Modern art is often accused of being ephemeral. Usually when people say this, what they really mean is "not much good". In the case of the Chinese artist Song Dong, however, the label is entirely appropriate. Dong's work is ephemeral in the word's literal sense: it doesn't last very long. And the reason for this is that it gets eaten - often within hours of going on show.
Dong has become famous in China for building miniature cities made entirely out of biscuits. They tend to be fantastical creations rather than depictions of actual places, although in style they resemble the imperial cities of ancient China. Dong has created four such sculptures in his native land, and one in France. Now he has constructed another, on the lower ground floor of Selfridges in central London.
Completed on Wednesday 22 February, Dong's latest work in his Eating the City project may already have been consumed by the time you read this. The precedents are not encouraging. The city Dong built two years ago in Xian, central China, lasted just two hours. More than a thousand people went to see it, and they devoured every crumb. Yet Dong seemed relatively upbeat about the chances of his new edible city surviving at least until the weekend. "People in China are very hungry. They want to eat as many biscuits as possible. In London it's different. People are not so hungry here."
Unlike his previous creations, Dong's latest work combines both modern and traditional idioms. On three large rectangular tables he has mapped out zones: a business district, an administrative quarter and an ancient city. When I visit, the development is taking shape.
Although the ancient quarter is well under way, the modern sections are still very much works-in-progress. A few solitary blocks rise up like Jenga towers from the table, the surface of which has been entirely covered in upside-down Ryvitas.
A tad disappointingly, the project is being sponsored by McVitie's, with the result that the biscuit selection is not hugely classy. I spot Digestives, HobNobs and Rich Tea, as well as several varieties of wafer, which seem especially handy for building skyscrapers. Dong, in fact, appears unimpressed with his materials. "Chinese biscuits are more colourful," he says. "Better for making prettier buildings."
It's all great fun - and tasty to boot - but what does it mean? Is Dong saying something serious, or simply wasting lots of biscuits (it's estimated he used 72,000)?
Understanding him isn't always easy - we communicate through a translator - but as we talk I begin to get a sense of the upheaval and loss that underpin his work. Dong, who is 40, grew up in a deprived neighbourhood of Beijing. Like many Chinese he has witnessed profound changes during his lifetime. In cities such as his country's capital countless buildings have been destroyed, only to be replaced by featureless tower blocks.
Dong's family moved away from the house he grew up in when he was a teenager. It no longer exists. "I was too young to own a camera, but I managed to draw a picture of our courtyard before we left," he says. "In China, so much of what people have exists only in memories, drawings or photographs."
And this, perhaps, is why Dong creates art whose only permanence is in the minds of those who see it. His biscuit cities, at once grandiose and childlike, are monuments to ways of life that have been vanquished, but not forgotten.
When I ask Dong why he uses biscuits to make his sculptures, he replies: "Because biscuits are sweet. They are delicious and desirable. But remember, things that are sweet can be dangerous if you eat too much. They are like beautiful poison."
Memory, like so much else in modern China, is both a good and a bad thing.