Ep 22. The Flaming Planet

Violating orders, Doctor Smith has grown an alien plant in his cabin. Space radiation turns it into a monstrous mutant that thinks he's its "mother!" Ordered to dispose of it into the jets, Smith instead lazily flushes it out an airlock, and it promptly attaches to the ship, causing engine problems! To remove the plant, John proposes a close passage through the dense atmosphere of a nearby planet - but that planet is inhabited, and the residents do not want visitors. The Jupiter 2 lands anyway, and then discovers that the planetary inhabitants demand a high price for their safe departure!