Barkskin(Player's Handbook v.3.5, p. 203)
Level: Nentyar Hunter 1, Druid 2, Ranger 2, Urban Druid 2, Plant 2,
Components: V, S, DF,
Casting Time: 1 standard action
Target: Living creature touched
Duration: 10 min./level
Saving Throw: None
Spell Resistance: Yes (harmless)
Barkskin toughens a creature's skin. The effect grants a +2 enhancement bonus to the creature's existing natural armor bonus. This enhancement bonus increases by 1 for every three caster levels above 3rd, to a maximum of +5 at caster level 12th.
The enhancement bonus provided by barkskin stacks with the target's natural armor bonus, but not with other enhancement bonuses to natural armor. A creature without natural armor has an effective natural armor bonus of +0, much as a character wearing only normal clothing has an armor bonus of +0.