As the flowers grew in popularity, professional growers paid higher and higher prices for bulbs with the virus, and prices rose steadily. By 1634, in part as a result of demand from the French, speculators began to enter the market. The contract price of rare bulbs continued to rise throughout 1636, but by November, the price of common, "unbroken" bulbs also began to increase, so that soon any tulip bulb could fetch hundreds of guilders. That year the Dutch created a type of formal futures market where contracts to buy bulbs at the end of the season were bought and sold. Traders met in "colleges" at taverns and buyers were required to pay a 2.5% "wine money" fee, up to a maximum of three guilders per trade. Neither party paid an initial margin, nor a mark-to-market margin, and all contracts were with the individual counter-parties rather than with the Exchange. The Dutch described tulip contract trading as "windhandel" (literally "wind trade"), because no bulbs were actually changing hands. The entire business was accomplished on the margins of Dutch economic life, not in the Exchange itself.