82 
Walter Stiles 
The influence of external concentration on the position of equilibrium. 
The observations already recorded suggest that the quantity of 
substance absorbed by the same tissue from a solution is relatively 
greater the diluter the solution, that is, the absorption ratio increases 
with dilution. The influence of the concentration of a solution ex¬ 
ternal to plant tissue on the position of the equilibrium attained in 
the intake of a number of salts has been investigated by Stiles and 
Kidd (1919 a) by means of the measurement of the electrical con¬ 
ductivity of the external solution. Experiments were carried out 
at constant temperature (20° C.) with carrot root and potato tuber 
in the form of circular disks i*8 cms. in diameter and 1 mm. in thick¬ 
ness, 40 such disks being immersed in 100 c.c. of solution. These 
experiments were all conducted in triplicate. For any series of 
experiments designed to yield comparable results all the disks used 
were cut at the same time and allowed to swell in water for a pre¬ 
liminary period. After mixing them well together each set of 40 disks 
was then taken from the general stock. The bottles used to contain 
the tissue and solutions were continuously shaken throughout the 
whole course of the experiment. This is a precaution to ensure regular 
results, as such treatment prevents the formation in the solutions 
of gentle diffusion gradients which may be unequal over different 
disks, especially when some of these lie on top of others. 
It has been pointed out by Stiles and Kidd that the decrease in 
the conductivity of the external solution may be assumed to be 
approximately proportional to the difference between absorption of 
the salt and exosmosis from the tissue. If the exosmosis into distilled 
water is determined and added to the values found in the experiments 
with salts, numbers proportional to the actual salt intake should 
be obtained provided there are no complications. That this is so 
cannot be assumed. 
Stiles and Kidd pointed out that the following actions would also 
bring about a decrease in conductivity and so make the values 
obtained for absorption in the way indicated, too high. 
(1) Reactions between the exudate and external solution by 
which non-ionised molecules are produced. This can be disregarded 
as a source of appreciable error having regard to the dilution of some 
of the solutions and the magnitude of the decreases with higher 
concentrations. 
(2) The exosmosis of non-electrolytes which by their mere presence 
would reduce the conductivity of the external solutions. The quantity 
of such substance which diffuses from the tissue is probably negligible. 
