The pod plant was a lifeform discovered on planet Omicron Ceti III by botanist Leila Kalomi. The plant served as a repository for the Omicron spore, and squirted them out of its flower at anyone uninfected who came too close.
When the inhabitants of Omicron colony tried to infect the crew of the USS Enterprise with the spores, an infected Doctor Leonard McCoy had numerous pod plants beamed up to the ship, where the spores quickly spread through the ventilation system. Determined to escape the planet, Kirk found out that anger helps the victim fight off the spores. (TOS: "This Side of Paradise")