134 
Walter Stiles 
The Influence of the Presence of one Dissolved 
Substance on the Absorption of Another 
So far, our consideration of the intake of dissolved substances has 
been limited to substances presented to the plant in pure solution. 
We have now to consider how this intake is affected when more than 
one substance is present in solution in the external medium. It has 
already been mentioned in Chapter iv that the presence of a non¬ 
electrolyte like sugar or glycerol reduces the rate of diffusion of an 
electrolyte, while in Chapter v reference has been made to the 
retardation or inhibition of diffusion through porcelain membranes 
that can be brought about by blocking the pores of the membrane 
with some substance. It would not then be surprising to find that 
the presence of one substance in the external solution should hinder 
the intake of another. 
That the presence of a second substance dissolved in the external 
medium reduces the harmful action of a toxic substance in the 
solution external to living tissue has long been recognised (cf. 
Brenchley, 1914 b, Stiles and Jprgensen, 1914 b). Such a result does 
not, in itself, prove that the actual entrance of the toxic substance 
is prevented or retarded. The seat of the depoisoning action may be 
inside the plant. However, there is considerable evidence that this 
“antagonism” between dissolved substances is actually due to a 
mutual hindrance to their entrance into plant cells; this evidence 
it will be necessary for us to discuss. 
This antagonistic action was brought into prominence by the work 
of Loeb (1900, 1901, 1902, 1905, 1906; Loeb and Gies, 1902) on the 
development of the eggs of the marine fish Fundulus. Development 
of these eggs is inhibited if they are put immediately after fertilisa¬ 
tion into a pure solution of sodium chloride having the same con¬ 
centration as that of this salt in sea water. But if a small quantity 
of the salt of a bivalent metal such as calcium, strontium, magnesium, 
or even lead, is added to the sodium chloride solution, development 
of the egg into an embryo is able to proceed. The result depends on 
the kations, as different salts of the same metals are able to act equally 
well as depoisoners. The antagonism between monovalent and bi¬ 
valent kations is also shown in the depoisoning action of a monovalent 
kation towards the poisonous action of a bivalent metal such as zinc. 
Slight antagonism was also observed between two divalent kations, 
as, for example, strontium and magnesium. 
