INTRODUCTION 



but it was not until 10 years later that the importance of nitrate as 

 a plant nutrient was generally accepted. With this advance, the role 

 of the soil as a source of inorganic salts for plants was firmly 

 established. 



B. Salt Content of Plants 



The results of an ash analysis of a Zea mays plant are shown in 

 Table 2. It can be seen that the elements present, excluding carbon. 



Table 2. Mineral Content of a Zea mays (Pride of Saline) Plant grown at 



Manhattan, Kansas, in 1920 

 (From Miller, 1938) 



hydrogen and oxygen, comprise a rather small percentage of the 

 total dry weight, and more than half of this is made up of nitrogen, 

 silicon and potassium. Most of the nitrogen and phosphorus in 

 plants is present in organic compounds, while some of the other 

 elements occur partly in this form. The bulk of each metallic 

 element, however, exists as inorganic compounds or ions, and much 

 of it is dissolved in the aqueous sap of cell vacuoles. 



Plants are invariably rich in potassium, and the name, derived 

 from "pot-ashes", commemorates an early method of preparing 

 potassium salts. In contrast, aluminium is found in relatively small 

 amounts in many plants, although it is an abundant constituent of 

 soil. A few species contain large amounts of this element, notably 



