The turban plant; Persian, thoulyb (thoulyban, a turban), by which name the flower is called in Persia. My tulip. A term of endearment to animals, as “Gee up, my tulip!” or “Kim up, my tulip!” Perhaps a pun suggested by the word tool. A donkey is a costermonger's tool.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894