‘Organs’ considers organogenesis — organ development, which involves large numbers of genes. Pattern formation in development in a variety of organs can be specified by positional information, which is specified by a gradient in some property. Examples include mammalian limb development, adult organs and appendages of the fly, the development of compound eyes in insects and the vertebrate eye, and the vascular system. Flower development is also discussed. Flowers contain the reproductive cells of higher plants and the individual parts of a flower — sepals, petals, stamens, and carpels — each develop from a floral organ primordium produced by the floral meristem.