Regular trade began in Canton (now Guangzhou), where it was controlled by two monopolies: the Chinese "Cohong" (trading companies) and the British East India Company. The "Cohong" acquired tea from 'tea men' who had an elaborate supply chain into the mountains and provinces where tea grew. The East India Company brought back many products, of which tea was just one, which proved one of the most successful. It was initially promoted as a medicinal beverage or tonic but by the end of the 17th century was taken as an all-purpose drink, albeit mainly by the elite, as it was expensive. Tea was traded in significant amounts by the 18th century, when tea was being sold by grocers and tea shops in London. By the 1720s black tea overtook green tea in popularity as the price dropped, and early on British drinkers began adding sugar and milk to tea, a practice that was not done in China. By the 1720s European maritime trade with China was dominated by exchange of silver for tea. As prices continued to drop, tea became increasingly popular and by 1750 had become the British national drink. A fungus reduced coffee production in Ceylon by 95% in the 19th century, cementing tea's popularity. The escalation of tea importation and sales over the period 1690 to 1750 is mirrored closely by the increase in importation and sales of cane sugar: the British were not drinking just tea but "sweet" tea. Thus, two of Britain's trading triangles converged: the sugar sourced from Britain's trading triangle encompassing Britain, Africa and the West Indies and the tea from the triangle encompassing Britain, India and China.