Resins
. Resins, term applied to a group of sticky, liquid, organic substances that usually harden, upon exposure to air, into brittle, amorphous, solid substances. Natural resins are secreted by many plants, appearing on the external surface of a plant after a wound. The resins form protective coatings over the plant wounds, preventing the entrance of pathogenic microorganisms and also excessive loss of sap from the wound. In obtaining natural resins commercially, cuts are made in the tree bark, and the globules of liquid resin that flow from the cut are directed by troughs into collecting buckets. Amber is one of many fossil resins that are often collected from ground deposits. Natural resins are yellow to brown in color. They burn with a smoky flame and exude an aromatic odor. Chemically, they differ from one another in detail, but they all contain carbon, hydrogen, and oxygen. All resins are insoluble in water, as distinguished from the water-soluble gums. Resins are also soluble in alcoh