Daniel Ball, age 10, of Gastonia, North Carolina, for his question:

How can you tell the age of a tree?

Each tree grows to its full height and no more. A pin oak may reach 60 feet, but this does not tell us its age. That secret is hidden in its trunk. If the trunk is about one foot wide, the pin oak is fairly young,. It may not grow any taller, but its trunk may grow as wide as two feet. This is because a tree adds layers of new cells around its trunk, every year as long as it lives. The new growth is added just below the bark. In winter the new boxy wooden cells are small and darker. In summer they are larger and lighter.

We see these growth rings when we cut across the trunk of a tree. They are arranged in circles with the tiny ones in the middle and larger and larger ones toward the outside rim. A double ring of lighter and darker wood was added every year and we can count them to learn the age of the tree. Foresters sometimes bore out a sample of wood from a trunk. That way they count the rings without cutting down the tree.