Root border cells (RBC) formerly called dead sloughed root cap cells are live cells released to soil by the growing root from the outermost cap layer. They differ from root tip cells in morphology, pattern of synthesized proteins and function. The number of RBC produced by a given root during a 24-h period is conserved at the family level. Production and RBC release from the root cap is controlled by endo- genous signals and many environmental factors.