Hoagland 



— 130 — 



Plant Nutrition 



position so as to bring about increasing calcium ab- 

 sorption, increasing concentrations of oxalic acid ap- 

 peared in the plants. In certain instances a roughly 

 stoichiometric relation was observed. 



Textfigure 35. — Buffer contents of 

 composite expressed saps as influenced by 

 the nature of the salt supplied in the cul- 

 ture solution during solute absorption. In 

 this particular experiment the equivalents 

 of K and Br absorbed were approximately 

 the same. Br was absorbed to a much 

 greater extent than Ca. In this and the 

 following figure the acid titration values 

 reflect the organic acid contents of the 

 sap, in agreement with direct analysis. 

 (From Hoagland and Broyer, 1940). 



Emphasis is needed for the role of potassium in 

 sap buffer systems. Generally potassium is the chief 

 inorganic base in equilibrium with organic acid sys- 

 tems. The supposition has sometimes been made that 

 the absorption of calcium prevents the plant tissue 



