The absorbing and anchoring organ of vascular plants. Roots are simple axial organs that produce lateral roots, and sometimes buds, but bear neither leaves nor flowers. Elongation occurs in the root tip, which is usually 0.004–0.04 in. (0.1–1.0 mm) in diameter and 0.4–4 in. (1–10 cm) long. The older portion of the root, behind the root tip, may thicken through cambial activity. Some roots, grass for example, scarcely thicken, but tree roots can become 4 in. (10 cm) or more in diameter near the stem. Roots may be very long. The longest maple (Acer) roots are usually as long as the tree is tall, but the majority of roots are only a few centimeters long. The longest roots may live for many years, while small roots may live for only a few weeks or months.