15/01/2026
a detailed anatomical breakdown of a tree trunk, using a cutaway diagram to show the various layers and sections. It illustrates how a tree grows and protects itself, moving from the innermost core to the outer protective bark.
1. THE CORE LAYERS (THE WOOD)
The central part of the log represents the Xylem, which is divided into two main functional areas:
• Pith: The absolute center of the trunk. This is the oldest part of the tree, consisting of soft, spongy tissue that was essential during the tree's first year of growth.
• Heartwood: The dark, inner ring of wood. This area is composed of dead cells that have been plugged with resins and tannins. While it no longer transports water, it provides the primary structural strength for the tree.
• Sapwood: The lighter-colored wood surrounding the heartwood. Unlike heartwood, this layer contains living cells and is responsible for transporting water and minerals from the roots up to the leaves.
• Rays: These are the horizontal lines extending from the pith toward the bark. They allow for the radial transport of nutrients and water across the grain.
2. THE GROWTH AND TRANSPORT LAYERS
Moving outward from the sapwood, we find the thin, highly active layers responsible for the tree’s expansion:
• Vascular Cambium: Shown as the thin green layer. This is a microscopic layer of meristematic tissue (growth cells). It produces new xylem (wood) toward the inside and new phloem (inner bark) toward the outside.
• Living Phloem (Inner Bark): The layer just outside the vascular cambium. Its primary job is to transport sugars produced during photosynthesis from the leaves down to the rest of the tree.
3. THE OUTER PROTECTION (THE BARK)
The outermost sections serve as the tree’s "skin," protecting it from insects, disease, and weather:
• Periderm: This includes the Cork Cambium (the layer that produces bark) and the Cork itself.
• Cork: The tough, dead outer layer. It is waterproof and provides insulation and physical protection.
• Bark: Collectively, the term "bark" refers to every layer outside the vascular cambium (the living phloem, cork cambium, and cork).
4. ANATOMICAL PERSPECTIVES
The diagram also labels the three primary ways wood can be cut or viewed:
• Cross Section (Transverse): A cut perpendicular to the trunk (looking down at the rings).
• Radial Section: A longitudinal cut that passes through the center (pith) of the log.
• Tangential Section: A longitudinal cut that is perpendicular to the rays (not passing through the pith).
