Question

As the plants grow older what are the changes the outer protective tissue undergoes?

Answer 1

As the plants grow older, the outer protective tissue undergoes the following changes:
1. Epidermis of the stem is replaced by a strip of the secondary meristem.
2. Cells present on the outside are separated from this layer which forms the bark of the tree (cork layer). The cork cells thus formed contain a chemical called suberin in their walls and are dead.