Lily anther. Light micrograph of a cross-section through a lily bud (Lilium sp.), showing one full anther with four anther sacs (lower centre) and two partial anthers (upper left and upper right). The anther sacs, or pollen sacs, (circular structures with white borders) are filled with developing pollen grains (orange). The pollen grains, or male sex cells, have been produced from the pollen mother cells. The inside of the anther wall produces a nutrient fluid to nourish the pollen mother cells. When the pollen grains are mature, the anther walls split to liberate the pollen grains.