Step 1: Understanding microsporangium.
The microsporangium is a structure present in the anther of a flower where pollen grains are produced. Inside the microsporangium, several layers of cells are present that help in the development of microspores (pollen grains). The innermost layer of these wall layers is called the tapetum. This layer plays a very important role in the formation and nourishment of pollen grains.
Step 2: Structure and position of tapetum.
The tapetum is the innermost layer of the microsporangium wall and lies just outside the sporogenous tissue. The cells of the tapetum are usually large, dense, and rich in nutrients. These cells may contain more than one nucleus and are metabolically very active. Because of their position and structure, they are well suited to support the development of pollen grains.
Step 3: Nourishment of developing pollen grains.
One of the most important functions of the tapetum is to provide nutrition to the developing microspores and pollen grains. During the process of microsporogenesis and pollen development, the tapetal cells supply essential nutrients, enzymes, and other materials that are required for proper growth and maturation of pollen.
Step 4: Formation of pollen wall materials.
The tapetum also plays a crucial role in the formation of the outer wall of pollen grains known as the exine. It produces substances such as sporopollenin precursors and other materials that contribute to the development of the pollen wall. Sporopollenin is a highly resistant substance that protects pollen grains from environmental damage.
Step 5: Secretion of important substances.
Tapetal cells secrete several important substances including enzymes, proteins, lipids, and hormones that help in the development and maturation of pollen grains. In many plants, the tapetum eventually degenerates after completing its function, releasing these substances into the microsporangium to support pollen development.
Final Answer:
The tapetum is the innermost nutritive layer of the microsporangium that provides nourishment to developing pollen grains and helps in the formation of the pollen wall by supplying essential materials and enzymes required for proper pollen development.