Lateral fusion of membranes in bacteroid-containing cells of leguminous root nodules

Bacteroid-containing cells of leguminous root nodules (Pisum and Trifolium) provide an environment in which the membrane envelope surrounding each bacteroid can exhibit unusual properties. The bacteroids are crowded, and frequently neighbouring membrane envelopes come into close contact. In such cases the two envelopes can fuse laterally to give a symmetrical tripartite membrane, probably consisting of a composite inner layer sandwiched between the outer leaflets of the two parent membranes. The expanse of fused membrane forks at its periphery, i.e is confluent with both of the envelopes from which it is derived, and seems to be relatively stable.