What is the sequence of tissue from outside to inside in periderm ?

Options

A. Phellem - phelloderm - phellogen
B. Phellem - phellogen - phelloderm
C. Phellogen - phellem - phelloderm
D. Phelloderm - phellogen-phellem

Answer

To determine the sequence of tissues from outside to inside in the periderm, we need to understand the structure and development of the periderm in dicot stems. The periderm consists of three main components: cork cambium (also known as phellogen), cork (phellem), and secondary cortex (phelloderm). Here’s the step-by-step breakdown:

### Step-by-Step Solution:

1. **Identify the Cork Cambium (Phellogen)**:
- The outermost layer of the periderm is the cork cambium, also referred to as phellogen. This tissue is responsible for producing new cells.

2. **Cork Formation (Phellem)**:
- The cork cambium (phellogen) undergoes periclinal division, which means it divides parallel to the surface. This division produces cork cells, known as phellem, on the outer side.

3. **Secondary Cortex Formation (Phelloderm)**:
- In addition to producing cork on the outer side, the cork cambium also produces phelloderm, which is the secondary cortex, on the inner side.

4. **Sequence of Tissues**:
- Therefore, the correct sequence of tissues from outside to inside in the periderm is:
- **Phellum (Cork)** - outer layer
- **Phelloderm (Secondary Cortex)** - inner layer
- **Phellogen (Cork Cambium)** - the layer that produces the other two.

### Final Sequence:
- The sequence from outside to inside in the periderm is: **Phellum → Phelloderm → Phellogen**.