Of the more than 250,000 known plant species, less than one percent have been thoroughly tested for medical applications. Yet out of this tiny portion have come 25 percent of our prescription medicines. The U.S. National Cancer Institute has identified 3,000 plants from which anti-cancer drugs are or can be made. This includes ginseng (Panax quinquefolius), Asian mayapple (Podophyllum hexandrum), western yew (Taxus brevifolia), and rosy periwinkle. Seventy percent of these 3,000 come from rain forests, which also are a source of countless other drugs for diseases and infections. Rain forest plants are rich in so-called secondary metabolites, particularly alkaloids, which biochemists believe the plants produce to protect them from disease and insect attack. However, with the current rate of rain forest destruction, raw materials for future medicines are certainly being lost. Also, as tribal groups disappear, their knowledge of the properties and uses of these plants species will be lost.