Eocian grass
From Tardis Wiki, the free Doctor Who reference
Eocian grass, also known as blue grass, was a species of sentient blue grass found on Gallifrey.
Eocian grass would attack passersby when it was feeling threatened, and was generally difficult to traverse for this reason.
It could also be distilled into a metampsychosis compound, which acted as an elixir to make Time Lords immortal, by allowing them to remain alive while avoiding regeneration, renewing them physically in the process. According to the Fourth Doctor, "it puts an old shoal into a new body". The effect was exponential, requiring repeated baths to attain "reverse metamorphosis" into their incarnation's strongest form. (AUDIO: Metamorphosis [+]Loading...["Metamorphosis (audio story)"])
