Edward Stone (natural philosopher) piece of bark from a willow tree and was struck by its extremely bitter taste. Knowing that the bark of the Peruvian cinchona tree − from which quinine (used in the treatment of malarial fevers) is derived − has a similarly bitter taste, he surmised that the willow might also have therapeutic properties. Stone's interest in willows was due to the ancient "doctrine of signatures" – whereby the cause of a disease offers a clue to its treatment. According to Stone: "As this tree delights in a moist or wet soil, where agues chiefly abound, the general maxim that many
Tree fork forms in a tree and bark is incorporated into the join, this is referred to as an 'included bark junction' or 'bark inclusion'. A common cause of bark being incorporated into the junction is that the junction is braced by the touching of branches or stems set above that junction (in arboriculture, these branch interactions are termed 'natural braces'). Such included bark junctions can be substantially weaker in strength than normal tree forks, and can become a significant hazard in a tree, particularly when the bracing branches are shaded out or pruned out of the tree. Research has shown that