Resinous trees are trees that produce a sticky substance called resin. This resin serves various purposes, such as protecting the tree from pests and diseases. Common examples of resinous trees include pine, fir, and spruce. The resin can also be harvested for use in products like varnishes and incense. The resin is typically found in specialized ducts within the tree's bark. When the tree is injured, it secretes resin to seal the wound and prevent further damage. This natural defense mechanism is crucial for the survival of resinous trees in their environments.