Some trees are very old and very tall. Some living bristlecone pines are more than 4,000 years old. The General Sherman Tree is thought to be between 2,200 and 2,700 years old, as of November 2026. Coast redwoods are the tallest trees in the world, as of November 2026. They also take in water from fog, as of November 2026.

Roots take in water and food from the soil for the tree. Most tree roots are in the top three feet of soil. 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.

Leaves make food for the tree. They get their green color from a pigment called chlorophyll. As nights get longer in autumn, trees get a signal that the growing season is ending, and the green chlorophyll fades. Yellow and orange colors in leaves come from carotenoids, which are in the leaf all summer.

Evergreen trees stay green all year. A pine tree is an evergreen tree. 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. Pine trees and other conifers carry their seeds in cones. A maple seed has a wing.

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 central, supporting pillar of the tree. Squirrels hide acorns by burying them, and that moves oak seeds around.

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. The width of a tree's ring changes with the weather and other conditions of that year.

Words to know

• xylem: water pipeline
• phloem: food pipeline
• chlorophyll: green pigment
• carotenoids: yellow-orange pigments
• cambium: growing layer

The short version

A tree grows in its trunk. The cambium cell layer is the growing part of the trunk. Roots take in water and food, xylem carries water up, and phloem carries food from the leaves. A trunk cut across shows rings, and the number of rings shows how old a tree or limb is.

Quick facts

• The cambium cell layer is the growing part of the trunk.
• 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.
• The number of rings shows how old a tree or limb is.
• Coast redwoods are the tallest trees in the world, as of November 2026.