In the next sections, we discuss the following questions: What is the genetic basis of secondary meristem regulation and how are environmental inputs integrated? Is there
coordination of the regulation of different types of secondary
meristems? To what extent does the differential activity of
secondary meristems contribute to the establishment of different plant growth forms? Here, we summarize knowledge of the regulation of AMs and the vascular cambium in the shoot, and discuss the potential of secondary meristems to serve as a model for addressing the role of phenotypic plasticity, in this case morphological plasticity, during evolution.