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B Researchers from China and the United States have found what makes ginkgo (trees live for more than 1,000 years, according to a newspaper report.Researchers from Beijing For- estry University,the University of North Texas and some other Chinese research institutions reported in the US magazine Pro- ceedings of National Academy of Sciences that they analyzed 34 ginkgo trees and divided them into three groups according to their ages. Compared with adult trees,the ancient trees,aged from 193 to667 years,have thinner cambium(新生组织)cell layers. Cambium cells are layers of stem cells between the internal wood and external bark changing into other tissues.