The yield on the 10-year benchmark German bund fell into negative territory for the first time ever on Tuesday morning, amid global growth concerns and jitters over the U.K.'s upcoming referendum on its European Union membership. At around 8.30 a.m. London time, the yield hit zero and briefly fell into negative territory as investors continued to flock to safe-haven assets. Bond prices and yields move in opposite directions and a negative yield implies that investors are effectively paying the German government for the privilege of parking their cash. By the end of the European trading day, the yield was still...