Why a tree makes oud
Oud is the resin-saturated heartwood of the Aquilaria tree. A healthy tree produces none. When the tree is wounded and infected, it floods the injury with resin; the hardened result is agarwood, called oud.
Aquilaria yields nothing while it is sound. Fungus wounds it, the tree answers with resin, and oud is that defence after it hardens.
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