All the cells in a person's body have the same DNA and the same genes. However, the difference between cells in different tissues and organs is that the "expression" of the genes differs between cells. Expression means that the message from the DNA is being copied and made into protein.
There are many answer you have to be specific
The correct answer should be the Periderm.
It is not as simple as this, of course and you would be wise to know that periderm is just a part of the overall concept that is bark, because bark is not a biological term.