Bacteria inside root nodules need oxygen to survive. A pink or red color inside a nodule indicates the oxygen supply is robust and the bacteria are thriving. Disclaimer: AAAS and EurekAlert!

IN addition to the red pigment, hæmoglobin,· we have always found in leguminous root nodules a brown pigment. This is methæmoglobin with trivalent iron1. The simplest way of demonstrating its ...