Computational wood? Is it possible to grow electronic circuits inside living trees? Matt Cottam thinks so. In his master's thesis, he created a video describing a technique for injecting trace metals to create elaborate living circuits.
(Grow circuits in living trees)
As far as I can tell, this video does not describe prototypes, but is a design concept. Still, it's a pretty cool idea - particularly in terms of implementation - and one that has already been described in science fiction.
In his award-winning 1989 novel Hyperion, Dan Simmons describes titanic treeships that are grown to move between the stars:
The Consul remembered his first glimpse of the kilometer-long treeship as he closed for rendezvous, the treeship's details blurred by the redundant machine and erg-generated containment fields which surrounded it like a spherical mist, but its leafy bulk clearly ablaze with thousands of lights which shone softly through leaves and thin-walled environment pods, or along countless platforms, bridges command decks, stairways and bowers. Around the base of the treeship, engineering and cargo spheres clustered like oversized galls while blue and violet streamers trailed behind like ten kilometer-long roots...
(Read more about treeships)
More recently, the idea of trees that conduct information is explored in the blockbuster movie Avatar:
Seabreacher, H.G. Winter's 1939 Torpoon
'Ken lay full-length in the padded body compartment, his feet resting on the controlling bars of the directional planes, hands on the torpoon's engine levers.' - HG Winters, 1939.