Select an incorrect statement regarding secondary growth in dicot stem or root

Options

A. In dicot stem parenchymatous cells of each medullary ray, lying between the intrafascicular cambium of the adjacent bundles divide and become meristematic and form a strip of cambium called the interfascicular cambium.
B. In dicot stem complete vascular cambium is partly primary and partly secondary in origin.
C. In dicot stem the cells of the cork cambium are rectangular and these cut off cells only on out sides.
D. In dicot roots cells of the pericycle become meristematic and give rise to a few layers of thin-walled rectangular cells. These constitute the Cork cambium or phellogen

Explanation

To determine the incorrect statement regarding secondary growth in dicot stems or roots, let's analyze the provided options step by step.

### Step-by-Step Solution:

1. **Understanding Medullary Rays**:
- In dicot stems, parenchyma cells of each medullary ray (also known as PIT rays) extend between the vascular bundles. This statement is correct as medullary rays play a role in the transport of nutrients and water.

**Hint**: Medullary rays connect vascular bundles and are important for the movement of substances within the plant.

2. **Interfascicular Cambium**:
- The interfascicular cambium forms from the division of cells lying between the intrafascicular cambium of adjacent vascular bundles. This statement is also correct, as interfascicular cambium contributes to secondary growth.

**Hint**: Interfascicular cambium is crucial for the formation of new vascular tissue during secondary growth.

3. **Cork Cambium Function**:
- The statement claims that the cells of the cork cambium are rectangular and that they only cut off cells on the outside. This is incorrect because cork cambium (or phellogen) produces cells on both the outside (cork) and the inside (phelloderm).

**Hint**: Remember that cork cambium contributes to the protective outer layer of the plant by producing cells in both directions.

4. **Meristematic Cells in Dicot Roots**:
- The statement about dicot root cells of the pericycle becoming meristematic and forming thin-walled rectangular cells (cork cambium or phellogen) is correct. This process is essential for secondary growth in roots.

**Hint**: The pericycle is important for the formation of new tissues in roots, aiding in secondary growth.

### Conclusion:
After analyzing all the statements, the incorrect statement is the third one regarding cork cambium. Therefore, the answer is:

**Option 3 is the incorrect statement regarding secondary growth in dicot stems or roots.**