Which of the following meristems is responsible for extrastelar secondary growth in dicotyledonous stem

Options

A. Interfascicular cambium
B. Intercalary meristem
C. Phellogen
D. Intrafascicular cambium

Answer

To determine which meristem is responsible for extrastelar secondary growth in dicotyledonous stems, we can follow these steps:

### Step 1: Understand the Types of Meristems
Meristems are regions in plants where cells are actively dividing. There are three main types of meristems:
- **Apical Meristem**: Located at the tips of roots and shoots, responsible for primary growth (length).
- **Lateral Meristem**: Responsible for secondary growth (width), includes vascular cambium and cork cambium.
- **Intercalary Meristem**: Found at the base of leaves or internodes, contributes to growth in length.

### Step 2: Identify the Meristem Types Relevant to Secondary Growth
In dicotyledonous plants, secondary growth is primarily due to:
- **Vascular Cambium**: A lateral meristem that produces secondary xylem (wood) and secondary phloem.
- **Cork Cambium (Phthalogen)**: Another lateral meristem that produces cork cells, contributing to the protective outer layer of the stem.

### Step 3: Focus on Extrastelar Secondary Growth
Extrastelar secondary growth refers to the growth that occurs outside the vascular bundles. The cork cambium (phthalogen) is responsible for this type of growth as it forms the outer protective layer (cork) of the stem.

### Step 4: Eliminate Other Options
- **Intrafascicular Cambium**: Located between xylem and phloem within the vascular bundles, not responsible for extrastelar growth.
- **Intercalary Meristem**: Involved in elongation but not in secondary growth.
- **Intrafascicular Cambium**: Similar to intrafascicular cambium, it does not contribute to extrastelar growth.

### Conclusion
The meristem responsible for extrastelar secondary growth in dicotyledonous stems is the **Cork Cambium (Phthalogen)**.

---