Jamieson, Fausset and Brown on Genesis 30:37

37. Jacob took rods, &c.--There are many varieties of the hazel, some of which are more erect than the common hazel, and it was probably one of these varieties Jacob employed. The styles are of a bright red color, when peeled; and along with them he took wands of other shrubs, which, when stripped of the bark, had white streaks. These, kept constantly before the eyes of the female at the time of gestation, his observation had taught him would have an influence, through the imagination, on the future offspring.