Well not all tree trunks are brown! What trees can you think of that have trunks of other colors such as; red, white, green or black? How about these trees: Madrone, Manzanita, Eucalyptus, Fig? Well I must admit that most tree trunks are brownish. This is because the trunk of the tree is covered with "bark". The bark you see on the outside is composed of dead tissue and usually occurs in layers. This dead tissue is usually brownish due to oxidation caused by the sun and air. Also it contains tannin which is brown. If you scrape off the dead layer of bark you may see a different color in the inner bark.

On your way home from school today, look at all the tree trunks you can. What colors are they?Can you find any trees with white bark? Are there any that are green, or nearly black? There are many kinds of trees, so there are many kinds of bark. A lot of bark is a brownish-gray because the outer layer of bark is made of dead tissue. If you look at unpainted wood that has been out in the weather for a few years, you will see a similar color. Why would it be to the tree's advantage to have an outer covering of dead material?

If you painted a dot on the side of a tree and came back 10 years later, would the spot have moved up? (hint: does a swing hanging from a branch get higher off the ground year after year?) One a tree grows is by adding parts at the ends of itself. Another is by adding layers to make it thicker. If only live cells can divide, and the outer bark is dead, where is the cell division (mitosis) happening? Try (or imagine) this, partially blow up a balloon. Clip the end closed, but don't tie it. (A binder clip should work.) Now make a 'bark' by spreading mud or a flour and water paste on the balloon. Let it dry for a while. Now blow the balloon up a little more. What happens to the 'bark'? Does this expalain the pattern of bark on some
trees?