What is sheathing base and a pulvinus in leaves?

Explanation

### Step-by-Step Solution:

1. **Understanding Sheathing Base**:
- In certain monocotyledonous plants, the base of the leaf expands to form a structure known as the sheathing base.
- This sheathing base partially or fully encircles the stem of the plant, providing support and protection.

2. **Examples of Sheathing Base**:
- Common examples of plants with a sheathing base include grasses and some other monocots.
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