The process by which pollen is formed is called microsporogenesis. The swollen part of the stamen head of a flower is called the anther. Anthers contain one or more archisporial cells. Each archisporial cell is large in size, the cytoplasm is dense and the nucleus is large. It produces two cells by periclinally dividing. wall cells on the outside and primary reproductive cells or sporogenous cells on the inside. Wall cells divide to form the pollen wall. The outermost layer of the wall is called the tapetum. Sporogenous cells transform into pollen mother cells either directly or by division. Each pollen mother cell divides by meiosis to form four microspores or pollen grains. The four pollen grains together are called tetrads. Most of the pollen is yellow in color. The pollinator receives nutrients from the tapetum. Plants belonging to the family Orchidaceae, Asclepiadaceae etc. have pollen grains together. Pollen sticks together in the metamorphosis to form a special structure. This is called a polynomial.
[Anthers with four anthers are dithetic anthers and this condition is called tetrasporangiate. An anther having two anthers is monothecus anther and this condition is called bisporangiate.