Grains in f.c.c. polycrystals that accommodate imposed deformation purely by slip processes develop a multi-scale dislocation substructure that evolves with deformation. When the polycrystal is subjected to rolling deformation or to channel-die compression, one of the elements of this substructure, called cell block boundaries, are widely reported to align parallel to the transverse direction and close to the macroscopic plane of maximum shear. This observation is explained based on standard rate-independent crystal plasticity augmented by three hypotheses. © (2012) Trans Tech Publications, Switzerland.