Let's look at how a tree works. Roots take in water and food from the soil for the tree. Xylem carries water and minerals up from the roots to the leaves. Phloem carries food made in the leaves to the branches, trunk and roots. Sapwood is the tree's pipeline for water moving up to the leaves.

Leaves make food for the tree. They get their green color from a pigment called chlorophyll. Most evergreen trees have needle-shaped leaves. The narrow needles of a Douglas fir can expose as much as three acres of chlorophyll surface to the sun.

Bark is a tree's protection from the outside world. Bark keeps a tree warm in cold and cool in heat, and it keeps insects away. Coast redwood bark is thick and protects the tree from fire. Heartwood is the supporting pillar of the tree.

Evergreen trees stay green all year. A pine tree is one of them. Pine trees carry their seeds in cones. A maple seed has a wing. Squirrels hide acorns by burying them, and that moves oak seeds around from place to place.

The cambium cell layer is the growing part of the trunk. A trunk cut across shows a pattern of rings. The number of rings shows how old a tree or limb is. Some living bristlecone pines are more than 4,000 years old.

Words to know

• xylem: water pipeline
• phloem: food pipeline
• chlorophyll: green pigment
• cambium: growing layer
• evergreen: green all year