From WebRef.org
Jump to: navigation, search

those capable of combining free nitrogen of the air with oxygen, either in the nodules of the roots of leguminous plants (such as clover, peas, alfalfa, etc.), or by other species of bacteria that live freely in the soil (nonsymbiotic nitrogen-fixation)

Source: Noland, George B. 1983. General Biology, 11th Edition. St. Louis, MO. C. V. Mosby