Arrange the below four layers in proper order starting from the outermost to the innermost layer after secondary growth has already occurred in a dicot stem.
I. Phellem
II. Wood
III. Phelloderm
IV Vascular cambium

Options

A. `I to II to III to IV`
B. `I to III to II to IV`
C. `IV to III to II to I`
D. `III to II to I to IV`

Answer

To arrange the layers of a dicot stem after secondary growth from the outermost to the innermost layer, we need to identify the correct order based on the structure of the stem. The layers given are:

I. Phellem
II. Wood
III. Phelloderm
IV. Vascular cambium

### Step-by-Step Solution:

1. **Identify the Outermost Layer**: The outermost layer of the dicot stem after secondary growth is the **Phellem** (also known as cork). This layer protects the stem and is formed from the cork cambium.

2. **Next Layer Inward**: Beneath the phellem is the **Phelloderm**. This layer is produced by the cork cambium and lies just inside the phellem.

3. **Wood Layer**: After the phelloderm, we find the **Wood**, which refers to the secondary xylem. This layer is responsible for the transport of water and nutrients and provides structural support.

4. **Innermost Layer**: The innermost layer is the **Vascular Cambium**. This is a meristematic tissue that produces secondary xylem (wood) and secondary phloem, allowing for the growth in thickness of the stem.

### Final Order:
So, the correct order from the outermost to the innermost layer is:
1. Phellem (I)
2. Phelloderm (III)
3. Wood (II)
4. Vascular cambium (IV)

### Answer:
I. Phellem → III. Phelloderm → II. Wood → IV. Vascular cambium

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