Rhizobium is found in the root nodules of the leguminous plants .Explain it and its functions also define root nodules........

Solution:

Root nodules are the infected root hair and other root tissues of leguminous plants such as pea that contain Rhizobium for biological nitrogen fixation. Rhizobium in return takes food and shelter from plant.  

Leguminous plants develop root nodules in response to infection by a specific genus of bacteria named Rhizobium. The nodules produce a molecule similar to haemoglobin in structure called leghaemoglobin, which is pink in colour. The leghaemoglobin acts as a carrier for nitrogen molecules and helps in it's fixation from the atmosphere via the roots in the plant.
Thus root nodules are important for the plant to fix the atmospheric nitrogen.