How seeds sprout
Imagine you are a tiny plant inside a seed. If you are a bean or a pea plant you will look like a walking stick. Your shoot forms the handle and your root forms the long straight length of the stick. On either side you have a suitcase of food. Compared to you, the suitcases are huge and they squash in on you from each side. There is hardly any water in the seed and you are only just alive. You are resting, like a hedgehog hibernating through the winter.

Around the outside of the seed is a tough coat. As you lie in the soil, a passing beetle nibbles at your seed coat. Its jaws are too small to cope and it wanders away to find something else to eat.

You are not cut off completely from the outside world. There is a tiny hole in the seed coat. It formed ages ago and marks the spot where pollen entered to begin your life. Oxygen can pass through this hole so that you can stay alive. Most people do not think that plants need oxygen because they cannot see them breathing. Plants take in oxygen by a process called diffusion. They use it just in the same way as animals - to release energy from food.

When the soil around you becomes warm and wet, water passes in through the hole. It makes the food stores swell up and fills out the wrinkles in your seed coat. Food now dissolves in the water and passes into your body. You use oxygen to release energy from the food and you use the materials that the food contains to grow your root.

As the root grows, the seed coat splits to let it out. The root has a cap of cork on its end. This protects it as it pushes its way through the sharp soil particles. As the root grows down, it also grows fine hairs just behind its tip. They push out between the particles of soil and take in water. In the centre of the root are pipes. They carry the water back into the seed where it can be used to bring you more food.

Once your root is growing well, you use the food to make the shoot. This slowly grows out of the seed coat and moves in the opposite direction to the root. It heads for sunlight and when it reaches the surface of the soil it spreads out two leaves.

By now you have used up almost all the food in your seed so it is vital that you get some more. The leaves provide you with more food. They contain a green substance that traps some of the sunlight falling on them. The leaves also take in carbon dioxide.

There are pipes in the shoot, which connect to those in the root. This means that water can travel straight from the soil to the leaves. When the water reaches the leaves, the energy in sunlight makes the water take part in a change with carbon dioxide. Food is formed in this change which you can use. Oxygen is also formed but there is more than you need and you let it escape from your leaves.

In a short time, you have changed from a living thing that was barely alive to one that is making food and growing so that you can complete your life cycle.

Why has it to be so dry inside a seed?
The seed has to survive in winter conditions. During the winter, water often freezes. When water freezes it expands. If the seed took in water and the water froze, the seed would be damaged. The expanding water would tear up the food stores and the tiny plant. It would crack open the seed coat so that it could no longer offer protection. When the ice melted the seed would just be a soggy mess.

There is a second reason why the seed is kept dry. There are moulds in the soil. They break down the dead bodies of plants and animals. They need water to help them do this. If the seed contained water the mould could enter the seed through the tiny hole and break down the food store and the tiny plant too.

What happens if a seed is planted upside down?
The seed still sprouts and the root still grows down. The shoot also still grows up. Inside the tips of the root and shoot are chemicals that make them grow in the right direction. On a seed packet it may tell you which way up to plant a seed but in the wild seeds land in any position. It is vital their roots and shoots grow in the right direction so the plant has a way of making sure that they do.

Does the food store always stay in the seed?
No. In some seeds the food stores come above the ground and form the first leaves to make food with sunlight. The sunflower is an example of a seed which has its food stores above the ground.

Why don't seeds grow straight away after they have been sown?
Some weed seeds such as shepherd's purse only remain dormant for a short time and the plant can have many life cycles in a year. Most seeds have a period of dormancy. They have this because they grow in places where there are times when conditions for plant growth are not favourable. For example, in Britain the winters can be cold with strong winds. Seedlings cannot survive in these conditions. In deserts there are long periods of dry weather and only short periods of rain when the ground is wet enough for plants to grow.

How long can seeds stay dormant?
The power of a seed to germinate fades with time. Some seeds will fail to germinate after a few days but most can survive from three to fifteen years if they are kept dry and cool. Some seeds have germinated after a hundred years or more.