Pre-fertilization Structure and Events

Pre-fertilization events begin well before a flower opens, with hormonal and structural changes in the growing shoot that differentiate a floral primordium and drive it to mature into a complete flower. As already introduced, the androecium (stamens) is the flower's male reproductive whorl and the gynoecium (one or more pistils, each built from a carpel) is its female reproductive whorl, arranged around the pedicel along with the protective sepals and the attractive petals, with the ovary at the pistil's base enclosing the ovule(s) and the stigma at its tip serving as the landing platform for pollen. The structures and events that must take place before fertilization, in order, are: full differentiation and maturation of the anther, culminating in pollen grains that carry the male gametophyte; full differentiation and maturation of the ovule, culminating in an embryo sac that carries the female gametophyte; and pollination, the mechanical transfer of mature pollen from an anther to a receptive sti …