A double flower of the snowdrop, Galanthus nivalis. The picture shows petals, green and white, at the centre of the flower. The yellow masses are abnormally developed anthers at the edges of the petals.Single flowers develop under the control of a succession of genes, designated the ABC pathway. In normal development, this gives rise to concentric layers of different tissues; sepals enclose the flower bud, with a ring of petals as the next layer, then anthers, with the female tissue at the centre of the flower. In double flowers, this pathway is disrupted; the cells that would have produced the anthers produce petals. This process is imperfect, with the result seen here - a partial conversion, with anther-like tissue attached to petal-like blades. Such flowers are infertile. and persist for longer on the plant, a benefit for garden display.