  We report a detailed examination of the fine structure inside flare ribbons
and the temporal evolution of this fine structure during the X2.5 solar flare
that occurred on 2004 November 10. We examine elementary bursts of the C IV
(1550{\AA}) emission lines seen as local transient brightenings inside the
flare ribbons in the ultraviolet (1600{\AA}) images taken with Transition
Region and Coronal Explorer, and we call them C IV kernels. This flare was also
observed in Ha with the Sartorius 18 cm Refractor telescope at Kwasan
observatory, Kyoto University, and in hard X-rays (HXR) with Reuven Ramaty High
Energy Solar Spectroscopic Imager. Many C IV kernels, whose sizes were
comparable to or less than 2", were found to brighten successively during the
evolution of the flare ribbon. The majority of them were well correlated with
the Ha kernels in both space and time, while some of them were associated with
the HXR emission. These kernels were thought to be caused by the precipitation
of nonthermal particles at the footpoints of the reconnecting flare loops. The
time profiles of the C IV kernels showed intermittent bursts, whose peak
intensity, duration, and time interval were well described by power-law
distribution functions. This result is interpreted as evidence for
"self-organized criticality" in avalanching behavior in a single flare event,
or for fractal current sheets in the impulsive reconnection region.
