It is the change from a vegetative apical meristem to a reproductive apical meristem.
Some observeable panicle characteristics are the panicle type, the secondary branching of the panicle, the panicle axis and the panicle exsertion.
Division: a) type are compact, intermediate, open; b) secondary branching are absent, light, heavy, clustering; c) axis are droopy, straight; d) exertion are well exerted, moderately well exerted, just exerted, partly exerted, enclosed.