An Oak Tree consists of an ordinary glass of water placed on a small glass shelf of the type normally found in a bathroom, which is attached to the wall above head height. Craig-Martin composed a series of questions and answers to accompany the objects. In these, the artist claims that the glass of water has been transformed into an oak tree.... http://www.tate.org.uk/art/artworks/craig-martin-an-oak-tree-l02262
https://offthewalls.wordpress.com/2009/01/31/an-oak-tree-michael-craig-martin/