CHAPTER 



I O Growth and Function as 

 Criteria in Determining 

 the Essential Nature of 

 Inorganic Nutrients 



DANIEL I. ARNON 



T 



he knowledge of what inorganic elements are indis- 

 pensable for the growth of green plants is obviously of fundamental 

 importance in plant nutrition. Certain inorganic elements are es- 

 sential for the life of all living forms, but, in the case of plants, 

 inorganic or, as it has been traditionally known, mineral nutrition 

 looms particularly large. Among the multitude of life forms, auto- 

 trophic plants are, except for certain bacteria, the only organisms capable 

 of synthesizing all of their food requirements for maintenance, growth, 

 and reproduction if supplied with the mineral essentials including water 

 and carbon dioxide. 



How can the mineral requirements of plants be determined? More 

 specifically, what inorganic elements are essential for the growth of 

 higher plants grown in soil? The present discussion will concern 

 itself with this latter question. No attempt will be made to survey the 

 kindred field of inorganic requirements of lower plant forms or of 

 animals, except in so far as some considerations pertinent to green 

 plants apply to other organisms as well. 



The natural soil medium for the growth of higher plants is an 

 extraordinarily complex physical, chemical, and biological system. 

 Its suitability for plant growth is determined by a proper interaction 

 of the various soil factors to make available to the plant a continuous 

 and adequate supply of essential inorganic nutrients. To answer 



