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
Compartmentalization of decay in trees compartmentalization. According to CODIT, when a tree is wounded cells undergo changes to form "walls" around the wound, slowing or preventing the spread of disease and decay to the rest of the tree. By increasing understanding of how trees respond to decay, CODIT has had many applications. For example, arborists are frequently called upon to analyze the danger posed to people or property by a damaged or decaying tree. By knowing how decay is likely to spread, such hazard tree analyses may be more accurate, thereby preventing unnecessary tree removal, property damage, or injury. For another example, in the production