Secondary growth in plants

Secondary growth is the growth of the plant in thickness. It usually occurs in dicotyledonous plants. In this process, the stem or root of the plant increases in girth and thickness. This growth is a result of the formation of secondary tissues called secondary xylem, secondary phloem, and periderm.

Secondary xylem

Secondary xylem is formed by the vascular cambium, which is a lateral meristem. It is located between the primary xylem and the primary phloem. The cells of the vascular cambium divide to form secondary xylem towards the inside of the stem or root. The secondary xylem is composed of tracheids, vessels, and fibers. These cells are dead and provide mechanical support to the plant.

Secondary phloem

The vascular cambium also forms secondary phloem towards the outside of the stem or root. The secondary phloem is composed of sieve tubes, companion cells, and fibers. The sieve tubes transport the food produced by the leaves to the rest of the plant. The companion cells provide support to the sieve tubes.

Periderm

The periderm is formed by the cork cambium, which is another lateral meristem. It replaces the epidermis of the plant with thicker and tougher cells. The periderm provides protection to the plant against mechanical damage and water loss.

Bark

The bark is the outermost layer of the stem or root of the plant. It is composed of the periderm, secondary phloem, and some tissues of the primary phloem and cortex. The bark provides protection to the plant against environmental stress and diseases.

Answer

The correct answer is option 'A' because bark includes secondary phloem and periderm but not secondary xylem.