Microscopic Identification Characteristic of Agarwood and Its Imitation

Agarwood is a kind of combination of wood and organic resin with special aroma. When the injured trees of Thymelaeaceae Aquilaria are invaded by specific micro organisms, a series of interactions occur between them, eventually forming resin mainly composed of "sesquiterpenes" and "chromones". Agarwood is mainly formed in Guangdong, Guangxi, Yunnan and Hainan Province of China, and southeast Asian countries such as Indonesia, Malaysia, Brunei amd Vietnam. Seven kinds of agarwood samples from eight countries and regions and four kinds of agarwood imitation samples have been investigated by photomicrograph. The result shows that no matter the origin and development degree of agarwood, since they are all formed by trees of Thymelaeaceae Aquilaria, their microstructures have significant coherence. All of them are composed of wood fibers, vessels, interxylary phloems and rays. On the cross section, wood fibers are light yellow, round or nearly round, arranged in rows, 20-50 μm in diameter. The rays are arranged parallel to the rows of wood fibers, 2-6 cells wide, scatteredly interspersed in the rows of wood fibers, and the colour is dark brown. Vessels are round or nearly round, 50-150 μm in diameter, existing alone or 2-4 in a row, arranged parallel to the rows of Wood fibers. Empty vessels are white, and some vessels are dark brown for being filled with resin. Interxylary phloems are elliptical or banding, 0.2-0.8 mm long, perpendicular or nearly perpendicular to the wood fibers. Most of them are dark brown for being filled with resin. Among the imitation samples, one is made of agallochum without resin, which has the same microstructure with agarwood, but there are no resin filling in it. The outer colour of this fake sample is slightly darker, and the inner colour is white. The other three imitations are all wood imitations of other tree species, whose appearances are dark brown, with woody pattern, but microscopic observation shows no unique structure of agarwood, which are quite different from agarwood.