a. Development of female gametophyte : The female reproductive part of a flower is gynoecium,which consists of three parts - stigma, style and ovary.The ovules are formed in the ovary and attaches to it through placenta.The ovary is surrounded by 1-2 protective layers called integuments,leaving a small opening at one end termed as a micropyle.The stalk of the ovule is funiculus.The ovule is composed of multi layered cellular tissue called the nucellus.A hypodermal cell of nucellus enlarges and becomes a megaspore mother cell that undergoes meiosis to form a tetrad of megaspore.Out of four, only one remains functional and three megaspores degenerate.The functional megaspore undergoes three divisions to form eight nuclei,which arrange themselves into three groups. The three nuclei migrate at micropylar end and form the egg apparatus. The other three nuclei from antipodal cells at chalazal end.The remaining two nuclei come together as polar nuclei in the cnetre of the embryo sac.
b. Role of endothecium : Microsporangium generallu syrrounded by four wall layers epidermis,endothecium,middle layer and the tapetum.Endothecium perform the function of protection and help indehiscnece of anther to release the pollen. The outer three layers epidermis, endothecium and middle layer,give protection and help in dehiscence of anther to release the pollen.
Role of taoetum : It nourishes the developing pollen grain.