He bought a drawing every two to three years, sometimes donating to the small collection of the National Gallery of Art in Washington.

Stone first came to China in 1982, to teach as a visiting scholar at Beijing's Capital Normal University. He returned regularly, lecturing at universities and academic institutions nationwide.

"In America every major university has an art museum. Princeton has a permanent collection of works of masters such as Van Gogh, Monet and Renoir. It is free. Students can just come over to see these beautiful pieces and then go back to their studies," Stone says.

In China, he laments, "it is not common".

Stone's collection not only delights the students at PKU. It has toured Macao and Urumqi, the Xinjiang Uygur autonomous region, where hundreds of people lined up in snow to see their first Picasso work.

Stone's generosity has sometimes yielded surprises.

He once bought one of six Matisse prints at a Paris art store. He told the Jewish owner, Ann Pfeffer, that his purchase would go to the Sackler museum in China. Later he opened the package, he found Pfeffer had given him all six for the price of one, $3,500.

Back at the store, the dealer told him that she had made no mistake: She was giving the other five as gifts to China, because China was one of very few countries that welcomed Jewish refugees during World War II.

Last year, Stone won the Chinese Government Friendship Award, the country's top award to foreign experts for making contributions in different fields.

"I love being here. I taught at Harvard, New York University and City University of New York. I speak of my life as 'BC' and 'AC' - before China and after China," he says.

Stone says the favorite of his collection is a painting of Liu Yongming, a pupil of ink-and-color master Wu Guanzhong.

After discovering Liu in 1991 at an exhibition at the National Museum of China, Stone asked the artist to paint magpies, a common bird he saw in Beijing.

"I have drawings and prints scattered all over in my apartment in New York. But that painting is what I first see in the morning when I get out of bed, and the last thing I see before I turn off the light.

"It is in my bedroom. It was painted by an artist I love, of subjects I love, and it is a gift to me."