Introduction
Minerals, water and nutrients travel from the soil to other parts of a tree by way of small tube-like tissues called xylem. A similar type of tissue, called phloem, carries food substances down from the tree's leaves. In between xylem and phloem tissue, is the tissue called cambium. Cambium is the growth tissue of the stem that produces new xylem and phloem cells. Each year, as a new layer of xylem cells grows, it wraps around the layer before it. Because each layer is one year's growth of xylem cells, these layers are called annual rings.

Most students already know that you can count the rings on a tree stump to get the age of a tree, but the annual rings contain more information and can be used by scientists to date old wooden structures, tell the weather, etc.

Questions

1. How can we demonstrate the function of xylem and phloem?
2. What do annual rings really tell us?

Materials

• Celery
  Plastic cups
  Food coloring
  Knife
  Lab-aids kit
  Trunk cross-sections (tree cookies)

Procedures

1. Give each group 2 plastic cups. Have students fill the cups about half full of water and add food coloring (two different colors). With the leaves still on the celery, cut a slit up the bottom of the stalk about half way up so that one half can be put in each of the two cups.
2. Let this experiment set overnight for best results.
3. Pass out the 'tree cookies' and let students practice counting the rings.
4. Complete the optional Lab-aids kit on dendrochronology. (Published by Lab-aids, Inc., not included in guide.) Intermediate-aged students will probably need some guidance as they go through the worksheet. However, the activity does give them some interesting insights, especially into archeology and the early history of our country.
5. The next day, examine the celery experiment.

Results
The leaves of the celery should show the two colors of the food coloring on their respective sides. Also, if you cut about a centimeter off the bottom of the celery, the colored xylem will show very well. Be sure that students see this.

Results

1. Why do the leaves turn the color of the food coloring?

Conclusion
The xylem of the celery will transport water up to its leaves. Since the water is colored, the coloring will show up in the leaves.