Charles Ellicott Commentary Genesis 49:22

"Joseph is a fruitful bough, A fruitful bough by a fountain; His branches run over the wall." — Genesis 49:22 (ASV)

A fruitful bough. —Literally the words are, “Son of a fruitful tree is Joseph; son of a fruitful tree by a fountain: the daughters spread over the wall.” That is, Joseph is like a fruitful tree planted near a fountain of living water, and its branches, or suckers, springing from it, overtop the wall built around the spring for its protection. This fruitfulness of Joseph was shown by the vast number of his descendants.