cardamom, and ginger, as well as oysters with wine, fried squid with ginger and vinegar, horseshoe crabs and red crabs, shrimp, and pufferfish, which the Chinese called 'river piglet'. Some foods were also off-limits, as the Tang court encouraged people not to eat beef (since the bull was a valuable draft animal), and from 831 to 833 Emperor Wenzong of Tang banned the slaughter of cattle on the grounds of his religious convictions to Buddhism. From the trade overseas and over land, the Chinese acquired golden peaches from Samarkand, date palms, pistachios, and figs from Persia, pine seeds and ginseng roots from Korea, and mangoes from Southeast Asia. In China, there was a great demand for sugar; during the reign of Harsha (r. 606–647) over North India, Indian envoys to Tang China brought two makers of sugar who successfully taught the Chinese how to cultivate sugarcane. Cotton also came from India as a finished product from Bengal, although it was during the Tang that the Chinese began to grow and process cotton, and by the Yuan Dynasty it became the prime textile fabric in China. During the earlier Southern and Northern Dynasties (420–589), and perhaps even earlier, the drinking of tea became popular in southern China. (Tea comes from the leaf buds of Camellia sinensis, native to southwestern China.) Tea was viewed then as a beverage of tasteful pleasure and with pharmacological purpose as well. During the Tang Dynasty, tea became synonymous with everything sophisticated in society. The Tang poet Lu Tong (790–835) devoted most of his poetry to his love of tea. The 8th-century author Lu Yu (known as the Sage of Tea) even wrote a treatise on the art of drinking tea, called the Classic of Tea (Chájīng). Tea was also enjoyed by Uyghur Turks; when riding into town, the first places they visited were the tea shops. Although wrapping paper had been used in China since the 2nd century BC, during the Tang Dynasty the Chinese were using wrapping paper as folded and sewn square bags to hold and preserve the flavor of tea leaves. Methods of food preservation continued to develop. The common people used simple methods of preservation, such as digging deep ditches and trenches, brining, and salting their foods. The emperor had large ice pits located in the parks in and around Chang'an for preserving food, while the wealthy and elite had their own