Introduction to the willow tree. One of the most used in American history and prehistory. The inner bark or Cambriam layer of the tree contains a chemical called salicin, the chemical used for what we know as advil. A all natural nsaid painkiller. With the tree bark there are no side effects that goes along with the manufactured over the counter pain killers like stomach or liver issues. The same people who have trouble taking over the counters won't have the same issues. With this bark you can also do something you can't with the manufactured stuff is using topically. All in all one of the most important trees in the herbal medicine world.