Pollination: Flowers, Bees, and Seeds
Pollination: Worker Bee
Introduction to Pollination
What is pollination? How does pollination occur? Does pollen serve a useful purpose or does it just make people sneeze? What is the difference between self-pollination and cross-pollination? What are pollinators? These are some of the many questions gardeners, kids and others have about pollination.
Pollination plays a major role in our lives whether we realize it or not. Much of the food we consume relies on pollination, so pollination is important for all of us. Pollination is critical for any garden. If there were no pollinators, most flowering plants could not reproduce. Different plants different kinds of pollination.This article explores the various ways plants pollinate.
Approximately ninety percent of plants are flowering plants. Flowers are the easiest place to begin understanding the pollination process. So we will explore the reproductive parts of flowers before discussing the various types of pollination.
Parts of the Flower
Hibiscus male stamen (yellow) and female pistil (red). The (yellow) stamen consists of filiment (stalks) and the anthers (yellow tips). The (red) pistil consists of the stigma (tips) and the style (tubes) that run down into the ovary.
A rose pistil with the stigma that captures the pollen not shown, the pollen then travels down the pollen tubes of the style (stalks) to the ovary (ovule, white).
Flowers are a big part of our lives. We use flowers to help us mark many of the most important events in our lives. As often as we admire, enjoy, send or receive flowers, they have us distracted by their beauty and scent. However, flowers do much more than just look beautiful and smell good.
Flowers are the reproductive part of the plant. When a plant flowers, it is trying to attract attention from pollinators. The flower blooms in brilliant, vibrant colors, often provides nectar and/or omits strong scents to attract pollinators in order to reproduce. All flowers, great and small, exist to make new plants.
The scent, appearance and even the opening and closing of a flower all serve the reproduction process. Flowers bear the male and female cells needed to produce seeds.
The pistil and stamen are two important reproductive parts of the flower (see photo, above). The pistil or female part of the plant, is in the middle of the flower. The pistil is where the egg cells are kept, it also contains the stigma, the style and the ovary.
The ovary is the part of the plant that becomes fruit, while the ovules become seeds.The stamen are the skinny stalks around the pistil. The stamen are the male part of the plant where pollen is produced. The stamen is made up of the anther at the top and the filament. The filament are the thin stalks supporting the anthers. The anthers release pollen.
Not all flowers contain both the pistil and stamen, but the ones that do are called perfect flowers. The lily, rose and sweet pea are examples of perfect flowers. Flowers that have only the pistil or the stamen are called imperfect flowers. However, the same plant can have both male flowers and female flowers.
- Many of us are familiar with pollen as an allergen. While it causes allergies in many, pollen is crucial for plant reproduction. Pollen grains are produced in the male organ or stamen of flowering and cone-bearing plants. It contains the male sperm.
- Reproduction is the purpose of pollen. The pollen must travel from the anther of the stamen to the pistil's stigma. There is often a sticky liquid on the stigma to facilitate this process. The sperm cells in the pollen then travel down from the stigma down a tube that forms from the style to the ovary.
- Pollen grains vary in size, shape and features of the outer shell, but every pollen cone has a protective outer shell. This is to protect the cells during pollination and prevent them from drying out. When the pollen tube enters an ovule it releases two nuclei. One is joined with the egg cell in the ovule to develop into an embryo of a new plant. The other develops into nutritional tissue as a food source for the new embryo or seed. This is fertilization.
Pollen is produced in the male organs of the plant and transferred to the female organs. This transfer of pollen is pollination. The result of pollination is fertilization, seeds and new plants. Pollination is the how plants reproduce. Most specifically, the transfer of pollen from the anther of the stamen to the pistil's stigma is called pollination.
Pollination results in the development of a seed. In cone-bearing plants, the pollen is produced in the male pollen cones and transferred to the female pollen cones during pollination. This is a closer look at the different ways this transfer, pollination, is accomplished by different plants.
What Are Pollinators?
Pollinators are insects and animals that often unknowingly transfer the pollen from one flower or plant to the pistil of another flower or plant. Honeybees are by far the most important pollinators. Honeybees live entirely on pollen and nectar and the worker bee's body is amazingly designed to accomplish the task.
Butterflies may not be as effective as bees, but butterflies are still good pollinators. Butterflies live entirely on the diet provided by flowers. Butterflies visit flowers for the nectar to feed themselves by using their long tongues. They do not gather food for their young, but lay their eggs on plant stems and leaves. The resulting caterpillars then eat those leaves. Butterflies are active during the daytime and have keen eyesight. Butterflies respond to the flower colors and shapes rather than scent. Their favorite blossoms have throats too deep for many other insects.
Other pollinators include flies, beetles, ants, birds and bats. There are many species of flies, but only a few are connected to flowers. These flies also visit flowers only to feed themselves. Beetles pollinate only a few plants, many of which have trap flowers. Once inside, these flowers trap insects as a way of promoting pollination.
Ants love pollen and nectar, but they are not generally considered good pollinators. However, there are a few species of plants that are regularly pollinated by ants. Birds do a great deal of pollinating in many parts of the world. Their feathered bodies easily pick up pollen. Nectar is a high-energy food enjoyed by birds.
However, birds also do not feed nectar to their young and they rarely eat pollen. Birds and their chicks feed on insects sometimes captured in flowers. In the United States the beloved hummingbirds are the only ones that visit flowers. Bats, which are considered the only flying mammals and are not considered birds, are also pollinators, as we will see.
Pollination does not stop when the sun goes down. Moths take over for butterflies and bats take over for birds. You may have noticed flowers that bloom at night are so often in brilliant, pure whites.
Most moths fly at night, pollinating night blooming flowers, light in color and exceptionally strong in fragrance. Moths do not perch, but hover over flowers, drinking the nectar by putting their tongues down the throat of the flower. Moths differ from butterflies more in habit than body structure.
Both moths and butterflies pollinate some of the world's most exotic flowers. Most bats eat insects and a few bats eat fruit, but many of them also love nectar.Bats fly at break neck speed, stopping briefly to hover over a flower to extract the nectar. Like some of the insects we have seen, the furry body of the bat inadvertently picks up and carries pollen to the next flower. In some tropical areas, many plants depend entirely on bats for pollination. Bats help pollinates some of our most popular fruits, such as bananas, avocados and mangoes.Short leaf pine female cone showing seeds.Short leaf pine female cone showing seeds.
Female Conifer Cone
What is a conifer? The name conifer literally means cone-bearer, but this characteristic is not unique to conifers. Thus, not all conifers are so easily recognizable as are junipers, spruces and pines. It is the structure of the seed cones that is unique to conifers. All conifers bear cones or cone shaped fruit that begin as a tight cluster of female flowers. The cones develop to provide nourishment to the growing seeds after fertilization. A mature female cone is the fruit of the conifer and is a woody structure.
Male flowers may also grow in the shape of cones, but botanically they remain fruit even if some may refer to them as cones. Most conifers carry both the male and female flowers on the same tree. However, some are born on different plants. When the pollen ripens on the male flower it bursts, often over a wide radius. The pollen is then caught and retained by the female cones.
Fertilization then takes place and produces seeds after ripening in the protection of the female cone. Once the seeds have matured, the female cone opens up releasing the seeds. The seeds then drop from the tree to be dispersed by birds or the wind.
Most conifers and about twelve percent of flowering plants rely on the wind for pollination. A few, such as the willow and maple, use both insect pollination and wind pollination. Their flowers have nectar to attract insects, but they also release their pollen to the wind.
Wind pollinating plants are quite different than insect pollinating plants. Ragweed and other plants that rely on the wind for pollination do not need showy flowers, strong scents or nectar in order to attract pollinators. Wind pollinators that do have flowers, generally have small dull ones that are green or yellowish in color. This includes many grasses and trees.
A plant or tree that relies on the wind for pollination releases millions or even billions of pollen grains. Their pollen is light weight and easily takes flight. Ragweed is one such plant and many are allergic to the pollen. When the ragweed pollen count is high it is because the plants have released their pollen in hopes of achieving pollination.
Wind pollinators play the numbers game. By releasing millions or billions of pollen grains into the air the chances of it hitting its target greatly increase. The stigma (top of the pistil of the female part of the plant) of wind pollinators is usually large and prominent, exposed to the wind and designed to capture the airborne pollen with a feathery surface.
Nearly every plant in the world is pollinated by insects, animals or the wind, but like most rules there are exceptions. In this case the exceptions are few. It seems counter intuitive for a plant to water pollinate. Water is generally an enemy of pollen. Also, most water plants are pollinated above the surface of the water because they are exposed to the air, wind and insects in order to pollinate. They pollinate on the water in spike of the water. However, the familiar aquarium plant, vallisneria, uses the water for pollination.
The female flowers of the vallisneria grow on long stems reaching the surface of the water.The vallisneria is not seeking the wind or insects to pollinate. Instead, the male flowers grow in clusters with short stems that break off and float to the surface of the water. On the surface of the water the male holds up the stamens until they bump against a female causing their pollen to scatter on it. After pollination, the female flower stem coils up and pulls the female back down under the water where it forms its seeds close to the bottom of the aquarium or pond.
Cross-pollination is the most common method of pollination. Cross-pollination is the transfer of pollen from the stamen of one flower to the pistil of another plant. In order for seeds to develop in nature, the cross-pollination must occur between the same or closely related species. However, botanists have artificially cross-pollinated to create new varieties of corn, cotton, wheat and other plants.They use special brushes to transfer the pollen from one plant to another.
Self-pollination occurs when the pollen of one plant is transferred from the stamen of that flower to the pistil of the same flower, or to another flower on the same plant. Beans, cotton, peas and wheat normally self-pollinate.Certain cross-pollinating plants are also able to self-pollinate, such as pansies.
Some flowers are unable to self-pollinate by their own structure or development. For example, the stamen ripen earlier than the pistil, so the pollen is disbursed before the pistil of the same plant is ripe. Then there are imperfect flowers, such as on the willow tree. In this case, each plant bears either the male stamen or the female pistils, but not both.
Pollination of the Titan Arum
Lest we believe all flowers attract pollinators with lovely scents, there is the Titan Arum. The rare and truly unusual Titan Arum, also known as the Corpse Plant, does not attract pollinators with lovely scents. When the female receptors are ready for pollen, they omit an odor of, you guessed it, a rotting animal.
The rotten odor attracts dung beetles and flies to achieve pollination. For more on this striking plant and what is perhaps the stinkiest pollination on earth, see the video. The Titan Arum can grow to nine feet (2.7 meters) tall.
Pollination is vitally important for plants. There are a variety of ways in which flowers, trees and other plants accomplish pollination. Pollinators, the wind and the water can all facilitate the reproductive process of various plants and trees. Some pollinators work during the day, while others pollinate at night.
The following reference material was consulting during the creation of Pollination: Flowers, Bees and Seeds.
- Conifers of the World: The Complete Reference, by James E. Eckenwalder. Experiment Central, 2nd edition, Flowers, pp. 432-7, available online through the local library's online reference material.
- Gardening with Conifers by Adrian Bloom. Insects and Flowers: A Biological Partnership by John Brackenbury.
- Plant Life for Children : All About Plant Pollination : Fruit, Flowers and Seeds, DVD.
- The United States Forest Service, Celebrating Wildflowers, Wind and Water Pollination, online at fs.fed.us.
- What Is Pollination? (Big Science Ideas), School Education Video, by Make Me Genius [dot] gov, video immediately above.
- World Book Encyclopedia, 2009 edition, Pollen, Pollen Grains, Methods of Pollination and Fertilization, pp. 644-5.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
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© 2019 Kelly Ann