protoxylem lacunae occur in

Options

A. grass stem vascular bundles
B. cladodes
C. underground stems
D. climbers.

Answer

To answer the question "Protoxylem lacunae occur in," follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Protoxylem**:
- Protoxylem is the first-formed xylem in vascular plants, which is responsible for the conduction of water and minerals.

2. **Identify the Context of Protoxylem Lacunae**:
- Protoxylem lacunae are cavities formed when some protoxylem cells disintegrate. This process creates a lysigenous cavity that can store water.

3. **Analyze the Options Given**:
- The options provided are: grass stem, vascular bundles, cladodes, underground stem, and climbers.

4. **Focus on Monocot Vascular Bundles**:
- Protoxylem lacunae are specifically associated with monocot vascular bundles. In monocots, such as grasses, the protoxylem can form lacunae.

5. **Determine the Correct Answer**:
- Since grasses are monocots and their vascular bundles can contain protoxylem lacunae, the correct answer is **grass stem vascular bundles**.

### Final Answer:
Protoxylem lacunae occur in **grass stem vascular bundles**.

---