wheel. Hebrew. galgal, a rolling thing. Probably the wild artichoke, which throws out branches of equal length, and, when ripe and dry, breaks off at the root, and is carried by the wind, rolling like a wheel over the plains. Compare Isa_17:13; where it is again used with "chaff", and rendered "a rolling thing" (margin thistledown).
stubble = straw. Hebrew. kash = the dry haulm of grain, which is carried about by the wind like the galgal.