Chronon seed

Professor Kalu claimed to have created the chronon seed, which she isolated in order to be able to measure interstitial time. After operating their chronon bomb, and being flung into the Time Vortex together, Chris Jennings was in possession of Kalu's chronon seed. He gave it to Tegan Jovanka to keep her and the Fifth Doctor from leaving in the TARDIS. (AUDIO: Interstitial)