In the winter of 1636, Dutch traders were buying and selling tulip bulbs that were still in the ground: paper promises on flowers nobody had seen. The rarest bulbs changed hands for more than a craftsman earned in a decade. In February 1637 the bids stopped, and a tulip went back to being worth a tulip.
Ever since, "tulip" has been the word people reach for whenever the financial system goes nuts. Jan Brueghel the Younger shown it first - painting the speculators as monkeys in merchant dress: one poring over a price list, a table heaped with coins, flowers trampled into the dirt.