Serial: 4L  Episode Nos. 422, 423, 424, 425, 426, and 427.  Title: The Seeds of Doom

An expedition in Antarctica uncovers two gourd-like seed pods.  When one germinates, it infects a man and begins turning him into one of it's own kind: a plant monster known as a Krynoid that seeks to consume all animal life.  The Doctor and Sarah try to help, but their efforts are frustrated by agents of a wealthy, obsessive botanist who steal the second pod and take it to him in England.  Will the Doctor be able to prevent the cultivation of the Krynoids, or is the world truly doomed by their seeds?

starring Tom Baker as Doctor Who and Elisabeth Sladen as Sarah Jane Smith. Written by Robert Banks Stewart, Produced by Philip Hinchcliffe, and Directed by Douglas Camfield.

Originally transmitted from 31 January 1976 to 6 March 1976 on BBC1.