COLLOID CHEMISTRY OF THE SOIL IN RELATION TO PLANT NUTRITION 735 



acterization of the exchange complex. At what ratios do deficiency 

 symptoms appear, and what variabihty is there under the conditions of 

 agricultural practice? The answers to these questions are already being 

 sought in many laboratories. 



References 



Arnon D. I., and Grossenbacher, K. A., 1947. "Nutrient Culture of Crops with 



the Use of Synthetic Ion Exchange Material," Soil Sci. 63, 159. 

 Barber, S. A., and Marshall, C. E., 1951. "Ionization of Soils and Soil Colloids, 



II: Potassium-Calcium Relationships in MontmoriUonite Group Clays in 



Attapulgite," Soil Sci. 72, 373. 

 Barber, S. A., and Marshall, C. E., 1952. "Ionization of Soils and Soil Colloids, 



III: Potassium-Calcium Relationships in Illite, Kaolinite and Halloysite," 



Soil Sci. 73, 403. 

 Bartlett R. J., and McLean E. O., 1959. "Effect of Potassium and Calcium 



Activities in Clay Suspensions and Solutions on Plant Uptake;" Soil Sci. Soc. 



Am. Proc. 23, 285. 

 Bloksma, A. H., 1957. "The Diffusion of Sodium and Iodide Ions and of Urea in 



Clay Pastes," /. Coll. Sci. 14, 40. 

 Brydon, J. E., and Marshall C. E., 195&: Mineralogy and Chemistry of the 



Hagerstown Soil in Missouri, Missouri Agricultural Experimental Station, 



Research Bulletin 655. 

 Coleman, N. T., et al., 1951. "On the Validity of Interpretations of Potentiometri- 



cally measured Soil pH," Soil Soc. Sci. Am. Proc. 15, 106. 

 Danielson, R. E., and Russell, M. B., 1957. "Ion Absorption by Com Roots as 



Influenced by Moisture and Aeration," Soil Sci. Soc. Am. Proc. 21, 3. 

 Deshpande, K. B., and Marshall C. E., 1959. "An Interpretation of Electro- 

 chemical Measurements on a MontmoriUonite Clay," /. Phys. Chem. 63, 1659. 

 Epstein, E., and Hagan, C. E., 1952. "Kinetic Study of the Absorption of Alkali 



Cations by Barley Roots," Plant Physiol. 27, 457. 

 Higdon, W. T., 1957. "An Experimental Study of Three Chemical Theories of 



Cation Uptake by Plants," Doctoral thesis, University of Missouri. 

 Higdon, W. T., and Marshall, C. E., 1959. "The Uptake of Ca and K by Young 



Soybean Plants," Missouri Agricultural Experimental Station Research Bul- 

 letin 716. 

 Kemper, W. D., 1960. "Water and Ion Movement in Thin Film as Influenced by 



the Electrostatic Charge and Diffuse Layer of Cations Associated with Clay 



Mineral Surfaces," Soil Sci. Soc. Am. Proc. 24, 10. 

 Klute, A., and Letey, J., 1959. "The Dependence of Ionic Diffusion on the 



Moisture Content of Nonadsorbing Porus Media," Soil Sci. Soc. Am. Proc. 23, 



213. 

 Lundegardh, H., 1943. "Electrochemical Relations Between Root Systems and 



Soil," Soil Sci. 54, 177. 

 McLean, E. O., 1948. "The Measurement of Potassium and Calcium Activities by 



Means of Clay Membrane Electrodes in Homionic and Polyionic Systems 



including Plant Cultures," Doctoral thesis, University of Missouri. 

 Marshall, C. E., 1951. "The Activities of Cations Held by Soil Colloids and the 



Chemical Environment of Plant Roots," in Truog, E., ed.. Mineral Nutrition 



of Plants ( Madison, Wise, U. of Wisconsin in press). 

 Marshall, C. E., and Patniak, N., 1958. "Ionization of Soils and Soil Colloids, IV: 



Humic and Hymatomelanic Acids and Their Salts," Soil Sci. 75, 153. 



