Several lines of evidence suggest that root and shoot apical meristems are related evolutionary modifications of an ancestral meristem. Mutations that affect the development of both shoot and root meristems may therefore represent genes whose functions have been conserved throughout apical meristem evolution. On pages 877887 of this issue, Keddie et al. describe one such gene, the Defective embryo and meristems (Dem) gene of tomato, which is required for correct cotyledon initiation during embryogenesis and for the development of both shoot and root apical meristems. Although the Dem sequence does not help the authors to define its role in meristem development‹it encodes a protein with marked similarity to a yeast protein of unknown function‹they postulate that Dem may be necessary for the organized cell divisions that occur in meristems and organ primordia. One efffect of mutations in Dem is shown on the cover: this 6-week-old dem mutant seedling has three cotyledons.