Fig. 9. Model for a conserved NS/PRS function during the recruitment of a lateral founder-cell domain in vegetative (A,B) and reproductive (C) shoot meristems of maize (A) and Arabidopsis (B,C). NS/PRS function initiates from lateral foci (red arrows) and recruits founder cells in a lateral meristematic domain (yellow). Recruitment of the central domain founder cells (green) occurs prior to recruitment of the lateral domain. In vegetative apices that produce a single leaf per node, recruitment of the central founder-cell domain occurs from a single flank of the apex and proceeds bi-directionally toward the lateral domain foci, whereas in the Arabidopsis floral meristem this recruitment commences simultaneously from both the adaxial and abaxial flanks of the apex. Loss of NS/PRS function causes failure to develop any and all organ domains that are normally derived from the lateral founder-cell domain of the meristem. Further details of this organ domain-blind model of NS/PRS are explained in the text.