question_answer 70)

  Draw the diagram of a microsporangium and label its wall layers. Write briefly about the wall layers?

Answer:

                  The diagram representation of amicrosporangium is shown below     (a) Transverse section of a young anther (b) Enlarged view of one microsporangium showing wall layers (c) Mature dehisced anther showing pollen grain   In a transverse section, a typicalmicrosporangium is circular in outline and is surrounded byfour wall layers. (a) Epidermis The epidermis is the outermost protective layer. It is composed oftangentially flattened cells. The cells are closely fitted and have thick walls which ishelpful in the dehiscence of anther. (b) EndotheciumIt is present below the epidermis and expands radically with fibrous'thickenings, at maturity these cells loose water, at contract and help in dehiscence ofpollen sac. (c) Wall Layersit is present between well marked endothecium and tapetum. These arethin walled layers, arranged in one to five layers, which also help in dehiscence ofanther. (d) TapetumIt is the innermost wall layer with large cells, thin cell walls, abundantcytoplasm and have more than one nuclei. Tapetum is a nutritive tissue whichnourishes the developing pollen grains.The centre of the microsporangium consists of sporogenous tissue, which undergoes meiotic divisions to form microspore tetrads. This process is known asmicrosporogenesis.