ROOT ABSORPTION 
Another class of factors depends upon the plant for their values. 
Such would be the chemical character of the cell wall and the deeper 
lying cell membranes and other structures. These membranes con- 
tain dissociating substances, such as calcium pectate and many other 
substances (3) . The value of the minimum concentration for absorption 
must be determined by the balance of ion interchange between the 
membrane surface and the solution. It would seem likely that when 
the syntheses within the cell which tend actively to withdraw ions 
toward the interior is balanced by the tendency toward dissociation 
and loss of ions at the bounding membrane, the condition here seen 
would be realized. 
Since both of the internal factors here mentioned depend on struc- 
ture and function supposed to be specific, it is hardly surprising that 
this minimum concentration should also be specific. To test this 
point corn was grown in conductivity water for 10 days after equili- 
brium had been established. For six cultures of five plants each the 
variation during this period was io-i8w x io~*^ expressed as KCl. At 
the end of that time the solution in one beaker was boiled to remove 
CO2, made up to its original weight with recently distilled conductivity 
water, stoppered to prevent the absorption of CO2, and read at 18° C. 
The total concentration before boiling was 11 x io~^n as KCl. The 
CO2 concentration was 6 x io~^n as KCl, leaving a residual concen- 
tration of 5 X io~^n of non-volatile electrolytes which the corn is unable 
to absorb. Squashes were then placed in the set-up. That the solu- 
tion was not in equilibrium with the squash was shown by the rise in 
concentration, much as is seen in distilled water. After a period of 
leach and subsequent absorption, equilibrium was estabhshed at a 
concentration higher than the value for corn. Infection occurred in 
one culture, a fact which became apparent in the continual leach of 
electrolytes. The beaker having the lowest value was tested as 
before. The concentration before boiling was 28.7, after boiling 22. 3^ 
X io~^ KCl, leaving a residual concentration of 6.4/7 x io~^ expressed 
as KCl, which is due to volatile electrolytes. The close agreement 
with the former value for CO2 is apparent as well as the higher average 
value for the equihbrium concentration maintained by the squash. The 
squash was again replaced by corn and the concentration sank to its 
former value for corn in all cultures except the one which became 
infected. 
In a recent article Stiles (4) says: "It is quite conceivable that 
