Hoagland — 176 — Plant Nutrition 



dence has been submitted that it has any part in 

 physiological processes. 



I have not been able to leave a clear impression 

 of the functions of potassium in plant metabolism, 

 and aside from the inadequacy of the discussion, this 

 could not be accomplished. At one time or another a 

 role in almost every important physiological process 

 in the plant has been ascribed to potassium. The 

 crucial experiments have not yet been performed that 

 would enable us to say just how potassium enters into 

 varied steps of organic transformations or how it in- 

 fluences the status of protoplasmic colloids. It is at 

 present impossible to state definitely what peculiar 

 chemical properties this element has that makes it 

 indispensable to the physiology of plants and perhaps 

 of all living organisms. 



I have offered this outline primarily for the ob- 

 jective of illustrating the ramifications of research 

 in an attack on any general problem of plant nutrition 

 and the need of many approaches to proceed toward 

 a goal of increased understanding of soil-plant inter- 

 relations. 



REFERENCES :- 



Bray, R. H. and De Turk, E. E. The release of potassium 

 from non-replaceable forms in Illinois soils. Proc. Soil 

 Science Society of America 3 : 101-106, 1938. 



Gregory, F. G. Mineral nutrition of plants. Annual Review 

 Biochemistry VI: 557-578, 1937. 



Hartt, Constance Endicott. Potassium deficiency in sugar 

 cane. Botanical Gazette 88: 229-261, 1929. 



Hoagland, D. R. and Martin, J. C. Absorption of potassium 

 by plants and fixation by the soil in relation to certain 

 methods for estimating available nutrients. Trans, of Third 

 International Congress of Soil Science 1: 99-103, 1935. 



. Absorption of potassium by plants in 



relation to replaceable, non-replaceable, and soil solution 

 potassium. Soil Science 36: 1-33, 1933. 



Jenny, H. and Ayers, A. D. The influence of the degree of 

 saturation of soil colloids on the nutrient intake by roots. 

 Soil Science 48: 443-459, 1939. 



JOFFE, J. S. and KOLODNY, L. The effect of alternate drying 

 and wetting on the base-exchange complex with special 

 reference to behavior of the K-ion. Proc. Soil Science 

 Society 3 : 107-111, 1938. 



Johnston, Earl S. and Hoagland, D. R. Minimum potassium 



