The smell of Agar wood is complex and pleasing, with few similar in nature and not, due to this the agarwood and its essential oil gained a strong cultural and religious significance in ancient civilizations around the world, beeing even mentioned in one of the oldest written texts, the Sanskrit Vedas of India. There are fifteen species of Aquilaria and eight of them are known for the production of agarwood. Formation of agarwood occurs in the trunk and roots of trees that have been infected by a parasite, fungus ascomyces Phaeoacremonium parasitica. In response, the tree produces a resin high in volatile organic compounds which helps to suppress or retard fungal growth, a process called tylosis. While the unaffected wood of the tree is relatively light in color, the resin dramatically increases the mass and density of the affected wood, changing its color from a light beige to dark brown or black. The resin embedded wood is commonly called Gaharu, jinko, aloeswood, agarwood, or oud and is valued in many cultures for its scent. Besides the production of incense and fragrances, is also used in Emir's palaces to show them respect or in some particular ceremony of welcome for important guests, in these situations some pieces of oud are burned in braziers near the dresses to let them absorb the smoke (the women do the same with their hair). The reasons why oud is so rare and expensive are the scarsity of trees and that the trees must be attacked by this particular mould.