An Introduction to Flowers
An Easy Guide to Understanding the Science of Flowering Plants
Oct 30, 2008
There is evidence to suggest that the evolution of flowers began 250 million years ago, although solid evidence is only provable from about 130 million years ago; today over 80% of green plants have flowers. The flower is the reproductive part of a flowering plant (also known as an angiosperm) and works in a similar way to that of humans; the object is to create a union between the male and female parts in order to produce the seeds needed for a new plant.
The Parts of a Flower in the Reproduction Process
A normal flower has four parts joined to the end of the stalk, arranged in a symmetrical way; these parts are arranged in four whorls, or circles. The layer of circles is broken down into:
- Calyx - the outer circle of sepals
- Corolla - the inner circle, which usually attracts insects for pollination
- Androecium – from the Greek word andros oikia meaning man's house – contains the stamens
- Gynoecium – from the Greek word gynaikos oikia meaning the woman's house - contains the pistils.
How a Flower Reproduces
Although flowers may differ from species to species, the general process of reproduction in flowers is the same. A flowering plant usually contains both the male (pollen) and female (ovules) spores for reproduction and both male and female organs. The stamens each have a filament, on top of which is the anther, where pollen is produced. The pistil, containing the carpel of an ovary and ovules, has a sticky tip called the stigma, which is the receptor for the pollen.
How a Flower Attracts a Pollinator
Many plants can pollinate their own flowers (such as some species of Salvia and Viola) but some need help from external sources such as the wind and insects; it is not uncommon for bats and birds to help in the pollination of a plant. Flowers have various methods to employ in attracting potential pollinators; vivid colors, aromatic scents and nectar sugar are some attraction methods.
Some species of birds and bees have 'color' vision; nectar patterns, visible under ultra-violet light but readily visible to some bees and insects, attract certain pollinators. Some flowers, such as certain species of orchids, can even imitate female bees in shape, scent and color; male bees move from flower to flower in the search for a potential mate, pollinating as they go.
The Pollination of Flowers by Insects: Entomphilous
In the process of landing on a flower, feeding on the nectar and moving onto the next flower, an insect or animal collects pollen on their body and rubs it off on the next flower. Flowers are arranged so that the stamens allow for pollen to be collected and the stigmas are positioned to receive the pollen.
Many flowers attract one particular species of insect and it is said that their relationship is one of co-evolution, which has developed over a long period of time. Some plant species become endangered when their pollinator population shrinks, resulting in a possible extinction of both plant and insect species.
The Pollination of Flowers by Wind: Anemophilous
Flowering plants which exist in wet, windy and cold climates rely on wind for pollination; examples of this type of pollination are grasses, maples, ragweed and birch trees. They do not have a need for colorful flowers or sweet smelling, nutritious pollen, although some bees do collect corn pollen. Pollination by wind is more haphazard than insect pollination and therefore trees and grasses grow in groups to increase their chances of pollination.
The Formation of a Seed
When pollen is successfully transferred to the stigma of a flower, it results in the growth of a pollen tube which eventually travels down into the ovary; the pollen tube allows a male sex cell to fuse with a female sex cell in the ovary, producing a seed. The ovary grows into a fruit, protecting the seeds; the seeds are released when ripe and spread by animals, water or the wind.
References:
Taylor, Barbara 1997 Inside Guides: Incredible Plants UK: Dorling Kindersley Ltd
For Further Reading:
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