Flower Structure

Structure of the Flower The floral meristem differentiates into four concentric groups of cells that form the four parts of the flower. The cells in whorl 1 develop into a whorl of sepals. These form at the lowest level. Collectively they make up the calyx. Whorl 2 forms above the calyx, forming the petals. Collectively these make up the corolla of the flower (the part that most ornamentals are grown for). Whorl 3 develops into the stamens, the male reproductive organs. The innermost whorl, 4, forms carpels, the female reproductive organs. Carpels often fuse to form a single structure, which some botanists call the pistil. What triggers the various parts of the floral meristem to enter one or another of these four developmental pathways?