PALYNOLOGY - POLLEN


Pollen grains are an outrageous invention of the seed plants, which first appeared over 300 million years ago. Pollen frees the seed plants from dependence on standing water for fertilization, which is needed by the spore-reproducing plants like ferns. The distinction is similar to the difference between amphibians vs. reptiles. Pollen is produced in the male organs of the flowers - anthers. Pollination occurs when pollen is transfered from the anthers to the female organs by wind (anemophyly) or by animals (zoophyly). If the female stigma is receptive to a pollen grain, the pollen produces a pollen tube, which grows through the female tissue to the egg, where fertilization takes place by the sperm nucleus. Standing water is not necessary. In Angiosperm flowering plants, a second nucleus in the pollen grain unites with two other haploid cells in the ovary, producing triploid endosperm tissue which stores nutrients for the developing seed. For example, the white fluffy part of popcorn is endosperm.
The pollen wall is designed to protect the sperm nucleus from dessication and irradiation during transport from the anther to the stigma, The tiny (20 - 100 µm) pollen grain is coated with waxes and proteins held in place by sculpture elements. The outer pollen wall is made up of a two layers (tectum over a foot layer + intine). These are separated by layer of strengthening rods (columella). This construction prevents the wall from collapsing and crushing the genetic material if the pollen grain looses water. A cellulose wall (intine) lies within the outer pollen wall, which is made of the biopolymer sporopollenin. Escape of the pollen tube through the wall takes places through apertures, which further facilitate shrinking and swelling.



Fossil pollen grains are distinguished primarily by their form and their surface sculpture. The following Key distinuishes 17 basic pollen classes.

A. Pollen in groups of four grains..TETRADS
AA. Pollen in groups of more than four grains..POLYADS
AAA. Pollen grains free
  BB. Aperture one or grain without apertures
    C. With bladders or meridional ridges
        D. With bladders.............................VESICULATE
        DD. With deep meridional ridges..............POLYPLICATE
    CC. Without bladders or meridional ridges
        D. No distinct apertures.....................INAPERTURATE
        DD. One aperture
            E. Aperture elongate.....................MONOCOLPATE
            EE. Aperture +/- circular................MONOPORATE
  BB. More than one aperture
    C. Without lacunae in a fixed geometrical pattern
        D. Apertures not fused
            E. Furrows present, no free pores
              F. Furrows without distinct pores or transverse furrows
                G. Three furrows..................TRICOLPATE
                GG. More than three furrows
                  H. All furrows meridional....STEPHANOCOLPATE
                  HH. Furrows not meridional....PERICOLPATE
              FF. Furrows with distinct pores or transverse
                G. Three furrows..................TRICOLPORATE
            EE. Three pores present, no furrows
              F. Three pores.......................TRIPORATE
              FF. More than three pores
                G. Pores in an equatorial zone....STEPHANOPORATE
                GG. Pores evenly distributed......PERIPORATE
        DD. Apertures fuses to rings etc. ...........SYNCOLPATE
    CC. With lacunae in a fixed geometric pattern
        D. Lacunae elongate (pseudocolpi)............HETEROCOLPATE
        DD. Lacunae not elongate.....................FENESTRATE

Owen Davis 12/99