Polyandrous condition (having large and indefinite number of stamens) is present in Gloriosa (family liliaceae) and Petunia (family solanaceae). Nitrogen fixation is the conversion of inert atmospheric nitrogen into utilisable compounds of nitrogen like nitrate, ammonia, amino acids, etc. Biological nitrogen fixation is performed by free living and symbiotic bacteria and cyanobacteria. Symbiotic nitrogen fixers occur in association with roots of higher plants. For e.g., Rhizobium is nitrogen fixing bacterial symbiont of papilionaceous roots and Frankia is symbiont in root nodules of several nonleguminous plants like Casuarina. Both Rhizobium and Frankia live free as aerobes in the soil and develop the ability to fix nitrogen only as symbionts when they become anaerobic.