Citrus grows in citrus fields south of Huaihe River and Hovenia dulcis Thunb. north of Huaihe River. Metaphor means that the same species varies due to different environmental conditions.
Original: Yan Zizhi, the king of Chu, gave Yanzi wine, and the wine was full. Two officials tied a man to the king. The king said, "What about those who are bound?" He said, "Qi people are also thieves." The King of Qi looked at Yan Zi and said, "Are Qi people good at stealing?" Yan Zi avoided the table and said, "Babies smell it, but oranges are born in Huainan and oranges are born in Huaibei. Leaves are similar to disciples, but they taste different. What's that? Soil and water are different. Now people's livelihood is better than Qi's, but they stole it when they went to Chu. If he has soil and water without Chu, then the people are good and thieves. " Wang smiled and said, "saints are not interested in happiness, but I am interested in disease."
When the king of Chu laughed at Qi people for stealing, Yan Zi stood up and said, "Why didn't your majesty know?" Citrus in Huainan is big and sweet. And a citrus species in Huaibei can only produce small and bitter oranges. Isn't it because the water and soil are different? By the same token, the people of Qi lived and worked in peace and contentment in Qi, and became thieves in Chu. Maybe the water and soil in the two countries are different. "This passage contains an idiom: southern oranges and northern oranges. Fructus Aurantii: Deciduous shrub, bitter and sour, spherical. Also called orange. Oranges in the south will become bitter oranges when transplanted to the north of Huaihe River. Metaphor means that the same species varies due to different environmental conditions. )