How plants survive
Imagine that you are standing in a field. It is summer and there is tall grass around you and there are the bright red flowers of poppies sticking up above the grass. At the edge of the field is an oak tree. The poppy plant and the oak tree are very different in size and they are also very different in how they survive.

If you had visited the field at the beginning of the year you would have seen the oak but there would not have been any sign of the poppy. Even so, the poppy would have been there but only in the form of a seed. A poppy seed is very small. It is little more than a speck of dust, yet inside it contains a tiny plant and food store just like all seeds. Inside its protective seed coat the tiny plant remains safe from the harsh weather conditions in the field.

The oak tree keeps safe from the harsh winter conditions in a different way from the poppy. Oak trees have woody stems, which grow from year to year, and the plant can live for centuries. Its trunk and branches are covered in bark, which is an insulating material. The winter air is much colder than the inside of the tree but the bark prevents the warmth from inside the tree escaping. If the heat did escape, the tree would freeze and die.

In the spring both plants become active. The poppy seed germinates and the seedling begins to grow up amid the grass. The buds on the oak tree burst open and the leaves push out and spread their green surfaces to the Sun. The leaves of both plants make food. They use the food to help them grow and produce their reproductive organs.

The reproductive organs of the plants are contained in their flowers. The oak tree flowers first - near the end of May. It produces separate male and female flowers. The flowers form groups called catkins. The male flowers release their pollen into the air and it is carried to the stigmas of oak trees in a nearby wood. The female flowers receive pollen from other oak trees later, carried in the wind. The poppy flowers about a month after the oak. It has its male and female reproductive organs in the same flower. Insects visit the poppy for nectar and take away pollen from its stamens. Later its stigma collects pollen from more visiting insects.

Through the summer, the poppy and oak use some of the food they have made to grow their fruits and seeds. The fruit of the oak is a dry nut called an acorn. Each acorn contains a seed. The fruit of the poppy is a structure like an upside-down salt pot. On its top is a ring or hole like portholes in a ship. For now, the holes are clamped shut, but inside the fruit, large numbers of tiny seeds are forming.

When the plants are ready to disperse the seeds, the oak simply drops its acorns while the poppy uses the wind in an unusual way. The holes in the top of the poppy fruit open. The fruit is on a long bendy stem, which sways easily when the wind blows on it. As the stem sways, the fruit shakes out its seeds and they fall to the ground some distance away.

When the poppy plant has dispersed its seed, it dies. By contrast, when the oak has dispersed its seeds it prepares to survive the winter. First, it draws in all nourishment from its leaves. At this time the green substance, which has trapped sunlight for food-making, breaks up and lets the browns and reds of other substances colour the leaves. Next, the oak seals up the water pipes, which connect the leaves to the twigs. As the leaf dries out, it snaps off the twig and falls away.

Next year, the oak will produce flowers once more but it will be the new poppies that bring colour to the field of grass in the summer.

Do plants either live for one year or for many years?
Many plants have life cycles like this. A plant that completes its life cycle in a year, like the poppy, is called an annual plant. A plant that has a life cycle which lasts many years, like the oak, is called a perennial plant. Some plants, like a common weed called the shepherd's purse, completes its life cycle in a few weeks. These plants are called ephemerals. In suitable conditions, the shepherd's purse can grow all year round and can be found flowering in every month. Some plants have a life cycle that takes two years. They are called biennials. The carrot is an example of a biennial. In the first year it stores food in its root. In the following year it uses the stored food to make leaves and flowers. When it has produced seeds and fruits it dies. Other root vegetables, like the parsnip and beet, are biennials.

Does the oak tree produce flowers and acorns in its first year?
No. The oak may take up to fifty years before it produces flowers and acorns. If you know of an oak which does not produce acorns, it is probably too young. If you germinated the seed in an acorn today and took care of the plant, you would probably be sixty before you saw it produce any acorns.

If an oak tree just drops its acorns how are they dispersed?
The oak relies on animals, like squirrels and jays, collecting the acorns and storing them away for winter. As the animals make a large number of stores they may forget where they all are. The acorns in forgotten stores can then germinate and grow into seedlings away from the parent plant.

Do all perennials have woody stems?
No. Many plants have stems that die back in the autumn. The plant survives underground as a root, bulb, corm or tuber. The dandelion is a perennial and has a root like a carrot in which to store food. The daffodil has a bulb. The crocus has a corm and the potato has a tuber. Grass is also a perennial though its shoots do not die back completely but form a short leafy mat in the winter.