Fig. 3. Isolation of shoot meristem stem cell mutants in Arabidopsis. In this model of shoot meristem initiation, the first leaf primordia (green) arise before the central cells appear to be specified (red), whereas subsequent leaves are derived from the stem cells. Mutations affecting partitioning of the shoot meristem primordium could result in an altered size of the stem cell region, represented by stm (with fused organ primordia, arrow) and clv (with an increased meristem, arrow) mutants. Mutations affecting stem cell specification would result in altered cells in the center but normal first leaves, represented by a wus seedling.