The development of angiosperm gametophytes

Pollen grains are the immature male gametophytes produced by flowers and trees, or more precisely, the seed plants. In seed plants the seed and the pollen grain replaces the spores as a mode of dispersing the offspring. All seed plants are heterosporous, meaning they have two different types of sporangia to produce two types of spores: megasporongia produce megaspores, which give rise to the female gametophytes, whereas the microsporongia produce microspores, which give rise to male (sperm-containing) gametophyte. Microspores develop into pollen grains, which in turn mature to become the male gametophytes of seed plants.