Draw the diagram of microsporangium of an Angiosperm and label any four parts. State the function of its innermost wall layer.

A typical microsporangium appears near circular in the outline in its transverse section It is made up of four layers namely:

Epidermis.

Endothecium

Middle layers

Tapetum

Epidermis, endothecium and middle layers are protective in function and help in dehiscence of another. The innermost layer is tapetum which nourishes the developing pollen grain. Cells of the tapetum possess dense cytoplasm and generally have more than one nucleus. Tapetal cells can also become binucleate or multinucleate by undergoing endomitosis. In endomitosis, nucleus divides within the nuclear membrane but cytokinesis does not occur.