Pollen as large as about 90–100 µm. In angiosperms, during flower development the anther is composed of a mass of cells that appear undifferentiated, except for a partially differentiated dermis. As the flower develops, four groups of sporogenous cells form within the anther. The fertile sporogenous cells are surrounded by layers of sterile cells that grow into the wall of the pollen sac. Some of the cells grow into nutritive cells that supply nutrition for the microspores that form by meiotic division from the sporogenous cells. In a process called microsporogenesis, four haploid microspores are produced from each diploid sporogenous cell
Bee pollen in the chambers of honeybee hives, and sometimes in wood and mud created by female ground-nesting bees, such as the leafcutting bee. With the leafcutting bee, when the pollen ball is complete, a single female lays an egg on top of the pollen ball, and seals the brood cell. It differs from field gathered pollen as honey bee secretions induce a fermentation process, where biochemical transformations break down the walls of flower pollen grains and render the nutrients more readily available. Forager bees that gather pollen do not eat it themselves, since they stop producing the proteolytic enzymes necessary to