82 
THE VEGETATIVE FUNCTIONS OF PLANTS 
potassium, calcium, magnesium, ammonium, and others, 
forming potassium nitrate (KNOs), calcium nitrate 
(Ca(NOs)2), ammonium nitrate (NH 4 )N03, 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. 61. Root-tubercles on yellow sweet clover (Mdilolus lutea), 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) 
