200 hvdi{0(;ex iox coxcextuatiox ix s.a. soils. 



pH6*3. The one next to this gave pH5'8. All the others right to 

 the youngest leaf gave pHo'o — 5'6. The acidity of the cell sap 

 appears therefore to remain remarkably constant throughout the 

 hfe of the leaves, but shows a decrease as the end of the life 

 period is reached. Probably this decrease is due to the with- 

 drawal of organic acids from the dying leaf. 



The determination of the hydrogen ion concentration of plant 

 juices has been carried out by Truog and Meacham/" Clevenger/^ 

 and Haas,^" whose papers (reviewed by E. J. Salisbury in Journ. 

 Ecol., VIII, 3, 1920) are cited in the accompanying bibliography. 



References. 



The Theory of Hydrogen Ion Concentration and of Determining pH. 



1. Prideaux, E. B. R. " The Theory and Use of Indicators." London, 



1917. 



2. Evers, N.. and Gamble, F. W. " Modern Ideas respecting Acidity and 



Alkalinity." P/iannarPifficaf Jouniul Reprint, 1922. 



Soil Reaction and Its Application to Plant Ecology. 



3. Fisher, E. A. " Soil Reaction." Science Progress, 63, Jan. 1922, 



p. 408. 



4. Arrhenius, 0. " Ocologische Studien in den Stockholmer Scharen." 



7]r}/rkeriaktiebrlaget. Sve.a, Stockholm, Sweden, 1920. 

 (Reviewed by Wherry in Ecolncin, II, 3, 1921.) 



5. Wherry, E. T. " Plant Distribntion around Salt Marshes in Relation 



to Soil Acidity." Ecology, I. 1, 1920. 



6. Wherry. E. T. " Soil Aciditv and a Field Method for its Measure- 



ment." Ecology, I, 3, 1920.' 



7. Salisbury, E. J. "Stratification and Hydrogen Ion Concentration of 



the Soil in Relation to Leaching and Plant Succession with special 

 reference to Woodlands." Jotirnal of Ecology, IX, 2, 1922. 



8. Fred, E. B., and Davenport, A. " Influence of Reaction on Nitrogen 



Assimilating Bacteria." Journ. Agrlc. lUsmrch, 14. 

 (Reviewed by M. C. Rayner in jinirn. Ecol., VIII, 3, 1920.) 



9. Gainey, P. L. " Soil Reaction and the Growth of Azotobacter." Journ. 



Af/ric. Research, 14. (Reviewed bv M. C. Ravner in Journ. Ecol.. 

 Vill, 3, 1920.) 



Application to Plant Juices. 



10. Truog. E., and Meacham, M. R. " Soil Acidity. Its Relation to the 



Acidity of the Plant Juice." Soil Science, 7. 1919. 



11. Clevenger, C. C. " Hydrogen Ion Concentration of Plant Juices." 



Soil Science, 8, 1919. 



12. Haas, A. R. C. " Reaction of Plant Juices." Soil Science. 9. 1920. 



Papers on South African Soils. 



13. Juritz, C. F. " A Study of Agricultural Soils of the Cape Colony." 



Capetown. 1910. 



14. Juritz, C. F. " Recent Soil Investigations in the Cape Province." 



Agr. Journ., Union of S. Africa, V, 6, 1914. 



15. Juritz, C. F. " The Wheat Soils of Alexandria Division, Cape Pro- 



vince." S. Afr. Journal of Science, XIII, 6, 1917. 



16. Marchand, B. de C. " Fertilisers." Bull. Xo. 19. Union S. Afr., 



Dept. of Mines and Industries, 1919. 



17. Hall, T. D. " The Lime Requirements of some South African Soils." 



Journ. S. Afr. A.o.'^oc. Anal. C/iem., IV, 2, 1921. 



18. Hall, T. D. " Nitrification in some S. African Soils." Soil Science, 



XII. 4, 1921. 



19. Hall, T. D. " The Lime Requirement of Soil and Plant." Union of 



S. Africa Journ. Dcpf. of Agric Reprint No. 3, 1922. 



20. Watt, R. D. " Nitrification in Transvaal Soils." Transvaal Dept. of 



Agric. Annual Report, 1908. 



