  Structural aspects of crystal nucleation in undercooled liquids are explored
using a nonlinear hydrodynamic theory of crystallization proposed recently [G.
I. Toth et al., J. Phys.: Condens. Matter 26, 055001 (2014)], which is based on
combining fluctuating hydrodynamics with the phase-field crystal theory. We
show that in this hydrodynamic approach not only homogeneous and heterogeneous
nucleation processes are accessible, but also growth front nucleation, which
leads to the formation of new (differently oriented) grains at the solid-liquid
front in highly undercooled systems. Formation of dislocations at the
solid-liquid interface and interference of density waves ahead of the
crystallization front are responsible for the appearance of the new
orientations at the growth front that lead to spherulite-like nanostructures.
