Pollination is the process through which plants reproduce, by ensuring that male gametes are spread to female gametes, allowing the plant to produce seeds which will in turn develop into new plants. The process of pollination is important to people in a number of fields, including gardeners, farmers, and biologists, all of whom rely on pollination and the resulting fertilization. There are a number of different ways in which pollination can happen, and some plants have evolved very complex techniques for pollination.
The male part of the plant, known as the anther, produces pollen, a sticky material which contains genetic material. Pollination occurs when the pollen comes into contact with the ovule, the female part of the plant. In flowering plants, known as angiosperms, the pollen is transferred to the stigma, which transports the pollen to the ovule. In gymnosperms like conifers, the pollen is applied directly to the ovule.
Many plants are capable of self-pollinating, which involves spreading their own pollen onto their own ovules. However, cross-pollination is preferred, because it increases genetic diversity, making the plant species as a whole stronger and more likely to survive. Plants can accomplish cross-pollination by luring pollinators such as bees and insects onto their anthers, with the pollinators picking up the pollen and dropping it off on other plants. Cross-pollination can also happen when plants release their pollen into the air, relying on the wind to carry it to other plants. Humans are often familiar with this form of pollination, since ambient pollen in the air can trigger allergic reactions.
A variety of techniques can be used by plants to avoid self-pollination, such as features on the flower which prevent contact between the anther and the ovule or stigma. Plants are also capable of recognizing their own pollen, which allows them to trigger a chemical response which prevents fertilization if they become self-pollinated.
Once a plant is pollinated, the ovule becomes fertilized, and it can start to develop into a seed. Many seeds are covered in protective coatings so that they will not be damaged by animals or the elements, and some are encased in fruits which are meant to appeal to insects, birds, and other animals. When animals eat the fruit, they excrete the seeds later in a distant location, spreading the plant in the natural environment. Some plants are so specially developed that their seeds actually need to go through a digestive tract in order to germinate.