As secondary growth proceeds, in a dicot stem, the thickness of

Options

A. heartwood increases
B. sapwood increases
C. both increase
D. both remain the same

Explanation

### Step-by-Step Solution:

1. **Understanding Secondary Growth**: Secondary growth in dicot stems refers to the increase in thickness or girth of the stem due to the activity of the vascular cambium and cork cambium. This process leads to the formation of secondary xylem (wood) and secondary phloem.

2. **Formation of Heartwood and Sapwood**:
- **Heartwood**: As secondary growth continues, the inner layers of secondary xylem (wood) become heartwood. This part of the wood is no longer involved in the conduction of water and minerals; instead, it becomes filled with substances like tannins, resins, and oils, which provide strength and durability.
- **Sapwood**: The outer layers of secondary xylem, known as sapwood, remain functional and are involved in the conduction of water and nutrients.

3. **Changes During Secondary Growth**:
- As the tree ages and secondary growth continues, the heartwood increases in size as more and more inner layers of xylem are converted into heartwood.
- The sapwood may also increase in thickness, but its primary function remains the conduction of water.

4. **Conclusion**: Given that heartwood increases in thickness as secondary growth proceeds, the correct answer to the question is that the thickness of heartwood increases.

### Final Answer:
The thickness of heartwood increases as secondary growth proceeds in a dicot stem.

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