Clonal analysis provides evidence for transient initial cells in shoot apical meristems of seed plants

Drift of mutated sectors in sectorial or mericlinal plant chimeras has been interpreted as indirect evidence of initial impermanence at the apex. Howe ver, the same effect may result from mutation in noninitial cells positione d close to the vertex of the apical dome. Clonal analysis of the cell packe ts present in the superficial layer of spruce and magnolia apices provided the library of patterns suggesting that the position and the number of init ial cells, and in some cases also the meristem axis inclination, may change over time. Multicellular clones originating from a single cell have been f ound in the geometric center of some spices, whereas in other apices the ce llular center (where three or four clonal borders meet) did not correspond to the geometric center of the apex. Such effects may result only from init ial impermanence.