Chenxiang and qinan are essentially the same type of resinous substances, produced by certain trees in the subtropical and tropical regions as a self-defense/healing mechanism when injured or infected. The highest grade of chenxiang/qinan, however, was the result of the wood, for reasons unknown, producing so much of these resins that they eventually choke the life out of the tree. As the tree fibers disintegrate, the resinous substances remain and mature while exposed to the elements. These substances produce strong, complex aromas which have been admired by different cultures through the centuries. While in many other cultures they were mainly used in religious ceremonies, it was in China that they were appreciated in their own right. They were so prized in the Song period that they were already said to be worth their weight in gold, and many poems were written alluding to their quality.