The magnetic energy stored in the corona is the only plausible source for the energy released during huge solar flares. However, this stored magnetic energy cannot be released efficiently unless rapid magnetic reconnection occurs. The strongest evidence for reconnection comes from observations of the chrornospheric ribbons and the coronal loops which form afier fhe onset of the
flare. The ribbons and loops appear to propagate through the chromosphere and corona during the flare, but Doppler-shift measurements show conclusively that these apparent rnotions are not due to mass motions of the solar plasma. The motions can only be explained by the upward propagation of an energy source in the corona, and in th MHD-reconnection model of flares, the propagating energy source is an x-iine accompanied by slow-mode shocks. The upward motion of the x-line occurs because the enormous inertia of the photosphere immobilizes the photospheric footpoints oř the field lines which reconnect at the x-line.