INTRODUCTION 



49 



Phosphorus, and Iron are necessary to the growth 

 of a plant, with also the carbon, hydrogen and 

 oxygen obtained from the carbon dioxide of the 

 atmosphere and water. Sulphur is also an important 

 element. If iron is omitted there is no formation 

 of chlorophyll, and without the latter no photo- 

 synthesis of carbon. 



The table given below, compiled by Warington, 

 shows the relative proportion of the substances 

 found in the ash of different parts of plants. 



If single salts are employed they may have a toxic 

 or harmful effect. But the mixture of several salts is 



