Pollination

Since pollen itself is immobile, help is required in order to transport pollen from the loculi of the anthers to the recipient stigma in the pistil so that eventually fertilization can be achieved. This transfer is called pollination. There are in principle three ways to transfer pollen:

Movies on pollen dispersal
Methods of pollination Videomovie by Brittanica.com (article)	Lecture on pollen dispersal: Scientific talk by Dr. Dehgan, Professor at the University of Florida (Link)

 

Disperal by animals: Zoophily

In 80%of the plant families pollen is dispersed by animals, mostly by insects (in this case a process called entomophily from the Greek: insects-friendly), who collect pollen and sometimes also consume it, like bumblebees and bees, but also butterflies and hoverflies. In the tropics also birds, in particular colibries, and mammals like bats are involved in the dispersal of pollen. Plant which depend on animals for pollen transport have nearly always large and colorful flowers with a strong smell to attrack the pollinator. These plant species produce much honey and are often adapted to the visit of one particular type of insect. The pollen grains of such plants have often a coarse surface and they are often covered by a sticky oily fluid, the pollenkitt (more hereabout in "Pollen development").
 

Spreading of pollen by animals
Click on the images for zoom views A: Hoverfly (Eristalis nemorum) on Devil's-bit Scabious (Succisa pratensis) B: Small Copper (Lycaena phlaeas) on Hawksbeard (Crepis sp.) C: Bubble bee (Bombus sp.) D: SEM image of English Daisy pollen (Bellis perennis) E: SEM pollen of Lily (Lilium sp.) Photographs: Marijn Nijssen and Jan Derksen

 

Dispersal by the wind: Anemophily

By dispersal through the air pollen is blown aways from the anthers and reaches the stigma of another plant of the same species by chance. These plants have often small, inconspicious flowers that are clustered in large groups, like in inflorescences of grasses (ears) and in catlins of many trees like Hazel. Characteristic for the anthers of many of those plants is that they stand out. Also the stigmata protrude outside the flowers and they are strongly branched in order to catch as much pollen as possible. Plants employing animophily produce large amounts of pollen grains that are commonly very small, without large extensions or any oily film on their surface. However, some species like Pine (Pinus sylvestris) appear to have large pollen grains, but those are relatively light thanks to their air bags, so that the wind can still carry them.
 

Flowers and pollen of plants with anemophily
Click on the images for zoom views A: Habitus of a flowering grass with stigmata B: Extending anthers in Cockfoot (Dactylis glomerata) C: Close-up of extending stigmain a grass D: SEM view of Common Velvergrass pollen (Holcus lamatus) E: SEM view of Pine pollen (Pinus sylvestris) Photographs: Marijn Nijssen and Jan Derksen

 
Pollen that is dispersed by the wind can reach the mucosa of nose and eyes. Some species can then cause allergy. However, not all types of airborne pollen are as strongly allergenic. Some species that produce a lot of wind-dispersed pollen grains, like the Ash (Fraxinus excelsior, "pollennieuws" video and illustrated descriptions, both in Dutch), do not cause hay fever.

Pollination by water: Hydrophily

Ephydrophilous (i.e. water surface-pollinated) pollen grains are spherical or reniform and large, while hydrophilous (i.e. subaquatic-pollinated) pollen grains are filiform.
 

Underwater pollination
	A and B eelgrass (Zostera). A. Reproductive shoots and B detail of pollen dispersal by water Photograph: Dr. J. Ackerman, University of Guelph, Canada

 
Webpages and photographs:Jan Derksen, Marijn Nijssen, Josef Ackerman and Elisabeth Pierson
Drawings: Lidwien van der Horst
Web development: Remco Aalbers