“Tree Listening,” by Alex Metcalf, amplifies the sound of water moving up through a tree (is that actually possible?) and plays it through headphones hanging from said tree. Says the artist:

While listening to the headphones hanging from the trees branches you can hear water being pulled up from the roots to the leaves through the xylem tubes. You will hear a quiet popping sound that is produced by the water passing through the cells of the xylem tubes and cavitating as it mixes with air on its’ way upwards. In the background is a deep rumbling sound that is produced by the tree moving vibrating. As the leaves lose the water through evaporation the cells below the leaf become drier and they in turn pull water from the next cells below, this carries on down the tree all the way down to the roots. The water molecules cling together and form a water chain from the leaves to the roots under tension-cohesion.

In spite of my doubts about what is actually going on sonically, it looks pretty neat!