Celery

During his fifth incarnation, the Doctor took to wearing a stalk of celery on the left breast of his frock coat. This began after his regeneration when he visited the city of Castrovalva in Andromeda. He considered it as a sign of civilisation. (DW: Castrovalva) This incarnation claimed to be allergic to certain gases in the Praxis range of the spectrum, in the presence of which the herb turns purple. In that case, he would eat the celery. (DW: The Caves of Androzani) However this may be a lie, as the Tenth Doctor described it as merely a "decorative vegetable" when he met his fifth incarnation. (DW: Time Crash)


 * Whether this allergy may extend to all Gallifreyans, only some of them, or to all the Doctor's incarnations or only his fifth, is not known.

While attending dinner as a guest (or captive) of the Eternal Captain Striker, the Doctor replaced his old stalk with a fresh one (DW: Enlightenment). He also attempted to revive a dying Peri by having her smell it. Her human olfactory sense did not suffice for the plant to help her. (DW: The Caves of Androzani)

A later incarnation would later refer to his younger self's decision to wear celery stalks with some distain and mocking humour during an encounter between the two incarnations. (DW: Time Crash)