THE BALANCING FUNCTION OF SALTS 129 



such as age of plant, time of year, other elements present in the 

 soil, etc. Physiological balance is thus seen to be such a complex 

 matter that comparatively few results which can be applied by 

 the farmer have yet been obtained. 



QUESTIONS 



1. What is meant by permeability? 



2. In what part of the cell do changes in permeability occur? 



3. What is an electrostatic theory? 



4. Which is more important in balanced solutions — the concentration of 

 the salts or their ratio to one another? 



5. Are acid solutions rich in positive or negative charges? Why? 



6. What is the difference between total acidity and hydrogen ion concen- 

 tration? + 



7. When the pH value increases, does the H ion concentration decrease or 



increase? + 



8. At pH 7 how does the number of H ions in a solution compare with the 



number at pH 8? 



9. What is meant by the statement that the pH value varies inversely 



+ 

 with the H ion concentration? 



10. Which is more actively acid, a solution of pH 8 or one of pH 10? 



11. What is the meaning of the "p" in "pH"? Why not "nH"? 



REFERENCES 



Addoms, R.— The effect of the hydrogen ion concentration on the protoplasm 



of the root hairs of wheat. Am. J. Bot., 10:211, 1923. 

 Clowes, G. H. A.— On the action exerted by antagonistic electrolytes on the 



permeability of emulsion membranes. Proc. Soc. Exp. Biol, and Med., 



15:108, 1918. 

 Gericke, W— On the physiological balance in nutrient solutions for plant 



cultures. Am. J. Bot., 9:180, 1922. 

 Kurz, H. — Hydrogen ion concentration in relation to ecological factors. 



Bot. Gaz., 76:1, 1923. 

 Loeb, J.— The origin of the conception of physiologically balanced solutions. 



/. Biol. Chem., 34:503, 1918. 

 Raber, O. — Permeability of the cell to electrolytes. Bot. Gaz., 75:298, 1923. 



The permeability of the cell. Bot. Gaz., 81:348, 1926. 



Reed, H. S— The absorption of sodium and calcium by wheat seedlings. 



Bot. Gaz., 66:374, 1918. 

 Stiles, W.— Permeability. Sci. Prog., 20:417, 1926. 



Permeability and related questions. Sci. Prog., 23:50, 1928. 



Waynick, D. D— Chemical composition of the plant as further proof of the 



close relation between antagonism and cell permeability. U. Calif. Ag. 



Sci. Pub., 3:135, 1918. 

 Wherry, E. T— The soil reaction preferences of certain plant orders. Jour. 



Wash. Acad. Sci., 17:148, 1927. 



