in order that the plant may assimilate its nitrogen. 

 The process (osmosis) by which nutrients pass 

 through the plant from cell to cell is facilitated by 

 the presence of phosphoric acid. Phosphorus is nec- 

 essary for the seed's embryo development and for the 

 formation of chlorophyll (the green coloring matter 

 of plants). 



Thus, while the essential plant foods each have 

 many independent functions to perform, they are 

 mutually dependent upon each other, and mutually 

 helpful in the building of the plant tissue. 



The condition of the soil may be such that the 

 purchase of only one fertilizing element is necessary, 

 and since the sources of nitrogen and phosphoric 

 acid and their functions are so many and varied, the 

 question, " What fertilizer to use," and " How to pur- 

 chase it most economically," is of vital interest to 

 the farmer and one difficult to solve. 



SOURCE OF FERTILIZERS. 



THE SOURCES OF NITROGEN. 



Nitrogen may be obtained from these sources : 

 Air, ammonia, nitrates and animal matter. In cer- 

 tain forms of animal matter, such as hoofs, horns, 

 coarse bone, leather and wool waste, the nitrogen 

 becomes available too slowly to be of much value. 

 But as green manure, ammonia, nitrates, blood, fine 



8 



