Which one is correct about the cork cambium / phellogen?

Options

A. Usually cortex of stem forms it during secondary growth of stem
B. It is a couple of layers thick
C. It is made up of thin-walled rectangular cells
D. All

Answer

To answer the question "Which one is correct about the cork cambium / phellogen?", we will analyze the information provided in the video transcript step by step.

### Step-by-Step Solution:

1. **Understanding Cork Cambium/Phellogen**:
- The cork cambium, also known as phellogen, is a type of lateral meristematic tissue that is responsible for the production of cork (phellem) and phelloderm during secondary growth in stems and roots.

2. **Origin of Cork Cambium**:
- The cork cambium usually originates from the outer layers of the cortex during secondary growth. It is formed from the cells of the cortex, which are typically rectangular in shape.

3. **Function of Cork Cambium**:
- The cork cambium is referred to as "extra-stelar cambium" because it is located outside the vascular bundles (the stellar system). Its primary function is to produce cork cells that form the protective outer layer of the plant.

4. **Cell Division and Tissue Formation**:
- The cork cambium undergoes periclinal division, which means that the cells divide parallel to the surface. This results in the formation of new cork cells (phellem) on the outside and phelloderm (the inner layer) on the inside.

5. **Characteristics of Cork Cells**:
- Cork cells are characterized by the deposition of suberin, which makes them impermeable to water. This is why cork is often used for sealing bottles and other containers.

6. **Components of the Cork Layer**:
- The cork layer consists of three main components: phellem (cork), phellogen (cork cambium), and phelloderm. Together, these layers provide protection and support to the plant.

### Conclusion:
Based on the analysis above, the correct statement about cork cambium/phellogen is that it is formed from the cortex cells during secondary growth and is responsible for producing cork and phelloderm.