When the Metropolitan Museum opens its new Lila Acheson Wallace Wing for 20th century art next week, New York City's role as the world's main showplace for modern painting and sculpture may fairly be said to have reached its saturation point. After the Museum of Modern Art, the Guggenheim Museum and the Whitney Museum, this is the fourth major institution on the island of Manhattan given over to collecting, showing, classifying and presenting ideas about the art of this century -- not counting the hundreds of commercial galleries and dozens of "alternative spaces" with which the city is studded.
If there...