Development of 3 celled pollen grain :
(i) Every cell of the sporogenous tissue has a potential pollen mother cell (PMC) and can give rise to microspore tetrad or pollen grains.
(ii) Each microspore mother cell undergoes meiosis to form a cluster of four haploid cells, called microspore tetrad.
(iii) As the anther matures, the microspores dissociate from the tetrad and develop into pollen grains.
(iv) The nucleus of the microspore undergoes mitosis to form a large vegetative cell or tube cells and a small spindle-shaped generative cell that floats in the cytoplasm of the vegetative cell.
(v) They develop a two-layered wall, the outer exine made of sporopollenin and the inner intine made of cellulose and pectin.
(vi) Usually, the pollen grains are liberated at this two-celled stage. In certain species, the generative cell divides mitotically to form two male-gametes, and the pollen grains are three called during liberation.
