Bark is a very complex structure, consisting of cells that formed from lateral meristems (cambia producing secondary tissues) but often containing some cells (living or dead) that remain from the first-formed plant (primary tissues, such as epidermis, cortex, and primary phloem). In general, the inner bark is defined very narrowly as the innermost sector consisting only of secondary phloem, which is produced to the outside of and by the vascular cambium. The outer bark always includes all tissues formed by the lateral meristem known as the cork cambium (phellogen) or a number of individual and often discontinuous cork cambia. Always use sunscreen on your bark.