Repeating particles associated with membranes of transfer cells.

Freeze etching of unfixed root nodule transfer cells of Trifolium repens reveals regular arrays of 11 nm particles on the fracture face of the plasmalemma associated with wall ingrowths. The particles are arranged in a hexagonal lattice and have a centre-to-centre spacing of 15 nm. Similarly arranged, smaller particles also occur on the bacteroid membrane envelopes.