Ma Joad in The Grapes of Wrath, Mammy in Gone with the Wind, Auntie Em in The Wizard of Oz --all were unforgettable characters who played an integral part in some of Hollywood's most memorable productions. For over three decades, from the 1930s to the 1950s, character actresses who brought such roles to life were one of Hollywood's great but little acknowledged assets. Often lured from Broadway yet billed fifth or sixth...