.............. growth is increase in girth. It is caused by ............. cells.

Answer

**Step-by-Step Solution:**

1. **Identify the Type of Growth**: The question asks about the type of growth that results in an increase in girth. In plants, this type of growth is known as **secondary growth**. This growth occurs in the stems and roots, leading to an increase in their diameter.

2. **Understand the Cells Involved**: The next part of the question requires identifying the type of cells responsible for this secondary growth. The cells that contribute to secondary growth are called **lateral meristematic cells**.

3. **Specify the Types of Lateral Meristematic Cells**: There are specific types of lateral meristematic cells involved in secondary growth, which include:
- **Cork cambium**: This produces cork cells that form the outer protective layer of the plant.
- **Vascular cambium**: This produces new vascular tissues (xylem and phloem) that facilitate transport within the plant.

4. **Final Answer Construction**: Based on the above points, the complete answer to the question is:
- "Secondary growth is an increase in girth. It is caused by lateral meristematic cells."

---