Egg cell production in plants requires fertilization process,during which pollens, as the male reproductive cells,meet and unite with ovule as female reproductive cells this process takes place in the flower ( the reproductive organ in plants ).
A perfect flower has both stamens ) pollen producing organ ( and carpels ) egg producing organ (. During the first phase in the fertilization of an egg,pollination,pollen is transmited onto the stigma of a carpel. This transfer is carried out in four ways : 1- Insects,most plants depend on the activity of such insects as honey bee for their fertilization.While making use of nectar and pollens of flowers as food,sticky pollens adher to their body parts.When flying from flower to flower they transfer these pollen grains to the stigma of the flowers visited; apple,pear,almond and peach trees are among plants which depend on insects for their fertilization.
2- Weight,in some plants stamens are located on carpels in a way that their pollen grains, as a result of their weight,fall onto the stigma hence,pollination takes place.
3- Human pollination,in some plants like date palm in which the flowers are not completed in themselves that is,their male and female sexual organs are located on two different trees,for higher yield,pollination is carried out by human. In this method pollen bearing flowers of the male tree are cut and shaken over the flowers of the female tree . This method is also done for other plants such as Lebnaneese red apple ) red delicious ( when economical.
4 - Wind,in some kinds of plants pollination is carried out by wind ;the pollen grains of these plants are readily distributed by wind because they are light and dry and have a special shape.Flowers of such plants do not generally have scents,nor do they have very attractive colors,their stigmas are usually big and leaf-like so that they can receive a great number of pollen grains . Pollen production in these kinds of flowers is extremely high , so that all flowers would certainly receive pollens.For example,walnut, hazelnut and pistachio trees and among crops oat,and corn,belong to this group.It is worth saying that plants which need wind and insects for their pollination are generally cross polination.
Of course wind is not always useful for pollination especially for insect-pollinated ones.Because insects,mainly bees,decrease their activity in wind,and strong winds also cause mechanical harms to flowers,make their stigmas dry and create a condition which is not suitable for receiving pollens.