Pollination is the act of pollen being moved from the anther of one flower to the stigma of another flower of the same species. That is the simple explanation of it, but I will go into a bit more detail below.
The goal of pollination is for the plant to reproduce by creating a new seed. Then hopefully, but not always, that seed will grow into a new plant. Remember that one of the goals of all forms of life is to survive by reproducing.
What is Pollination?
First, it is important to remember the basic parts of a flower. The male part of a flower, which contains the pollen, is called the anther. The female part of a flower, which will catch and hold the pollen, is called the stigma.
As I stated earlier, all that needs to happen is for the pollen to move from the anther to the stigma. Once the pollen is moved from the anther and manages to land on the stigma then the pollen will grow a long pollen tube. The pollen tube goes down inside of the style till it gets to the ovary. Once in the ovary it will fertilize the flower. If this is successful then a seed and fruit may begin to grow.
Pollination will not work if the pollen of a Lupine flower is moved to a different kind of flower such as a Columbine or Aster. In order for a plant to successfully achieve pollination the pollen must land on the same kind of flower as it came from. Even then, there is a chance that for some reason the flower will be unable to make a seed.
How Can Plants Be Pollinated?
Flowers can be pollinated by animals, wind, or water.
A common example that most people have heard of is a bee that flies to one flower to gather nectar. While it does this some pollen from that flower gets onto its body. Then it flies to another flower to gather more nectar. Some of the pollen on its body may come off and stick onto the stigma of that flower, pollinating it.
Most of the time with animals the flower is pollinated by accident. The animal may be gathering or eating pollen or sipping nectar and while it does this the pollen attaches to it. Then it is spread to another flower in the same way as the animal moves on to another flower. Basically, the flower is attracting the animal with its bright flowers and tasty nectar just so that the animal will spread its pollen.
However, some plants, such as grasses, are pollinated by wind. For grasses the anther and stigma are located outside of the petals so that when the time is right the wind can blow them. Then, hopefully they will land on the stigma of the same kind of grass, successfully pollinating it.
What is Cross Pollination?
This is when the pollen of a flower spreads to the stigma of a different flower of the same species. A benefit of cross pollination is to increase the genetic diversity of a plant, which will help it survive disease and drought.
Most wild plants, about 80%, are cross pollinated.
What is Self Pollination?
This is when the pollen of a flower spreads to the stigma of the same flower.
In contrast to wild plants, many domestic plants such as lettuce, beans, and tomatoes are self pollinated.
Can Plants Be Cross or Self Pollinators or Both?
In general plants try to be cross pollinators because that will give them a greater chance at survival. In order to do this plants have different strategies, such as having only male or female flowers. Another strategy used by Avocados is to have the male flowers open in the morning and female flowers to open in the afternoon.
Many plants that are mainly cross pollinators can also self pollinate if they are unsuccessful at cross pollinating. Likewise some self pollinators can cross pollinate if they need to.