Dutch elm beetles spread a fungal disease known as Dutch elm disease. Native to Asia, the disease spread to the United States in the late 1920s. Elm trees react to the fungus through plugging their xylem tissue with gum and tyloses (extensions of the xylem cell wall), but this prevents nutrients and water being delivered to the rest of the plant and eventually kills it. Affected trees are identified by their shedding leaves in summer, and once symptoms are evident treatment is difficult. Grosse Pointe has around 700 elms, more than most areas affected by the disease probably because of local money available to support treatment and prevention. However, in 1951 there were about 4000 elms.