82 



THE VEGETATIVE FUNCTIONS OF PLANTS 



potassium, calcium, magnesium, ammonium, and others, 

 forming potassium nitrate (KNOs), calcium nitrate 

 (Ca(N03)2), ammonium nitrate (NH^NOs, and so forth. 

 Nitrates and ammonia may result from the disintegration 

 of plant and animal bodies, but the supply must con- 

 tinually be renewed by drawing upon the free nitrogen 



FIG. 6 1. Root-tubercles on yellow sweet clover (Melilotus liUea), caused 

 by and containing Pseudomonas radicicola. 



of the air. Ammonia results chiefly from the decom- 

 position of plants and animals, and for the formation of 

 nitrates we are chiefly dependent upon non-green plants, 

 including certain bacteria and fungi. Two important 

 nitrogen-fixing bacteria live in the soil ; one (Nitrosomonas) 



