What are the rings in a woody stem made up of?

The rings in a woody stem, also known as growth rings or annual rings, are primarily made up of layers of xylem tissue. Each ring represents a year of growth, with the inner part typically consisting of older, darker wood and the outer part made up of lighter, newer wood. The thickness of the rings can vary based on environmental conditions, indicating the growth rate during that year. Additionally, the rings are composed of cellulose, lignin, and other organic compounds that contribute to the stem's strength and structure.