In the structure of a microsporangium, which layer is the innermost one and responsible for nourishing the developing pollen grains?

The tapetum, a somatic cell layer neighboring the developing male meiocytes, serves a vital function in pollen development. During the initial stage of anther development, tapetal cells release nutrients, proteins, lipids, and enzymes to support microsporocyte and microspore development. Subsequently, they undergo programmed cell death in the later stage, contributing essential materials for the formation of the pollen wall.