Sexual Reproduction:- Biology
Sexual Reproduction:
It involves fusion of two compatible gametes or sex cells. All organisms reach to the maturity in their life before they can reproduce sexually. In plants, the end of juvenile or vegetative phase marks the begining of the reproductive phase and can be seen easily in the higher plants at the time of flowering.
The flower is specialized reproductive structure of a plant in which sexual reproduction takes place. The function of flower is to produce haploid gametes and to ensure that fertilization will take place. Typical flower consists of four different whorls viz. calyx, corolla, androecium and gynoecium.
Structure of Anther :
Anther is generally dithecous (having two lobes) and tetrasporongiate. Each lobe of anther contains two pollen sacs. In dithecous anther four pollen sacs are present. Therefore, it is tetrasporongiate. An immature stage of anther is represented by group of parenchymatous tissue surrounded by single layered epidermis. The heterogenesity (differenciation) arises when some hypodermal cells get transformed into archesporial cells.
T. S. of Anther :
The archesporial cell divides into an inner sporogenous cell and outer primary parietal cell. Sporogenous cell forms sporogenous tissue. Each cell of sporogenous tissue is capable of giving rise to a microspore tetrad. Parietal cell undergoes divisions to form anther wall layers. The wall of mature anther consists of four layers. Epidermis is the outermost protective layer made up of tabular (flattened) cells. Endothecium is sub-epidermal layer made up of radially elongated cells with fibrous thickenings. Inner to endothecium is middle layer made up of thin walled cells (1-2 layered), which may disintegrate in mature anther. Tapetum is the inner most nutritive layer of anther wall. It immediately encloses the sporogenous tissue (microspore mother cells).
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