In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. ... Plants secrete resins for their protective benefits in response to injury. The resin protects the plant from insects and pathogens.
If you have regularly handled or touched the bark or cones of pine, spruce or larch, you know about the fragrant "sticky" resin they copiously ooze. That resin is contained in ducts or blisters that run through the bark and wood and diminish in size and number as they enter roots and needles. Hemlocks, true cedars, and firs have resin mainly restricted to the bark.
Wound trauma to a tree can stimulate the production of "traumatic resin canals" that help in containing the injury and help in healing any resulting infection. Resin-laden blisters contained in the conifer secrete the light liquid, which immediately loses oils to evaporation and forms a heavy solid scab. It is interesting to note that this reaction to trauma by a tree is used in the manufacturing process of certain commercial resins and essential oils by stimulating resin flow by inflicting a purposeful injury or bark irritation (see tapping below). The production of resin is very common in nature, but only a few plant families can be considered of commercial importance to resin collectors. These important resin producing plants include the Anacardiaceae (gum mastic), Burseraceae (incense tree), Hammamelidaceae (witch-hazel), Leguminosae, and Pinaceae (pine, spruce, fir, true cedar).
