Ginseng, known as Ren-sen or "man root" to the Chinese, has been labeled by researchers as an "adaptogen" because it has the intrinsic ability to normalize body functions. The "adaptogenic" effects are thought to be caused by the presence of ginsenosides or tetracyclic terpenoids, the major constituents of ginseng. Researchers have identified 28 different ginsenosides, in varying percentages among the panax species, although 6 (Rb1, Rb2, Rc, Rd, Re, Rg1) are the most significant. The levels vary due to the age of the plant, soil quality, time of harvest, plan part and other environmental factors inherent to the growing region. The precise type and ratio of ginsenosides present can only be determined through HPLC (High Pressure Liquid Chromatography) testing. All parts of the plant may contain ginsenosides; the roots may contain up to 5% but levels are more commonly in the 2-3% range.