For a very long time, the United States of America was commonly referred to as a "melting pot." Recently, such a conceptualization has come under scrutiny because of the implication that everyone within the figurative "pot" must "melt" and assimilate into a homogeneous mass. As a substitute, then, the metaphor of the salad bowl has been suggested in order to imply, instead, that all parts of the mixture retain their shape, and do not melt in to homogeneity, but remain a heterogeneity. A newer metaphor still has been suggested, that of a mosaic, in order to highlight the integral nature of each piece and the sense of an overarching form.