Bamboo,grass and mint stem elongate by the activity of intercalary meristemHence (C) is the correct answer.

Intercalary Meristems are responsible for the elongation of bamboo, grass, and mint stems.

Intercalary Meristems
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Intercalary meristems are a type of meristematic tissue found in plants. They are located at the base of the internodes, which are the regions between the nodes of a stem. The primary function of intercalary meristems is to promote elongation growth in stems.

Role in Elongation
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The intercalary meristems are responsible for the elongation of stems in bamboo, grass, and mint plants. They contribute to the rapid elongation of these plants, allowing them to reach their maximum height.

Key Differences from Other Meristems
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1. Location: Intercalary meristems are located at the base of internodes, while apical meristems are found at the tips of stems and roots.
2. Types of Growth: Apical meristems promote primary growth, which is responsible for the increase in height and length of stems and roots. On the other hand, intercalary meristems contribute to intercalary growth, which leads to the elongation of stems.
3. Cell Division: Intercalary meristems primarily undergo cell division in the longitudinal direction, resulting in the elongation of the stem. In contrast, apical meristems undergo cell division in all directions, leading to the growth of various plant tissues.

Conclusion
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In conclusion, bamboo, grass, and mint stems elongate due to the activity of intercalary meristems. These meristems are located at the base of the internodes and promote elongation growth in plants. Understanding the role of intercalary meristems helps us comprehend the unique growth patterns of different plant species.