“There is no science of race assimilation. No nation has had a sufficiently free opportunity with many diverse races to establish its enduring principles and certain procedure. America has this opportunity in her thirty-five different races speaking fifty-four languages, of whom 13,000,000 are foreign-born. One third of her total population has its roots in other soils and in diverse cultures. She has the laboratory for the experiment in her wide expanse of territory, much of it still unsettled; in the elasticity of her institutions ; and in the still formative state of her cultural life.”