The plants of this experiment developed very rapidly, 
RECORD OF THE EXPERIMENTS. 35 
and had 
reached a state of maximum root development after six days. At 
this time the equilibri- 
um concentration was 
5M be} 
500,c00, -"'s 
less than that found for 
solutions of magne- 
sium or calcium alone, 
or for magnesium and 
calcium in the molec- 
about 
ular ratio 2 The 
absorption efficiency 
was so great that all 
solutions which at the 
start were above equi- 
librium concentration 
were brought below it 
before the rate of ex- 
cretion became greater 
than the rate of ab- 
sorption. This was 
not the case in any 
other experiment. In 
figure 21 there are 
three curves. Theone 
which represents the 
solutions at the end 
of six days gives the 
true equilibrium con- 
centration, for up to 
that time the roots 
had been actively 
growing. The other 
‘NG CGHOW7H. 
aS IN CONCENTRATION DUA 
A7| | 
eS 
‘ee 
So (aE e 
500, 000 
Fic. 21.—Curves showing relation of initial concentration of the cul- 
ture solutions to subsequent excretion and absorption ofsalts by pea 
roots in solutions of Mg(NOz)2+Ca(N0O3)2 in the molecular ratio }. 
curves merely indicate the rate at which the salt content of roots 
which are no longer actively growing passes into the culture solutions. 
CONCLUSIONS. 
Our work on the relation of roots to dilute solutions of calcium and 
magnesium nitrates has thus far shown: (1) That there is a definite 
1 It is obvious that in every culture whose development is limited by lack of light, the entire salt content 
of the root system must ultimately, as vitality wanes, pass into the culture solution. With peas, the rate 
of outgo exceeds the rate of intake as soon as root growth stops, long before the roots die or the cotyledons 
are exhausted. 
231 
