Master Plant

The Master Plant was an intelligent plant created by Professor Rayner, capable of controlling other forms of plant life. Rayner hoped to use it in his plans to rule, but after feeding it more of his potion, it turned on him and killed him, no longer needing him. It grew to huge size and pursued the Third Doctor, Dave Lester and Carradine to a laboratory, where it took control of the local plants and made them attack the building. With Dave's assistance, the Doctor made a weed-killer out of chemicals in the lab and sprayed the plant with it, killing it. Upon its death, the other plants returned to normal