Extrastelar secondary growth takes place by phellogen (option B)

Introduction:
Secondary growth is the increase in girth or thickness of a plant that occurs in woody plants. It is responsible for the development of the secondary tissues, such as secondary xylem, secondary phloem, and periderm. Extrastelar secondary growth refers to the secondary growth that occurs outside the vascular cambium. The vascular cambium is the main meristem responsible for secondary growth, but in some cases, extrastelar secondary growth can also occur.

Explanation:
Phellogen, also known as cork cambium, is a lateral meristem that produces the periderm, which replaces the epidermis in older stems and roots. It is responsible for the formation of the outer protective covering of the plant, known as the cork or bark. The cork cells produced by the phellogen are dead at maturity and provide protection against mechanical damage, water loss, and pathogens.

Key Points:
- Extrastelar secondary growth refers to secondary growth that occurs outside the vascular cambium.
- The vascular cambium is the main meristem responsible for secondary growth.
- Phellogen, or cork cambium, is a lateral meristem that produces the periderm.
- The periderm replaces the epidermis in older stems and roots.
- The cork cells produced by the phellogen provide protection against mechanical damage, water loss, and pathogens.

Conclusion:
Extrastelar secondary growth takes place by phellogen (cork cambium). It is responsible for the production of the periderm, which replaces the epidermis in older stems and roots. The cork cells produced by the phellogen provide protection to the plant against various external factors.