POSTEMBRYONIC development in plants is achieved by apical meristems. Surgical studies and clonal analysis have revealed indirectly that cells in shoot meristems have no predictable destiny1–3 and that position is likely to play a role in the acquisition of cell identity4–7. In contrast to animal systems8–10, there has been no direct evidence for inductive signalling in plants until now. Here we present evidence for such signalling using laser ablation of cells in the root meristem of Arabidopsis thaliana. Although these cells show rigid clonal relationships11, we now demonstrate that it is positional control that is most important in the determination of cell fate. Positional signals can be perpetuated from more mature to initial cells to guide the pattern of meristem cell differentiation. This offers an alternative to the general opinion that meristems are the source of patterning information12.