512 BROOKLYN BOTANIC GARDEN MEMOIRS 



NO3 ion is from four to five times as favorable ior absorption under the 

 conditions of these experiments as the Ca ion accompanied by the SO4 

 anion. This seems to indicate a striking and specific diff^erence in 

 the influence of these anions on the absorptive activities of the squash. 

 When the Ca ion is accompanied by the CI ion, absorption is influenced 

 very much as in the case of Ca acting with NO3 ions. The favorable 

 effect of NO3 and CI ions is contrasted with the action of the SO4 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 NO3 

 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. 



