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
Gum (botany) Gum (botany) Gum is a sap or other resinous material associated with certain species of the plant kingdom. This material is often polysaccharide-based and is most frequently associated with woody plants, particularly under the bark or as a seed coating. The polysaccharide material is typically of high molecular weight and most often highly hydrophilic or hydrocolloidal. Many gums occur as seed coatings for plant species; the adaptive purpose of some of these gummy coatings is to delay germination of certain flora seeds. An example of such a gummy coating occurs in the case of Western poison oak, a widespread shrub