Shoots and nitrogen-fixing nodules. Two shoots (white) sprouting from a root system that has numerous nitrogen-fixing nodules (rounded protuberances). Nodules of this type are produced by species of Rhizobium bacteria in the soil entering the roots of leguminous plants. The bacterium benefits from a safe environment within the plant, and the plant benefits from the bacterial ability to fix atmospheric nitrogen within the nodule. This is an example of symbiosis. These roots are part of a Thermopsis rhombifolia flowering plant, found in the USA from the Rocky Mountains to New Mexico.