The correct answer is option 2: Cambium. The tissues responsible for the secondary growth of plants are known as vascular cambium and cork cambium. These tissues are found in the stems and roots of woody plants and are responsible for increasing the girth or thickness of the plant over time.

The vascular cambium is a type of lateral meristem that produces new cells towards the inside of the stem or root. These cells differentiate into secondary xylem (wood) towards the center of the plant and secondary phloem towards the outside. This process of producing new xylem and phloem layers leads to the increase in the girth of the plant.

On the other hand, the cork cambium is responsible for the production of cork cells towards the outside of the stem or root. Cork cells form the protective outer bark of the plant and help in preventing water loss and protecting the underlying tissues.

Therefore, the cambium tissues, specifically the vascular cambium and cork cambium, are responsible for the secondary growth of plants. Alert - Correct answer should be Option 2