If you can find a tree which has been cut down，you will see many rings，or circles，on the base of the trunk.By learning to read these rings，you can find out about the tree's life.

The number of rings tells you how old the tree is.Each year，new wood is formed on the outside of the tree.This new wood is light in color when the tree is growing in spring and summer，and dark in winter when the tree is not growing much.So，if you count the rings of dark­or­light colored wood，you can often find out how old the tree is.

You can also tell which years have been good years and which years have been bad years.When the light­colored rings are very wide，it means that the tree has been growing quickly that year.If the rings are narrow，it has been growing slowly.If the rings on a tree trunk were greatly magnified，you would be able to see why the rings are light­colored when the tree is growing quickly and dark­colored when the tree is growing slowly.The tree trunk is made up of microscopic tubes，like some pipes，carrying water from the soil，through the trunk，and up to the leaves.They are wide and thin­walled when the tree is growing quickly and they are carrying a lot of water.They are narrow and stuck together when the tree is not growing so quickly.

When a tree is old，the tubes in the centre of the tree don't carry water.The walls of the tubes have become thick with materials which have stuck along them over the years，forming a kind of wood called"heartwood"．This kind of wood is darker in color than the young，growing wood on the outside of the tree.

You don't very often see whole tree trunks which have been cut across.But once you learn to read a cross section of the wood，you can see much more in wood which has been used to make boxes，houses and other things.

In most wood，instead of seeing the trunk cut across，you are seeing it cut along its length.Because you don't see the whole tree，you can't tell how old it is.

Title：__20__of a Tree

General information Old trees Items Facts Items Facts Where can rings be seen On the __21__of a trunk The tubes in the centre of the tree Don't carry water The__22__of rings Helps us know about its age The walls of the tubes Become

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Form __24__ __25__light­colored rings Show the tree grows quickly Narrow__26__

rings Mean the tree grows slowly