Most people love to be given a big bunch of flowers. They are beautiful, they often smell great too, and can be given to say “thank you”, “congratulations” or “I love you”. Flowers are an important part of human culture. As well as giving them as gifts, we use them to decorate weddings and brighten funerals and graves. We collect their scent to make expensive perfumes and use images of them on everything from wallpapers and fabrics to jewellery and pottery. And some flowers are used to make herbs and spices, dyes, drinks, medicines and even illegal drugs.
But why do flowers exist? It is not just because we like to have them around. Flowers are an essential part of most plants. They are a plant’s reproductive organs—the parts it uses to reproduce, or make copies of itself. Flowers do this by making fruits and seeds that can grow into new plants.
GROWING ON PLANTS
Most plants are flowering plants. Their flowers usually grow somewhere near the top of the plant. A flower starts life as a tiny bud that grows from a branch or stem. Most buds are green because they are surrounded by leaf-like coverings called sepals. When the parts of the flower have formed inside the bud, the sepals open out to reveal the petals. Some plants grow just one flower each, while others can have hundreds.
In many plant species, the arrival of spring and summer tells the plant to grow buds and tells the buds when to open out. A plant can sense that the days are becoming longer and that the temperature is getting warmer, so it knows when spring is coming. Plants usually grow their flowers in spring because their seeds will have the best chance to grow while the weather is warm and the soil is soft and damp, instead of dry or frozen.
DO FLOWERS GROW ON THEIR OWN OR TOGETHER?
Flowers can grow singly or they can be composite flowers, which means that the flower head is made up of many smaller flowers, known as florets, growing together in a cluster. Dandelions and daisies are composite flowers. Each petal is really a separate flower with its own carpel and stamens inside.
Grasses are flowering plants, but you do not usually see grass covered in flowers. That is because grasses only grow very small, plain flowers. They do not have large petals or bright colours. Instead, each flower is enclosed by simple, green, leaf-like parts called bracts.
FLOWERS IN CLOSE UP
There are thousands of different types, or species, of flowering plants, and their flowers come in a huge range of shapes, sizes, and colours. However, most flowers have the same basic parts—sepals, petals, carpels, and stamens. These are the parts that allow fruits and seeds to grow and reproduction to take place.
Sepals are leaf-like parts that grow around the outside of a flower. When the flower is a bud, the sepals surround it and protect it. After the flower opens out, you can see the sepals around or under the petals.
Petals give a flower its colour and shape. They are usually soft and delicate, and often brightly coloured. Some flowers, such as buttercups and pansies, have a ring of several petals. In others, such as daffodils and bluebells, the petals are joined together to form a tube, bell or trumpet shape.
Carpels are female parts that grow in the middle of a flower. Some flowers have just one carpel, while others have several. A carpel is made up of a tube-shaped part called the ovary, with a sticky part called the stigma on top. Inside the ovary are many tiny ovules. They are the parts that eventually turn into seeds.
Stamens are the male parts of a flower, and they grow around the carpel. Each stamen is made up of a stalk called a filament and a tip called an anther. The anther contains lots of male cells known as pollen, which looks like a kind of yellow dust.
WHAT IS FERTILIZATION?
In order to make seeds, a flower has to be fertilized. This happens when a grain of pollen (a male cell) joins up with an ovule (a female cell). It is usually better for the carpel of one flower to be fertilized by pollen from a different flower on a different plant of the same species. This is because living things are usually stronger and healthier if they contain a mixture of different genes from two different parents.
When a grain of pollen lands on a flower’s stigma—as long as they are both from the same species—the pollen cell grows a long tube called a pollen tube. The pollen tube reaches down into the ovary, and into an ovule. Each ovule that is fertilized by a grain of pollen then turns into a seed. Finally, the plant releases the seeds so that they can grow into new plants.
WHAT IS POLLINATION?
Pollination means transferring pollen from the male stamens to the female carpels so that fertilization can happen. Many plants have both stamens and carpels within the same flower, and some can fertilize themselves by scattering their pollen on to their own stigma. This is called self-pollination.
Some flowers release their pollen while their carpels are still not fully developed. The flower’s stigma only develops and becomes sticky after its own pollen has been blown or carried away to fertilize other flowers. This means the flower can only be pollinated by a different plant. Some plants, such as maize, have two different types of flowers on the same plant—some male and some female. And a few plants, such as holly trees, can be either male or female. Male holly trees grow male flowers with stamens and pollen, and female holly trees grow female flowers with carpels and ovules—so holly trees cannot pollinate themselves. When a flower is pollinated by pollen from another plant, it is called cross-pollination.
A HELPING HAND
Since plants cannot walk, they need help to carry their pollen from one plant or flower to another. As pollen is so fine and light, it can often float on the wind from one plant to another. But many flowers are pollinated in another way—by insects. When an insect such as a bee or a moth flies into a flower to feed on its nectar and pollen, some of the pollen sticks to its body. When it visits another flower, some pollen may brush off onto that flower’s stigma and fertilize it.
WHY ARE FLOWERS BEAUTIFUL?
The main reason why so many flowers have beautiful petals, strong scents, and sweet nectar is to attract insects. Many insects, especially bees, feed on nectar and pollen from flowers, but this does not harm the flower. By providing these things, flowers make sure insects will visit them and help to spread their pollen around. Bright colours and strong scents help insects to find flowers from a distance and zoom in on them.
Not all flowers smell sweet. Some, called carrion flowers, smell like rotting meat instead. This is because they are pollinated by flies, and flies love the smell of rotting meat. The flies buzz around the flower, and although they may not find anything they want to eat, they still transfer the pollen.
DO ALL PLANTS HAVE FLOWERS?
Most plants are flowering plants, but there are a few types that do not have flowers at all. For example, mosses and ferns reproduce by making tiny seed-like objects called spores and do not need flowers. Conifer trees make their seeds in scaly cones instead of having flowers.
As we use flowers in so many ways, flower farming is an important industry in many countries. In the Netherlands, farmers grow millions of red and yellow tulips in enormous tulip fields. Besides picking and selling the tulips, the farmers also make money from tourists who come to watch them growing. In countries such as Turkey, India, Iran, and Ethiopia, roses are farmed for making perfumes. In some countries, including Afghanistan and Thailand, many farmers make a living growing opium poppies, which are made into the drug heroin.
Did you know?
• The biggest flower in the world is the Titan Arum, which grows up to 1.8 metres tall. It is not a single flower, but a composite made up of many much smaller florets.
• The Rafflesia, or corpse lily, is the world’s biggest single flower. It grows up to 1 metre across.
• It takes over 400 kilograms of rose petals-the same weight as about six adult men-to make one small 100-millilitre bottle of rose attar (perfume oil).
• Bees can tell dozens of different species of orchids apart by their slightly different scents.
• Sunflowers slowly turn around during the day so that they are constantly facing the Sun.
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