"Classification of Pollination"

Pollination is process which transfer of pollen from stamen to the stigma of the flower.There are two types of pollination,self-pollination and cross-pollination.

Self-pollination can make sure that the species of the plant would not go into extinction as two different plants are not needed to produce.If two different s plants of the same species are required then there is less chance of pollination happening that often.In other words less offspring produce in cross pollination so there is other chance of extinction,but plants using self pollination have nothing to fear.They can produce offspring in their own using one parent. The offspring produce are genetically identical to the parent so that means if the parent plant can survive in a certain habitat then the offspring will also surely be able to survive in the same habitat.                              

Cross pollination occurs when the two flowers involved are from different plants rather then from the same one. Two flowers from different plants mean that different set of genes are involved. It also very important to remember that the two different flowers involved must be of the same species.

So you can also define it in another way.Cross-pollination occurs when the anther and the stigma are in  flower of different plant of the same species.

therefore i conclude that pollination is a difficult process, it has several ways to pollinates.