Question

With the help of suitable diagram describe the structure of pollen sac.

Accepted Answer

The pollen sac or microsporangium is a cylindrical sac which appears circular in transverse section, located in the anther. It consists of two parts: a) Pollen sac wall and b) Sporogenous cells.

(a) Pollen sac wall: It has four types of layers: (i) Epidermis (ii) Endothecium (iii) Middle layers and (iv)Tapetum.

(i) Epidermis: It is the outermost part of a pollen sac, which is a single layer and gives protection to the pollen sac.
(ii) Endothecium: This layer lies just below the epidermis and composed of single layer of cells. The cells of endothecium are thick and radially elongated. These cells are of hygroscopic in nature and during dry conditions, due to pulling, tension is produced in these cells which results in the dehiscence of the pollen sac.
(iii) Middle layers: One to three layers of cells, just inside the endothecium form the middle layers.
(iv) Tapetum: This is the innermost layer of the pollen sac wall and forms a single layer around the sporogenous tissue. It provides nourishment to the developing pollen grains.

(b) Sporogenous tissue: The group of diploid cells in the pollen sac, surrounded by the wall layer is known as sporogenous tissue. These cells give rise to form microspore mother cells and that undergo meiosis to form microspores or pollen grains.

With the help of suitable diagram describe the structure of pollen sac.

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