Without plants, there would be no life on Earth - no oxygen for us to breathe, and no food to eat. Plants flourish wherever there is sufficient warmth, moisture and light. They give us food, shelter, medicines, fuel, clothing and raw materials - 25 per cent of manufactured goods are in some way derived from plants. And they add beauty to our lives.

A great diversity of plant life has adapted to the enormous range of environments on Earth. And flowering plants have developed a hugely successful method of reproduction, enabling them to survive and to colonise new areas.

Seeds contain the genetic information to reproduce the parent plant. They have wonderful powers of survival. They can stay in a dormant state for great periods of time - some for hundreds of years - then, when conditions are right, burst into life, maybe thousands of miles from the parent plant.

But many plant species around the world are threatened with extinction, because of changes in climate or land use. As many as a quarter of the world’s flowering plants could be lost in the next 100 years. While it would be best to conserve threatened species by protecting their habitats, this is not always possible. So scientists are looking at ways to conserve the plants themselves.

Seed banking is a relatively new technique whereby seeds are collected and safely stored in the correct conditions. This helps to maintain the diversity of species that are available for the future. Seed banks offers an insurance service in case of the failure of other conservation techniques.

The Millennium Seed Bank project at Wakehurst Place in West Sussex aims to preserve flowering plants from extinction by safe-housing their seeds. Seeds from endangered habitats could be stored for centuries if necessary, and used in the future for purposes such as halting the spread of deserts, or for medical research.

This seed bank, established by the Royal Botanic Gardens, Kew, is one of the largest international conservation projects ever undertaken. By 2010, the purpose-built Wellcome Trust Millennium Building is expected to house seeds from around 10 per cent of the world’s seed-bearing plants, especially those from more arid regions.

The seeds are carefully selected, dried and stored. Most seeds, whatever their size, have a long life span. If carefully dried and kept at a temperature of 20 degrees below zero, they can be expected to live for centuries - Arctic lupin plants grew from 10,000-year-old seeds that had been found frozen in the Canadian Yukon.

Nearly all of the UK’s native seed-bearing species have already been banked. Two species are particularly set to benefit from the project. The cornflower was once thought of by farmers throughout the UK as a troublesome weed; an action plan is now in place to develop and maintain viable populations at established sites. The cowslip, a traditional “fairy” flower, has been an important medicinal herb since the 17th century, and is also now rare.

The Millennium Seed Bank, like other similar projects around the world, is helping to ensure that our descendants will have access to the rich flora we take for granted.

Blowing in the wind

Seeds can survive changing conditions - cold winters, droughts and forest fires - that may kill the parent plant. The survival of the species is ensured by the mobility of the seeds. Fruits and seeds disperse in many different ways. Aerodynamically efficient, the wispy plumes of the dandelion’s parachute-like fruits and the winged “propellers” from maple and sycamore trees are blown into the air and fly in the wind. Some seeds, such as rosebay willowherb, float in the air for miles in clouds of fluff.

Some species, for example the garden pea and the sesame plant, produce seedpods that burst open when ripe, catapulting the seeds into the air. Coconuts, with a fibrous husk, drop into the sea and float, and may be dispersed for thousands of miles by ocean currents. Some seeds hitch a lift by enclosing themselves in delicious and nutritious nuts and fruits, irresistible to birds and animals which later excrete them far from the parent plant. The squirrel may bury hundreds of acorns for its winter store - and perhaps forget where they all are. Many oak trees have no doubt sprouted from such “forgotten” acorns.

Seeds and fruits can vary greatly in appearance. The “conker” is the seed of the horse chestnut tree; the large spiky fruits, which ripen around September, split open to reveal the beautiful brown nuts. Plants such as the cocklebur use spines or hooks to cling to any walking creature that brushes past the plant; others, for example mistletoe seeds, are enclosed in a sticky casing.

Seeds are made up of two elements: the seed cell containing the genetic material of the plant, and a food supply to nourish the seedling as it begins to grow. The world’s smallest seeds are those that belong to an orchid flower that lives on trees - 992 million of them weigh less than one gram. And the largest seeds, weighing in at 18kg each, are those of the coco de mer coconut palm.

Harvest for health

Many seeds are a rich source of food. From breakfast cornflakes to teatime beans on toast, children eat a range of seeds every day. We eat the enclosing fruits, too. The avocado fruit is the most nutritious in the world; it provides 10 times the energy of a cucumber.

As well as being aesthetically pleasing and the source of a rich variety of tasty food, flowering plants and trees can be good for our health. Research has shown that hospital patients who have a view of trees have fewer complications, require less nursing and spend less time in hospital.

Harvest time can be more than an occasion for celebrating the natural world as a provider of food; we can also consider the beauty and variety of plants. And, on October 14, children can take part in national Seed Gathering Sunday activities, aimed at increasing the range and number of trees in the country.