Pollen cell. In flowering plants the vegetative tube cell produces the pollen tube, and the generative cell divides to form the two sperm cells. Pollen is produced in the microsporangia in the male cone of a conifer or other gymnosperm or in the anthers of an angiosperm flower. Pollen grains come in a wide variety of shapes, sizes, and surface markings characteristic of the species (see electron micrograph, right). Pollen grains of pines, firs, and spruces are winged. The smallest pollen grain, that of the forget-me-not ("Myosotis" spp.), is around 6 µm (0.006 mm) in diameter. Wind-borne pollen grains can be
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