"straw boss"

Can anyone identify the origin of the phrase "straw boss"? I have been able to find its meaning but not the origin. Thank you

From Wentworth & Flexner, Dictionary of American Slang, 1960 edition:

"'Origin of term: the boss attended to the grain going into the thresher; the second-man watched after the straw coming out and hence had little to do.' H. F. Barker. Colloq. since c1900; orig. hobo use."