Let's follow the water through a tree. Roots take in water and food from the soil for the tree, and xylem carries water and minerals up from the roots to the leaves. Sapwood is the tree's pipeline for water moving up to the leaves. Plants lose most of the water their roots take in to the air through their leaves, a process called transpiration. Phloem carries food made in the leaves to the branches, trunk and roots.

The cambium cell layer is the growing part of the trunk. As new rings of sapwood form, the inner cells of older sapwood turn into heartwood, which is the central, supporting pillar of the tree. A heartwood post only 12 inches long and 1 by 2 inches across can hold up twenty tons. A trunk cut across shows a pattern of rings, and 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.

Most tree roots are in the top three feet of soil, and a tree's roots often spread out much wider than its crown. Giant sequoia roots are shallow but spread wide. Tree roots give fungi food the tree has made, and the fungi give back water and minerals. Mycorrhizae are partnerships between fungi and roots that help the tree take up water and nutrients.

Evergreen trees stay green all year, and a pine tree is an evergreen tree. Pine trees and other conifers carry their seeds in cones, and male cones are small and hold pollen. A maple seed has a wing. Squirrels hide acorns by burying them, and that moves oak seeds around.

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

Coast redwoods are the tallest trees in the world, as of November 2026, and the tallest known coast redwood is about 380 feet tall, as of November 2026. Coast redwoods also take in water from fog, as of November 2026. Coast redwood bark is thick and protects the tree from fire. Fire is part of the life cycle of giant sequoias, and the General Sherman Tree is thought to be between 2,200 and 2,700 years old, as of November 2026. Some living bristlecone pines are more than 4,000 years old.

Words to know

• transpiration: leaf water loss
• xylem: water pipeline
• phloem: food pipeline
• heartwood: central pillar
• mycorrhizae: root-fungus partnerships