Collectors: From Mondrian to Martial Airs

For nearly everyone, a mania for collecting is a transitory phase of childhood. But for a few, the habit becomes a lifelong obsession. For Manhattan Art Dealer Sidney Janis, it began with hoarding marbles during his boyhood in Buffalo, and led to a perceptive collection of 20th century art. For Anne Kinsolving Brown, daughter of a Baltimore minister, the impetus came from a book on soldiers that she spied in a toy store at the age of nine. "The bands were still playing in 1915," she recalls, "and the French poilu still...