What is bark ? Give its importance . Why are certain barks used in medicines ?

Explanation

### Step-by-Step Solution:

1. **Definition of Bark**:
- Bark is defined as the outermost layer of the stem and roots of a woody plant. It serves as a protective covering for the plant.

2. **Importance of Bark**:
- **Protection**: Bark plays a crucial role in protecting the plant. It safeguards the inner tissues from physical damage and environmental factors.
- **Water Retention**: It helps in preventing the loss of water from the plant, which is vital for maintaining hydration and overall health.
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