The portion of the trunk having inner annular rings surrounded by the pith is called:
Anatomy of a Tree Trunk
To understand timber, it's essential to know the different layers of a tree trunk, starting from the center and moving outwards.
- Pith: The absolute central part of the trunk. It's the oldest and often softest part of the tree.
- Heartwood: Surrounds the pith. It consists of dead cells and provides the main structural support to the tree. It is dark, hard, and durable.
- Sapwood: This layer is between the heartwood and the cambium layer. It is the living part of the wood, responsible for transporting sap. It's lighter in color and less durable than heartwood.
- Cambium Layer: A very thin, watery, and sticky layer between the sapwood and the inner bark. This is where new wood cells (annual rings) are formed each year.
- Bark (Inner & Outer): The outermost protective layer of the tree.
📝 Detailed Analysis of the Options
(a) Cambium
The cambium layer is a very thin layer responsible for growth, located much further out from the center, between the sapwood and the bark. It is not the inner portion of the trunk.
(b) Bark
The bark is the outermost protective layer of the tree trunk. It is the furthest layer from the pith.
(d) Sapwood
Sapwood is the layer that surrounds the heartwood. While it contains annular rings, it is the outer portion of the main wood body, not the inner portion surrounding the pith.
(c) Heartwood
This is the correct answer. The heartwood is the dense, inner part of the tree trunk that surrounds the central pith. It is formed as the sapwood hardens and its cells die. This portion contains the inner annual rings and provides the primary mechanical support for the tree.
📊 Layers of a Tree Trunk (from center outwards)
| Layer | Location | Primary Function |
|---|---|---|
| Pith | Innermost central core | Original sapling stem |
| Heartwood | Surrounds the pith | Structural support (strong, dead wood) |
| Sapwood | Surrounds the heartwood | Sap conduction (living wood) |
| Cambium | Between sapwood and inner bark | Growth (forms new cells) |
| Bark | Outermost layer | Protection |
💡 Study Tips
- Think "Heart" of the Tree: The heartwood is at the center, or "heart," of the trunk's structural core, right next to the pith.
- Visualize the Layers: Imagine cutting a tree down. The very center is the pith. The large, dark, hard area around it is the heartwood. The lighter ring around that is the sapwood. The very outside is the bark.
- Sap travels in Sapwood: This is an easy way to remember the function of sapwood and distinguish it from the non-living heartwood.