Cheng also has a way.That is using tree glue.As for where tree sap comes fromLook around, you now have a grove of weeping willows!Willow trees are an important species for producing tree sap. It's il...there were supply lines available within the country, General Meng Tian still chose to cultivate land in the Hexi Corridor.... and even famous general Huo Qubing didn't rely entirely on the rear.The...