Mg(N03)2, and 
1/4 Ca(N03)2 + 3/4 Mg(N03)2; (2) the lengthening of the period of 
active absorption with the increase of the quantity of Ca(N03)2 
present; (3) the failure of absorption in the solution containing 
i/io Ca(N03)2 + 9/10 Mg(N03)2 to keep its place relative to the 
other mixtures; and the long delayed and brief period of sHght net 
absorption from the solution containing 4/4 Mg(N03)2. 
