  Results of a systematic study of substructure in X-ray surface brightness
distributions of a combined sample of 470 REFLEX+BCS clusters of galaxies are
presented. The fully automized morphology analysis is based on data of the 3rd
processing of the ROSAT All-Sky survey (RASS-3). After correction for several
systematic effects, $52\pm 7$ percent of the REFLEX+BCS clusters are found to
be substructured in metric apertures of 1 Mpc radius ($H_0= 50 {\rm km} {\rm
s}^{-1} {\rm Mpc}^{-1}$). Future simulations will show statistically which mass
spectrum of major and minor mergers contributes to this number. Another
important result is the discovery of a substructure-density relation, analogous
to the morphology-density relation for galaxies. Here, clusters with asymmetric
or multi-modal X-ray surface brightness distributions are located
preferentially in regions with higher cluster number densities. The
substructure analyses techniques are used to compare the X-ray morphology of 53
clusters with radio halos and relics, and 22 cooling flow clusters with the
REFLEX+BCS reference sample. After careful equalization of the different
`sensitivities' of the subsamples to substructure detection it is found that
the halo and relic sample tends to show more often multi-modal and elongated
X-ray surface brightness distributions compared to the REFLEX+BCS reference
sample. The cooling flow clusters show more often circular symmetric and
unimodal distributions compared to the REFLEX+BCS and the halo/relic reference
samples. Both findings further support the idea that radio halos and relics are
triggered by merger events, and that pre-existing cooling flows might be
disrupted by recent major mergers.
