  The existence of a clumpy, large-scale filamentary structure is at the basis
of the current paradigm of cosmic formation and evolution of clusters. The
star-formation history of galaxies falling into a cluster is altered as a
result of the environmental stresses. We investigate the relation between
substructure and properties of the galaxy population in a 30'x30' region
centered on the massive merging cluster A2744 at z~0.3. Multi-object
spectroscopy at low resolution and BVR photometry are used to detect the
presence of substructure through a Dressler-Schectman analysis and the
photometric redshift technique, respectively. Galaxies at the same photometric
redshift of the cluster are divided into red and blue according to their
distribution in the B-R vs. R colour-magnitude diagram. We identify two
large-scale filaments associated with A2744. Along these filaments, the
blue-to-red galaxy number ratio increases together with the cluster-centric
distance but peaks slightly beyond the cluster virial radius. The filaments
host a population of bright, large (i.e. more luminous than R* for the main
body of the cluster and with angular sizes of 13-22 $h_{70}^{-1}$ kpc) blue
galaxies that is hardly found among galaxies lying in a neighbouring
low-density environment at the same redshift of the cluster. These results can
be interpreted as a manifestation of galaxy harassment.
