Which layer of microsporangium is nutritive in function?

The correct answer is Option (4): Tapetum

In a transverse section, a typical microsporangium appears near circular in outline. It is generally surrounded by four wall layers – the epidermis, endothecium, middle layers and the tapetum.

The outer three wall layers perform the function of protection and help in the dehiscence of anther to release the pollen. The innermost wall layer is the tapetum. It nourishes the developing pollen grains. Cells of the tapetum possess dense cytoplasm and generally have more than one nucleus.