The stages involved are microsporogenesis, arrangement into tetrad, mitosis and rounding off of angiosperm Pollen. In microsporogenesis, the reductional division occurs and leads to the formation of four microspores. Next, these microspores arrange themselves in a tetrad shape, and then mitosis occurs inside the microsporangium to form microspores. These microspores are now known as Pollen grains, and they get a circular shape and then released into the atmosphere in the final rounding off stage, which is known as dehiscence. These pollen parts form a thick wall around them which differentiates them into individual grains. These are the stages involved in the maturity of a microspore into a pollen grain.