Plants around the world
Have you blown a dandelion clock to tell the time? The dandelion clock is really a group of fruits with parachutes and when you blow them to tell the time you just count the number of blows it takes to set the parachutes free. At the lower end of each parachute is a tiny seed. When you blow, you send the seed and its parachute high into the air. The fibres of the parachute push against the air as the parachute falls and slow it down. This gives the seed and its parachute a chance to be blown further away by the wind. Imagine that four dandelion seeds rose so high in the air that they were blown to different places in the world. Would they all survive?

The first seed was blown north towards the Arctic. As it came nearer to its destination snowy wastes could be seen below. If the seed landed there it would have no chance. The only plants that survive there are tiny pink plants called algae that live between the flakes of snow. They use water from the snow and minerals from the dust that the wind blows in from other places around the world.

The first seed moved on until a dull brown piece of land came into view. Here, the wind dropped and the seed fell to the ground. It landed close to a willow tree. This tree had branches, which looked like ropes stretched across the ground. They did not rise more than a few centimetres above the soil. There were water and minerals in the soil but the air was cool. The low Sun cast beams on the ground around the seed and warmed it. Over a few days the seed received just enough heat to sprout but when its root grew down into the cold soil there was just not enough warmth to keep it growing and the plant died.

The second seed had drifted south over a desert. It skimmed along over the rocks before it settled on the sandy soil. A stout, green, spiky cactus stood close by. It had roots, which travelled deep into the sand to search for water. The dandelion seed had landed on soil warm enough to make it sprout but there was no water around it. At night the air cooled and dew settled on the seed but by the following day it was so hot again that the seed had dried again. The seed never sprouted and was eaten by a passing insect.

The third seed had drifted over the ocean for thousands of kilometres. If it had landed on the water surface it could not have survived. The ocean contains salt water, which kills most land plants. The only plants that live in the sea are the algae. Microscopic ones live out on the ocean surface while seaweed clothes the rocky shores. The third seed survived its ocean crossing and was blown over a thick green rainforest. A heavy shower of rain washed the seed out of the sky and splashed it onto the top-most leaves of a rainforest tree. The surface of the leaf was waxy and the water, carrying the leaf, flowed quickly across it. The water gathered at the pointed end of the leaf called the drip tip and splashed away through the foliage towards the forest floor. As the seed fell the air became warmer and darker. The seed passed plants perched on tree branches. Many of them had leaves spread out like a winner's rosette and in their centres were pools of water. These plants had made their own water tanks to supply their needs. Eventually the seed reached the floor. It was warm and moist enough for the seed to sprout and soon the root was growing through the soil. When the shoot emerged to try and make food there was simply not enough light so the plant died.

About a kilometre from where you blew your dandelion clock a fourth seed hit the soil. Here there was water, nourishment, warmth and light. In a few days the seed had sprouted and the plant was growing. In a year or two it would produce its own dandelion clocks for someone to blow.

Why do willow trees keep to the ground in the Arctic?
They do this to avoid the strong winds. If they grew like willow trees in Britain, their trunks and branches would be blown to pieces by the wind. All plants that live in the Arctic grow close to the ground to avoid the strong wind.

In the land below the Arctic there are forests of conifers but not forests of other trees. Why is this?
There are two kinds of trees. They are conifers and broad-leaved trees. In the region below the Arctic there are high winds and snowy weather. There is little water in the ground in cold weather. Conifers have straight stems, which are springy and bend with the wind. They have small waxy leaves, which lose only a little water and let snow slide off them easily. These features allow the conifers to survive there. Broad-leaved trees have branching, rigid trunks. They do not bend with the wind but break in the wind. The leaves are large and lose large amounts of water. The tree could not take in enough water from the cold ground to replace the water lost by the broad leaves. Snow could settle on broad leaves and block sunlight until leaves are unable to make food. The snow could also tear the leaves. These features of a broad-leaved tree stop it from growing in the land just below the Arctic.

Why can you find conifers growing on mountainsides?
The conditions on the mountainsides are similar to those in the lands just below the Arctic. Broad-leaved trees can only grow in the valleys below the mountains where the weather is not as harsh. On the mountaintops can be found plants which grow in the Arctic. They grow there because the conditions on a mountaintop are similar to those in the Arctic.

Cacti are large desert plants. Are there any small desert plants?
Yes. Some plants store water, like cacti, and live throughout the year in the desert. They are called living stones because they look like pebbles. Some plants only grow in the desert after a period of rain. These plants spend the dry periods as seeds but after the rains, the seeds sprout and the seedlings grow quickly. Soon the plants become adults, produce flowers and set seeds. By the time they have made their seeds all the water is gone and the plants die. The next generation survives as seeds until it rains again.

Why is it dark in a rainforest?
The tops of the trees have crowns, which grow close together. They form a layer of leaves high above the forest floor. This layer is known as the canopy. Many smaller plants live up there too. They grow on the branches of the trees. The many leaves in the canopy stop light reaching down to the forest floor. This means that it is dark and gloomy in many parts of the rainforest.

How do plants survive when their seeds fall to the forest floor?
The seedlings grow very quickly to find light. They may use the trunks of trees for support rather than waste energy and materials on building a strong stem themselves. As a plant moves towards the canopy it moves into more and more light and so can make more and more food.

Why do plants die if they are planted in the wrong part of the world?
They die because they have bodies which only work in certain conditions. Each kind of plant needs a certain amount of warmth, water, light and nourishment. If the surroundings provide all its needs the plant will grow healthily. If some of the needs are met the plant may survive for some time but if none of the needs is met the plant will die quickly.