54 
RODNEY H. TRUE AND HARLEY HARRIS BARTLETT 
little more than half of the salt content of the solutions had been 
absorbed by the roots at the time of maximum absorption. In the 
most favorable mixtures the concentration of Ca++ was electrolytically 
more than equivalent to the sum of Mg++ + K+ and the two latter 
ions were either about equivalent, electrolytically, to one another, or 
else the K+ concentrations were somewhat more than equivalent 
electrolytically to the Mg++ concentration. In other words the 
numerical ratio of ions in the best mixtures was about 2 Ca++ : i Mg++ 
: 2K+. Further experiments, however, must be carried out before 
any great stress is laid on this ratio as the most favorable for 
absorption. 
Experiment 2. KH2PO4 + Ca(N03)2 + MGSO4 
This experiment was carried out in order to determine the extent 
to which the anions influence absorption. Accordingly, cultures were 
grown in solutions of potassium dihydrogen phosphate (which dis- 
sociates for the most part into the univalent ions K+ and H2P04~), 
calcium nitrate and magnesium sulphate. The composition and daily 
concentration of each solution is stated in Table 11,^ which is in every 
respect comparable with Table I. 
In figure 2 we have indicated the residual concentration of the 36 
culture solutions at the time of maximum absorption. Inspection 
of the table and the figure shows important differences between the 
cultures containing three anions and those containing only the NOs" 
anion. In but three out of 15 mixtures containing all three salts did 
the plants fail to show absorption during the first day. This result 
is in marked contrast to that of experiment i, and seems to indicate 
that root absorption was so active from the very start as to overbalance 
the effect of CO2 excretion. Rapid absorption was maintained in 
most of the mixtures throughout the experiment. 
The maximum absorption, attained after ten or eleven days, was 
in every case greater than in the corresponding nitrate solution, 
and was attained one or two days sooner. Whereas in the nitrate 
solutions only a third of the mixtures showed a total absorption 
^ Tahle II. — Concentration changes in culture solutions containing KH2PO4, 
Ca(N03)2 and MgS04, due to absorption and excretion of salts by roots of Lupinus 
albus. The initial concentration (140 N X io~^) of each solution is represented 
by 1.000. The daily concentration is therefore stated as a ratio of residual con- 
centration to initial concentration. To obtain the absolute concentration, in 
terms of N X io~^, multiply by 140. 
