Dr who fifth doctor quotes The Caves of Androzani

The Doctor: Androzani Major was becoming quite developed last time I passed this way.

Peri: When was that?

The Doctor: ...I don't remember. I'm pretty sure it wasn't the future.

Peri: Doctor, why do you wear a stick of celery in your lapel?

The Doctor: Does it offend you?

Peri: No, just curious.

The Doctor: Safety precaution. I'm allergic to certain gases in the praxis range of the spectrum.

Peri: Well, how does the celery help?

The Doctor: If the gas is present, the celery turns purple.

Peri: And then what do you do?

The Doctor: I eat the celery. If nothing else, I'm sure it's good for my teeth.

The Doctor: Adric?