Legume Nodule Morphology with Regard to Oxygen Diffusion and Nitrogen Fixation

Soybean (Gtycine max (L.) Merr. cv. Fiskeby V), white clover (Trifolium repens L. cv Blanca) and lucerne (Medicago sativa L.cv. Europe) nodules grown in fluid culture of Perlite were examined by cryo-scanning electron microscopy. The surfaces of all three species consisted of loosely packed cortical cells, collapsed areas covering intact cells and in soybean, troughs which lacked the layers of loosely packed cells and were covered by an amorphous matrix. The superficial cortical cells were hydrophobic and their surfaces were covered by a solvent-extractable stippling. This stippling was absent from the surfaces of underlying cells. Air-filled intercellular spaces in fractured nodules were seen throughout the cross-section.