Germ cells differ from somatic cells in their chromosomal complement, being haploid rather than diploid. In animals, the germ cells are generally produced by a separate lineage set aside early in development. Plants, however, lack a reserved germ cell lineage. Kelliher and Walbot (see the Perspective by Whipple) now show that, in maize, the key signal for germ cell production is hypoxia, which triggers differentiation of anther germ cells from a generalized field of progenitors. The specializing germ cells then induce differentiation of supportive somatic cells.