Pollen grain (male gametophyte)
(i) The pollen grains represent the first cell of male gametophytes.
(ii) A pollen grain has a two-layered wall namely,
Exine: it is the hard outer layer which is made up of sporopollenin.
(i) It is the inner, thin and continuous layer which is made up of cellulose and Pectin.
(ii) A mature pollen grain contains two cells namely,
(c) Vegetative cell
(d) Generative cell
Vegetative cell :
It is bigger ceil having abundant food reserve and a large irregularly shaped nucleus.
Generative cell :
(i) It is small cell that floats in the cytoplasm of the vegetative cell.
(ii) It is spindle-shaped with dense cytoplasm and a nucleus.
1. The pollen grains are shed at the 2-celled stage in Flowering Plants.
2. ln other plants, the generative cell divides mitotically to give rise to the two male Sometimes before pollen grains are shed in 3-celled stage.
3. Once they are shed, pollen grains have to land on the stigma before they lose viability.