Spatial organization of grains reflecting the morphogenesis of the ear. The grains are arranged in rings and rows. Each ring corresponds to a cohort of organs with synchronous development, while a developmental gradient exists between cohorts depending on their vertical position along the rows. Floret cohorts are initiated sequentially at the ear apex. The oldest cohorts are located at basal positions and the youngest at apical positions. A, B Under optimal conditions, pollination and fertilization follow the order of silk emergence which is illustrated by colors: zone 1 cohorts (blue) are fertilized first, followed by zone 2 (green), zone 3 (yellow) and zone 4 (red). (C–E) Abiotic stresses occurring at flowering induce abortion that preferentially affects the youngest apical cohorts in zone 4, followed by the basal cohorts. E, F Severe constraints affecting pollination (pollen availability or viability) result in a wide variety of phenotypes characterized by incomplete cohorts and erratic cohort numbers.