The proliferation of populations of cells in root apices was simulated using a model based on data for cell lengths in the growth zone of seedling roots of Zea mays L. Two different bases were used for defining cell populations. Cells in ‘r-populations’ lie between apical and basal bounds which move through the growth zone. Proliferation of these cells involves immigration over the apical bound and emigration over the basal bound. Cells in a ‘p-population’ lie between specified sets of cross walls, and proliferate without emigration or immigration. In both cases, cell populations were initially composed entirely of proliferative cells, but these were replaced gradually by non-proliferative cells. Cell cycle durations decreased as the cells moved through the meristem. The populations were made up of cells of a number of generations at any time. Positive correlations were found between sibling cell cycle durations, and negative correlations between mother and daughter cell cycle durations. These results are compared with observed data, and relationships between the structure of the model and observed features of cell proliferation in roots are discussed.