It is easier to understand the interactions of pollen and stigma surface, if we learn previously a little about the surface properties of both structures. The structures of the pollen grains of different plant species vary mostly in the nature of their walls called sporoderm. Structural details can only be made out in the microscope or the electron microscope. The surface can best be studied with a scanning electron microscope . Pollen that is distributed by the wind has to travel large distances.
Pollen grains are rather small and their surface is smooth.
Only rarely as in the case of Pinus and Picea , for example are they equipped with lateral airsacs. The pollen grains have to stick to each other and to the bodies of the insects. Typical angiosperm pollen is the only proof that this plant group has already existed during the lower Cretaceous and perhaps even in the Jurassic period. Pollen analyses are also well-suited for the elucidation of the late past of floral history. Successions of plants representative of bog formation, for example, can be captured that way.