Arabic, tragacanth, ghatti, karaya and other commercially valuable gums are also exudations of a variety of trees and shrubs. Their hydrophilic and other properties render them useful in the adhesives, beverage, cosmetic, paint, paper-making, pharmaceutical, textile and other industries.
Many of the resins or resin-like substances of the Mediterranean and adjoining regions have been exploited by man from the earliest times. Good examples are myrrh and frankincense with their Biblical associations and purposes. Some were used by the Egyptians in embalming, while mastic and sandarac have long been valued for special paints and varnishes. In the Middle Ages the famous Italian painters made use of them, the actual formulae used being sometimes closely guarded secrets.
Resin tappers in Sumatra induce resin flow in [Shorea javanica] (Dipterocarpaceae) by first opening vertical rows of small (3cm) holes in the tree trunk. After 6-12 months, larger (10-15 cm) holes are opened between the rows of small holes for resin harvest. Informants reported that opium applied to trees increased resin yields. Application of 10% 2-chloroethylphosphonic acid to artificial trunk wounds of [S. javnica] production trees increased resin yields by 110%. Wounds of previously untapped trees exuded no resin in response to the same treatment.