TARDIS coral

TARDIS coral is the organic substance of which a TARDIS is composed. The vessels are grown, not built. (DW: The Impossible Planet). The interior of the Ninth and Tenth Doctor's TARDIS have a coral-like appearance; lots of pillars seem more like trees or vines than structural support, and an unnamed coral like substance is visible on some parts of it.

However, when brielfy merged with his Tenth incarnation's TARDIS, the Fifth Doctor notes that the coral structures could be part of the current TARDIS desktop theme. He also adds that it is worse than the presently unseen "leopard skin" look (DW: Time Crash)

No other incarnation of the console room (except perhaps the tertiary console room in NA: Nightshade) has shown these organic characteristics.

TARDIS coral started growing around the tribophysical waveform macro-kinetic extrapolator after it was integrated with the TARDIS long enough.

In Torchwood 3, some TARDIS coral can be seen growing on Jack Harkness' desk, although this has not yet been fully explained.

Behind the Scenes
Part of the Bad Wolf Bay scene at the end of (DW: Journey's End) was removed in which the Doctor gave the Meta-Crisis Tenth Doctor and Rose a piece of TARDIS coral, and Donna told them how to increase the rate of growth by a factor of 59. (This scene was removed due to complicating Rose's departure, but it will be included in the DVD box set.)

According to the deleted scene a piece of TARDIS coral roughly the size of a mouse, would take thousands of years to grow a TARDIS.