In the following how the sap wood is converted into heart wood

Options

A. By tylosis formation
B. By deposition of extractives
C. By degeneration of protoplast of living cells
D. All of the above

Answer

### Step-by-Step Solution:

1. **Understanding Sapwood and Heartwood**:
- **Sapwood**: This is the outer, lighter-colored part of the tree trunk. It is responsible for the conduction of water and nutrients from the roots to the leaves and serves as a storage area for extra food.
- **Heartwood**: This is the central core of the tree trunk. It is composed of older, non-living cells that have become dense and are generally darker in color. Heartwood is formed from the aging of sapwood.

2. **Process of Conversion**:
- The conversion of sapwood into heartwood involves several physiological changes:
- **Programmed Cell Death**: The parenchyma cells in the ray and axial regions of the sapwood undergo programmed cell death, leading to the degeneration of their protoplasm.
- **Decrease in Metabolic Activity**: As the cells die, their metabolic activities decrease, which contributes to the transition from living sapwood to non-living heartwood.
- **Deposition of Extractives**: Various substances, such as resins and tannins, are deposited in the wood. These extractives contribute to the durability and color of heartwood.
- **Tylosis Formation**: Tyloses are outgrowths from living parenchyma cells that can protrude into xylem vessels. They form in response to stress or pathogen infection and help to block the vessels, preventing further damage.

3. **Conclusion**:
- The conversion of sapwood to heartwood is a complex process that includes all the factors mentioned: tylosis formation, deposition of extractives, and degeneration of protoplasts of living cells. Therefore, the correct answer to the question is **"All of the above."**