Individual plants are either male producing microspores or female producing megaspores. Conifers are heterosporous, generating two different types of spores&colon; male microspores and female megaspores. The microspores become microgametophytes (pollen). These plants have two spore types, megaspores and microspores. These support the development of microspores into mature pollen grains. Each of the microsporocytes in the microsporangia undergoes meiosis, producing four haploid microspores. Microsporangia are sporangia that produce microspores that give rise to male gametophytes when they germinate. These microspores undergo meiosis to form a flagellated sperm. The microsporangia produce the microspores, which for seed plants are known as pollen grains. According to Maraschin et al., androgenesis must be triggered during the asymmetric division of microspores. The microspores develop into pollen grains, which are male gametophytes. Microspores produce microgametophytes which the produce sperm. During microgametogenesis, the unicellular microspores undergo mitosis and develop into mature microgametophytes containing the gametes. The septa are perforated by microspores, arranged in a ring structure. Pollen grains (microgametophytes) mature from microspores, and ultimately produce sperm cells.