Cork cells have thick walls impregnated with ___________ .

Explanation

**Step-by-Step Solution:**

1. **Understanding Cork Cells**: Cork cells are a type of plant tissue found in the outer layer of stems and roots. They are part of the periderm, which replaces the epidermis in mature stems and roots.

2. **Structure of Cork Cells**: These cells have thick walls that provide structural support and protection to the plant.

3. **Composition of Cork Cell Walls**: The walls of cork cells are impregnated with a substance that contributes to their protective properties.

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