Growing System is always determined by many factors such as environment and physiological characteristics of the crops.In the competition with traditional crops,corn,from the beginning of its emergence in China,showed the advantages in mountainous area and replaced millets due to its high yield.In North China,corn yields one crop a year(the seedtime is in spring) or three crops per two years(the seedtime is in summer) while in South,China,corn is rotated with some other crops.During the past 300 years,the population of China increased tremendously.And the increasing population,along with the distribution of corn,moved from plain to mountainous area,from Central China to peripheral area.In the first half of the Qing Dynasty(1644-1911),corn was planted to the south of the Great Wall(built during the Ming Dynasty,1368-1644),and to the east of the Qinghai-Tibet Plateau.While in the late Qing Dynasty and the Republic of China(1912-1949),accompanied with the emigration into Northeast and Northwest China,corn distribution broke the original limit and extended to Northeast China,Qinling and Daba Mountains and Southeast China.In the concentrated distribution zone,corn played different roles in different areas.In the one crop a year spring corn rotated area of Northeast China,corn constituted the highest percentage of the crops.To the mid-20th century,corn accounted for 20% of the crops in Northeast China and became one of the dominant crops in this region.