http://www.ibioseminars.org/lectures/bio-mechanisms/sharon-long.html
Legume plants form specialized root nodules to host "rhizobia", nitrogen-fixing bacterial symbionts. Plants which can host symbiotic nitrogen fixing rhizobia are able to grow without exogenous nitrogen fertilizer. This allows legumes to be high in protein and to provide nutrition to surrounding plants. Genetic, molecular and cell biology approaches show that this process is quite complex and is governed in part by an exchange of chemical signals.
