used as eating utensils. They began to take on this role during the Han dynasty, but it was not until the Ming that they became ubiquitous for both serving and eating. It was not until the Ming that they acquired their present name (, kuaizi) and their present shape. The wok may also have been introduced during the Han, but again its initial use was limited (to drying grains) and its present use (to stir-fry, as well as boiling, steaming, roasting, and deep-frying) did not develop until the Ming. The Ming also saw the adoption of new plants from the New World, such as maize, peanuts, and tobacco. Wilkinson remarks that to "somebody brought up on late twentieth century Chinese cuisine, Ming food would probably still seem familiar, but anything further back, especially pre-Tang would probably be difficult to recognize as 'Chinese'". The "Silk Road" is the conventional term for the routes through Central Asia linking the Iranian plateau with western China; along this trade route passed exotic foodstuffs that greatly enlarged the potential for Chinese cuisines, only some of which preserve their foreign origin in the radical for "foreign" that remains in their name. "It would surprise many Chinese cooks to know that some of their basic ingredients were originally foreign imports," Frances Wood observes. "Sesame, peas, onions, coriander from Bactria, and cucumber were all introduced into China from the West during the Han dynasty". Classifications Not long after the expansion of the Chinese Empire during the Qin dynasty, Han writers noted the great differences in culinary practices among the different parts of their realm. These differences followed to a great extent the varying climates and availabilities of foodstuffs in China. Many writers tried their hands at classification, but since internal political boundaries over the centuries did not coincide with shifting cultural identities, there was no way to establish clear-cut or enduring classifications or ranking of foods and cooking styles. Different ethnic groups might occupy only small areas, but their cuisines were included in systematic lists from early on. Certain broad categorizations are useful, however: Northern and southern cuisine The primary and earliest distinction was between the earlier settled and relatively arid North China Plain and the rainier hill country south of the Yangtze River which were incorporated into the Chinese empire much later. First canals and now railroads and highways have blurred the distinction, but it remains true