Heart wood is dark ............... in colour.

Answer

**Step-by-Step Solution:**

1. **Understanding Heartwood**: Heartwood is the inner part of the secondary xylem in a plant. It is formed as the plant matures and is surrounded by sapwood, which is the outer, functional part of the xylem.

2. **Characteristics of Heartwood**: Heartwood is a modified and non-functional region of the xylem. Unlike sapwood, which is involved in the conduction of water and nutrients, heartwood consists of dead cells.

3. **Composition of Heartwood**: The heartwood is primarily made up of dead elements, which are highly lignified. Lignin is a complex organic polymer that provides rigidity and resistance to decay.

4. **Color of Heartwood**: Due to its composition and the presence of lignin, heartwood typically has a darker color compared to sapwood. Specifically, heartwood is dark brown in color.

5. **Conclusion**: Therefore, the answer to the question is that heartwood is dark brown in color.

**Final Answer**: Heartwood is dark brown in color.

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