repulsion theory

(field theory) The theory that the pattern of origin of leaf primordia at the shoot apex is regulated physiologically by inhibitory substances synthesized by the apex and the older primordia. A new primordium arises in a position where the concentration of these substances has fallen below a certain threshold level. Although no such inhibitors have yet been isolated various surgical and modelling experiments support the theory. Compare available space theory. See also phyllotaxis.