Name two underground and subaerial modifications of stem.

Explanation

**Step-by-Step Text Solution:**

1. **Understanding the Question**: The question asks for two types of modifications of the stem, specifically focusing on underground and subaerial types.

2. **Identifying Underground Modifications**:
- **First Modification: Rhizome**
- Definition: A rhizome is a type of underground stem that grows horizontally or parallel to the soil surface.
- Characteristics: It has nodes, internodes, buds, and scaly leaves.
...