Abstract

A geometrical model is proposed that describes the emergence of a primordium at the shoot apex in Dicotyledons. It is based on recent fundamental results on plant morphogenesis, viz.:the emergence is preceded by the reorganization of the microtubules of the cortical cytoskeleton, leading to a new orientation of the synthesis of the cell wall microfibrils;the resulting global stress is related to the general orientation of the cell growth;The model sums up the continuous interactions that link the microtubules, the microfibrils and the cell growth axis.The paper tries to answer three essential questions:Why does the principal stem shifts its growth direction after each lateral emergence?Why do the three axes involved in any ramification exhibit a plane configuration whereas this is an essentially three dimensional phenomenon?Does phyllotaxis exclusively depend upon the local emergence of a primordium?An interactive procedure between empirical botanical knowledge and the mathematical model leads to an insight of the compatibility mechanisms that link the various microtubules and microfibrils networks, and the apical dome restoration.A geometrical formalism allows a redefinition of both the “generating centre” and the “organizing centre”, and their field effect