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What Are Pollen Spores?

Pollen is an important part of the life cycle of seed plants. Pollen is classified as a type of microspore, meaning it is formed as a result of meiosis, a type of cell reproduction that results in cells containing only half of the full genome, and it produces male gametes, or sperm cells. Pollen itself is not the male gamete, or sperm cell -- rather, it contains structures that create sperm cells, but it also has nonreproductive components.

Structure
- Pollen grains are composed of one or more nonreproductive vegetable cells and a reproductive cell that contains two nuclei. One of the nuclei forms a pollen tube, which is a structure used for transporting the sperm cells into the female part of the plant. The other nucleus splits to form sperm cells. All of these cells, both nonreproductive and reproductive, are encased in a cell wall called an intine. This in turn is surrounded by a protective outer layer called an exine.
Size
- Individual pollen grains can be as large as 100 micrometers, equal to one tenth of a millimeter, or about the thickness of a human hair. The smallest pollen grain, which belongs to the forget-me-not flower, is around 6 micrometers in size.
Production
- The part of the plant that produces pollen is called the microsporangium, which is located in a different structure depending on the type of plant. In flowering plants, the pollen is produced in the anther, which sits at the end of the stamen, also referred to as the male part of a flower. In nonflowering plants, such as conifers, the pollen is produced in the male cone.
Shape and Color
- The pollen grains of different species are incredibly distinctive in shape, as viewed under an electron microscope. Most are round, oval or bean-shaped, and can have either a smooth or spiky surface. Pollen grains are usually white, orange or yellow.

Nature