Why Plants Have Flowers

Flowers are a way some plants reproduce, making new, young plants that are a little bit different from the parent plants. If every plant was the same and conditions changed - a new disease showed up or the climate got colder - the species might disappear. By constantly making new mixes of the parent plants' different properties, a species is more likely to have some individuals that can survive.

How does this work? Cells, called pollen, from one flower have to get to another flower. The flower that gets the pollen can ripen into a fruit with seeds. The seeds then can grow into plants which have a mixture of the properties of both the plant that made the pollen and the plant that got the pollen.

How Does Pollen Move?

There are several different ways for the pollen to move from one flower to another. The most common pollen movers in New York State are wind and insects. Wind pollinated flowers are usually not very showy to look at, but make huge amounts of pollen. That way at least a little of it might be blown to another flower of the same kind of plant. Grasses and ragweeds use the wind to move their pollen, giving some people hay fever when they are in flower.

Insect pollinated flowers have to advertise so that insects will find them. They also have to bribe the insect with some food so the insect will want to visit several flowers. Insects may eat some of the pollen. Many plants also have some sugar water called nectar in their flowers which insects can eat. Most plants that have pretty flowers are advertising for pollinators.

Flower Parts:

The parts of a flower are arranged like circles, inside each other. Some flowers have 4 different kinds of circles. For drawings of flowers with parts labeled, visit Mendel Web. Our own Fast Plant Flower Close-ups page (see left navigation) has photographs.

In many flowers, the outside circle is made of green, leaf-like parts. These are called sepals and they probably protect the flower some when it is in the bud.

The next circle is the petals. Showy insect pollinated flowers have bright colored petals which help get the attention of pollinators. They may have markings which show insects where the nectar is or may be shaped in a way that sends the insect past the pollen.

If a flower makes pollen, its next circle is the stamens which make pollen and hold it where insects or wind can move it. The knob at the top of the stamen which has pollen in it is called the anther and the stem which holds the anther up is called the filament.

If a flower receives pollen, it has a pistil at its center. The pistil has a sticky surface at the top for the pollen to land on and begin to grow. This sticky or hairy top is called the stigma. It is at the top of a stem called the style. At the bottom of the style is a swelling which has the future seeds in it. This swelling is called the ovary.

How It Works:

When wind or an animal moves grains of pollen to a flower's stigma, they stick there. Each grain of pollen grows a tube down the style to try to fertilize a part inside the ovary. Then these parts, called ovules, can develop into seeds. If you have ever seen the silk on an ear of corn, you have seen very long pollen tubes which grew down into the corn flowers to pollinate each of the kernels on the ear of corn.

Why Do Plants Have Flowers?

Flowers are one way some plants reproduce. They help a plant population in an area mix its properties enough to be ready to survive changes in the environment.

For More Information:

Partners in Pollination is a Web site with lessons on pollination.

See also the ESP Flowers page.