This association, better known as coevolution , most likely has driven much of this recent and rapid diversification. Given their agricultural, horticultural, and overall economic importance, it is not surprising that the angiosperms have been the major focus of plant propagators, who have developed numerous propagation techniques. Flowers are where sexual reproduction occurs in angiosperms. Pollination is the transfer of pollen grains from an anther, the structure where these grains are produced, to a stigma, a structure or surface receptive to pollen. If conditions are right, each pollen grain will produce a tube that grows down through the style and into an egg-containing ovule in the ovary, where it deposits two sperm.
Fertilization occurs when a sperm unites with the egg.
In angiosperms, a second remarkable event occurs when the second sperm unites with additional material in the ovary. The ovule, with its now-fertilized egg, develops into a seed, while at the same time the ovary develops into a fruit. Fruits are the vehicles that disseminate or disperse seeds away from the parent plant. Once a seed is released from its fruit, and conditions are favorable for its germination, it can grow into a mature plant that produces its own flowers. Although all angiosperms share this basic life cycle, it is affected in various plants by different factors.