512 BROOKLYN BOTANIC GARDEN MEMOIRS 
NO; ion is from four to five times as favorable for absorption under the 
conditions of these experiments as the Ca ion accompanied by the SO, 
anion. This seems to indicate a striking and specific difference in 
the influence of these anions on the absorptive activities of the squash. 
When the Ca ion is accompanied by the Cl ion, absorption is influenced 
very much as in the case of Ca acting with NO; ions. The favorable 
effect of NO; and Cl ions is contrasted with the action of the SO, ion. 
The strong influence exerted by the specific characteristics of the 
different species of plants is seen in the contrasting behavior of the 
lupine and the squash in the presence of Ca accompanied by the NO; 
ion. 
It should be borne in mind that the probable physiological inter- 
action of a given pair of ions is perhaps such as to make it unsafe to 
speak strictly of the specific action of any single ion irrespective of 
that of its companion ion or ions. 
It is obvious from what has been here shown that any theory of 
cell permeability which may be framed to account for the income 
and outgo of the living plant with respect to electrolytes must reckon 
with the striking differences that exist in the behavior of plants toward 
even such fundamental factors as the required mineral nutrient ions. 
