Sap
From Tardis Wiki, the free Doctor Who reference
The sap from the Arkellis flower was used to infuse some Dalek casings. The first Dalek Emperor was enhanced with Arkellis sap. (COMIC: Genesis of Evil) Dalek Sec of the Cult of Skaro was also enhanced with Arkellis sap; by that time, the flower had become extinct. (PROSE: Birth of a Legend)