Which one of the following tissues is responsible for increase of girth in the stem of a plant?
Lateral meristem
Understanding Plant Growth and Stem Girth
The question asks to identify the plant tissue responsible for the increase of girth in a plant's stem. This process is known as secondary growth, which leads to the thickening of stems and roots.
Types of Plant Meristems and Their Roles
Plants grow through the activity of meristems, which are regions of actively dividing cells. Meristems can be classified in different ways, including by their location and function:
- Apical Meristems: Located at the tips of shoots and roots, responsible for primary growth (increase in length).
- Intercalary Meristems: Found at the nodes or bases of leaves (e.g., in grasses), also contributing to elongation.
- Lateral Meristems: Located on the sides (lateral) of the plant body, responsible for secondary growth (increase in diameter or girth). The main lateral meristems are the vascular cambium and the cork cambium.
Analysis of Options for Stem Girth Increase
Let's analyze the given options in the context of stem thickening:
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Tracheid:
Tracheids are specialized cells found in the xylem. Their primary function is water transport and mechanical support. They are mature cells and do not divide to cause an increase in girth.
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Pericycle:
The pericycle is a layer of cells located just inside the endodermis in the vascular cylinder of roots and stems. While the pericycle can contribute to secondary growth by forming lateral roots and sometimes participating in the formation of vascular cambium, it is not the primary meristematic tissue directly responsible for the overall increase in stem girth.
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Intercalary meristem:
Intercalary meristems are responsible for the elongation of stems and leaves, particularly in monocots like grasses. They are not involved in increasing the diameter or girth of the stem.
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Lateral meristem:
Lateral meristems, namely the vascular cambium and cork cambium, are the key tissues responsible for secondary growth. The vascular cambium produces secondary xylem (wood) and secondary phloem, adding layers internally, while the cork cambium produces cork tissue externally. Both activities contribute significantly to the increase in stem girth.
Conclusion on Stem Girth Increase
Based on the functions of different plant tissues, the lateral meristem is the tissue primarily responsible for the increase of girth in the stem of a plant through secondary growth.
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