50 RODNEY H. TRUE AND HARLEY HARRIS BARTLETT 
salts, and the interior positions the mixtures of all three salts. The 
method used in carrying out the present work was exactly that detailed 
in previous papers. The electrical conductivity of each solution was 
read before the lupine seedlings were placed in it. During the progress 
of the experiments the conductivity and temperature of the solutions 
were read daily. Unfortunately temperature regulation was im- 
possible, but the conductivities were of course reduced to a uniform 
temperature. The effect of temperature on absorption is still to be 
determined. From some of the experiments reported in our former 
papers it appears that the temperature effect within a limited range is 
not great. Since further work must be done in order to determine 
the precise effect of temperature on absorption, we have not included 
the daily temperature readings in this paper. 
Experiment i. KNO3 + Ca(N03)2 + Mg(N03)2 
This experiment was carried out with the nitrates of potassium, 
calcium and magnesium, and lasted 16 days. The composition and 
daily concentration of each solution is expressed in Table I.^ To 
facilitate interpretation the original concentration of each solution 
is taken as unity. In this way the magnitude of absorption or excre- 
tion as compared with the total original concentration is most readily 
made apparent. It was impossible, on account of the large number of 
culture solutions, to state the results intelligibly by means of curves. 
A concentration greater than unity indicates that excretion of elec- 
trolytes from the roots has taken place; absorption, on the contrary, 
is indicated if the concentration is less than unity. 
In figure i we have stated on a triangular diagram the residual 
concentrations of the 36 culture solutions at the time of maximum 
absorption. The residual concentration is stated, as in the table, as 
a fraction of the original concentration. The greatest absorption 
was of course attained in different solutions on different days. Each 
point in the figure represents a solution, the original composition of 
which is indicated on the three intersecting axes reading upwardly 
from the intersection. The sum of the numerals on the three axes 
^ Table I. — Concentration changes in culture solutions containing KNO3, 
Ca(N03)2 and Mg(N03)2, due to absorption and excretion of electrolytes by roots of 
Lupinus alhus. The initial concentration (140 N X io~^) of each solution is repre- 
sented by 1.000. The daily concentration is therefore stated as a ratio of residual 
concentration to initial concentration. To obtain the absolute concentration, in 
terms of N X io~^ multiply by 140. 
