How (and why) does a Gamma match work, when used on the driven element of a Yagi antenna? As shown here:

(source: http://www.iw5edi.com/ham-radio/?2-element-yagi-for-10-meters-band,49)

The article describes a 10 meter Yagi where the driven element is one continuous conductor and not the classic dipole-halves driven by 50 ohm coax. I have seen other designs where Gamma matches were used on split folded dipole elements joined on the far end. Clearly capacitance is the key, but I don't understand how it can work efficiently.