Genesis 30:37-38 ▼

37 And Jacob takes to himself a rod of fresh poplar and almond and plane-tree, and peels in them white peelings, making bare the white that [is] on the rods,

38 and sets up the rods which he has peeled in the gutters in the watering troughs (where the flock comes to drink), in front of the flock, that they may conceive in their coming to drink;