C. F. Keil and Franz Delitzsch on Genesis 49:22

Gen 49:22

“Son of a fruit-tree is Joseph, son of a fruit-tree at the well, daughters run over the wall.” Joseph is compared to the branch of a fruit-tree planted by a well (Psa 1:3), which sends it shoots over the wall, and by which, according to Ps 80, we are probably to understand a vine. בּן an unusual form of the construct state for בּן, and פּרת equivalent to פּריּה with the old feminine termination ath, like זמרת, Exo 15:2. - בּנות are the twigs and branches, formed by the young fruit-tree. The singular צעדה is to be regarded as distributive, describing poetically the moving forward, i.e., the rising up of the different branches above the wall (Ges. §146, 4). עלי, a poetical form, as in Gen 49:17.