Angiosperms are highly developed plants that reproduce by flowering and producing seed; they beautify our gardens and fill our kitchens with food. The seeds produced by flowering and fruiting plants accomplish more, though, than to simply reproduce their parent plant.
Seeds are the product of sexual or asexual reproduction in plants. They grow in ovaries or fruits as the result of fertilization, often with the help of insects such as bees or birds such as hummingbirds.
The primary function of seeds is the continuation of the species. This is especially important for annual plants that do not reproduce easily by division.
The earliest land plants propagated by means of spores--single-celled reproductive bodies. As plants became more diverse and complex, seeds evolved, first as soft-sided seeds on gymnosperms and then as the hard-coated angiosperm seed, with embryo and food supply.
Seed production provides an opportunity for a species to improve itself by hybridization. Pollen from another species is used to fertilize an egg and the seed that develops will contain an embryo of an improved or stronger new species.
As long as the plant works on producing seed or blooms or fruits are removed, the plant will continue to work, growing ever less vital. The maturation of seeds provides signals to the plant that the end is near and to begin the process of dying back so seeds can mature and fall.