Pollen (microsporocyte, pollen mother cell or meiocyte), after meiotic division. After the formation of the four microspores, which are contained by callose walls, the development of the pollen grain walls begins. The callose wall is broken down by an enzyme called callase and the freed pollen grains grow in size and develop their characteristic shape and form a resistant outer wall called the exine and an inner wall called the intine. The exine is what is preserved in the fossil record. Two basic types of microsporogenesis are recognised, simultaneous and successive. In simultaneous microsporogenesis meiotic steps I and II are completed
Annulus (botany) dissolve to allow the cap to fall off and the spores to be released. Annulus (botany) An annulus in botany is an arc or a ring of specialized cells on the sporangium. These cells are arranged in a single row, and are associated with the release or dispersal of spores. In leptosporangiate ferns, the annulus located on the outer rim of the sporangium and serves in spore dispersal. It consists typically of a ring or belt of dead water-filled cells with differentially thickened cell walls that stretches about two-thirds around each sporangium in leptosporangiate ferns. The thinner walls on the