The tissue that makes up the greater part of the ovule (multilayered body of ovule) is called nucellus. It has abundant food reserves and therefore act as nutritive tissue for the embryo in some plants. One of the cells of the nucellus differentiates and acts as a megaspore mother cell (MMC).

Differentiate between microsporogenesis and megasporogenesis.

Features Microsporogenesis Megasporogenesis Definition Microsporogenesis involves the formation of microspores from microspore mother cells by meiotic division. Megasporogenesis is the process of formation of megaspores from the megaspore mother cell. Occurrence It occurs inside the pollen sac of the anther. It occurs in the ovule of the ovary. Number of spores produced In microsporogenesis, four microspores are produced from each microsporocyte cell. Megasporogenesis results in the formation of a single functional megaspore from each megasporocyte cell. The other three megaspores usually degenerate and do not contribute to female gametophyte formation. Function and Development: Microspores produced during microsporogenesis develop into pollen grains, which contain the male gametophyte. These pollen grains are eventually released and transported to the female reproductive organ for fertilization. The surviving megaspore formed during megasporogenesis undergoes subsequent development to form the female gametophyte (embryo sac). The female gametophyte contains the egg cell and other cells necessary for fertilization and embryo formation.