Mow down : v.tr. "Mowing" is cutting with a scythe or a mower. Mow cereals, wheat.
Steal. I was robbed of my wallet.
We caught it to mow in the stores.
By extension, take: He has robbed her of her place.
Broke like the wheat: without money.
The expression "Broke (like wheat)": very poor, ruined.
Broke, originally past participle of the verb mow, is a simple metaphor which assimilates the state of the purse of the totally destitute person (there is nothing left) to that of the completely mown field (nothing remains).
According to Gaston Esnault, it dates from 1877.
As for its extension with like wheat, it would have appeared in 1899. If this comparison goes without saying, we must also see a certain malice, since in slang the wheat denotes money.
And if the metaphor seems obvious, we can still note that in the XNUMXth century, at a time when people still walked around with hard cash in purses hung from their belts, the thief "mowed" when he cut. the purse and won.
Here we find a link with two of the slang meanings of broke since the one whose purse has been mown (stolen) is penniless (he is therefore broke).