ELEMENTS NECESSARY FOR PLANT GROWTH 37 



plant, with water. During this process, oxygen is given 

 off from the plant. 



32. Nitrogen. When pure, nitrogen is a colorless, 



FIG 9. Roots of red clover showing nodules by which nitrogen is 

 secured for the plant. 



odorless, tasteless and very inactive gas. It combines 

 directly with but few elements, although indirectly it enters 

 into the formation of a large number of compounds possess- 



