Watermelon doesn't grow on trees, but in panicum miliaceum. Plants can't be grafted. In agricultural production, trees or shrubs are usually grafted between the same plant or the same plant. Because trees and shrubs can successfully find cambium, xylem and phloem. When grafting, it is necessary to ensure that the cambium between the scion and the rootstock is in contact with each other, so that with the cell division, the cambium cells on both sides will grow together and survive easily.