In separate installations of the History Apparatus, the artist planted in each location a stump from a tree that had lived over a hundred years: on the central square of Neumarkt in the town of Arnsberg and on the terrace of the Neue Nationalgalerie in Berlin. The installation was placed on the unaltered existing ground. The cut-down tree exists only in the mind of the observer. The stump bears witness to a past that might have been.
Source:http://juliusvonbismarck.com/bank/index.php?/projects/history-apparatus/