Celery

During his fifth incarnation, the Doctor took to wearing a stalk of celry on the right breast of his frock coat. This began after his regeneration when he visited the city of Castrovalva in Andromeda (DW:Castrovalva).

This incarnation claimed to be allergic to certain gases in the Praxis range of the spectrum, in whose presence the herb turns purple.In that case, he would eat the celery. (DW:The Caves of Androzani''


 *  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")