American elms (榆树) are dying and a fungus (真菌) is to blame. The streets in your neighborhood may have once been lined with huge elm trees that died from this plague, called Dutch elm disease. At one time, American elms were common from the East Coast to the Great Plains. But because of this disease, today they are hard to be found. Dutch elm disease began infecting American trees in 1930. A freighter (货船) brought elm logs from France to New York City, there railroad cars carried the logs to factories in Cleveland and Columbus, Ohio. A fungus was hidden in the logs. So were European elm bark beetles (甲壳虫). These insects breed in dead and dying elms, but they feed on healthy trees. As the freight cars rolled toward Ohio, the hatching European beetles, carrying the fungus on their bodies, left the dead French logs for the bark of living American elms. Suddenly, American elms began dying. One year an American elm tree could be healthy. The next year it would turn yellow and wilt (枯萎). The following year it would be dead. By 1980, the fungus had killed as many as 77 million American elms. Towns and cities across America had lost their elm trees. Scientists like Denny Townsend of the National Arboretum (植物园) in Maryland and another research station in Delaware, Ohio, are trying to save the American elm from dying out. Townsend finds elms that have stayed healthy. Then he makes cuttings from the trees and grows them into new trees. He tests these saplings by injecting them with the fungus to see if they can survive. Townsend estimates that only 1 in 100,000 American elm trees can resist Dutch elm disease. By doing this, Townsend found two American elm strains, New Harmony and Valley Forge, that resist the disease. Their saplings, now growing in nurseries, will be big enough in just a few years to plant in streets and yards, maybe in your neighborhood, to replace the elms that stood there years ago.