XVI International Botanical Congess

Sectioned young tassels revealed relationships between the developing vascular system and the placement of lateral primordia. Gradual suppression of leaf development in the transition region: decreased internode elongation, reduced procambial development, limited bud development, and reduced marginal collar growth, were associated with the shift from distichy to polystichy. Procambium differentiated in isolation but associated with lateral tassel primordia. Adjacent traces linked to form sympodia which joined earlier established sympodia. The observed patterns explain the transition from two ranked vegetative leaves to four ranked spikelet pairs in the maize central tassel spike. They also provide insight into the evolution of the multiple-ranked maize ear from a two-ranked lateral bud.