Barkskin

Barkskin was a druid evocation and a transmutation or alteration spell that toughened the skin to a bark-like consistency.

Effects
Barkskin toughened the skin of the creature touched, giving it natural armor. In general, the quality of the armor improved the higher the caster's power. The barkskin evocation drew upon the caster's constitution for the strength of the armor&mdash;a tougher caster could bestow tougher armor. The spell would not stack with any other effect that increased natural armor.

Components
The older versions of this spell required some bark from an oak tree in addition to the verbal and somatic components. All versions of the spell (but not the evocation) required the use of the caster's holy symbol or divine focus.