The Seeds of Doom
(1976): Two alien seed pods are found buried in the Antarctic permafrost. The Fourth Doctor, accompanied by Sarah-Jane Smith, realises that they are from a Krynoid, a form of voracious plant life that infects and transforms all animal life on planets upon which it becomes established. One of the pods opens and infects a scientist at an Antarctic base but the developing Krynoid is destroyed by a bomb set to cover the tracks of two men, Scorby and Keeler, who have made off with the other pod for their boss, eccentric plant collector Harrison Chase. The second pod infects Keeler and he also becomes a Krynoid, rapidly growing to giant proportions. UNIT are called in, and they arrange for the Krynoid to be bombed before it can spread its pods across the Earth.