Standing in front of a few dozen elementary and middle school runners piled into an auxiliary building at Caribou High School last Saturday, John Plourde told stories about perseverance and being humble. In each tale, the central figure was his father. Nearly 90 years ago, Emery Plourde was one of Maine’s brightest distance running stars. He helped Caribou to a team cross country title in 1938, set more than half a dozen state and county records…