Root Nodules (IMAGE) Norwich BioScience Institutes Caption This is a magnified image of nodules on the root of Medicago. Nodules house the symbiotic bacteria key to the nitrogen fixation process. Credit Andrew Davis, John Innes Centre Usage Restrictions Please credit the John Innes Centre. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.