176 SCIENTIFIC AGRICULTURE. 



First, the soil serves as the foundation for upholding and 

 giving mechanical support to the vegetable structure. 



Secondly, it absorbs light, heat, air and moisture, which are 

 indispensable to healthy vegetation. 



Thirdly, it supplies both the organic and inorganic elements 

 required by the plant as food. 



Fourthly, it is a chemical laboratory, in which these ele- 

 ments are constantly being prepared to be taken into the plant 

 by its roots. 



