Why tumbleweeds tumble

Recently, Carla posted about tumbleweeds invading Victorville, California leading to numerous 911 calls. Why do tumbleweeds tumble though? To make more tumbleweeds of course. From KQED's Deep Look:

Starting in late fall, (tumblweeds) dry out and die, their seeds nestled between prickly dried leaves. Gusts of wind easily break dead tumbleweeds from their roots. A microscopic layer of cells at the base of the plant called the abscission layer makes a clean break possible and the plants roll away, spreading their seeds. When the rains come, an embryo coiled up inside each seed sprouts.