A microsporangium is generally surrounded by four wall layers - the epidermis, endothecium, middle layers and the tapetum. The outer three wall layers perfom the function of protection and help in dehiscence of anther to release the pollen. The innermost wall layer is the tapetum. It nourishes the developing pollen grains. Cells of the tapetum are food rich and possess dense cytoplasm and generally have more than one nucleus.