Bill, With a stationary baler, there is a cut piece of wire with a loop on one end. The unlooped end is fed through slots in vertical blocks that separate the bales. When the wire comes through at the end of bale on the same side it was started, it is passed through the loop and twisted around the wire by hand. I'm not sure what the next version consisted of, but I would assume that when the baler was pulled through the field, the wire "knotting" and cutting would have been done by the machine.
Bob