<P> Pollen in plants is used for transferring haploid male genetic material from the anther of a single flower to the stigma of another in cross-pollination . In a case of self - pollination, this process takes place from the anther of a flower to the stigma of the same flower . </P> <P> Pollen itself is not the male gamete . Each pollen grain contains vegetative (non-reproductive) cells (only a single cell in most flowering plants but several in other seed plants) and a generative (reproductive) cell . In flowering plants the vegetative tube cell produces the pollen tube, and the generative cell divides to form the two sperm cells . </P> <P> 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 as large as about 90--100 μm . </P> <P> 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 . </P>

Where are pollen grains produced in a flower