  We present a computer simulation study on crystal nucleation and growth in
supersaturated suspensions of mono-disperse hard spheres induced by a
triangular lattice substrate. The main result is that compressed substrates are
wet by the crystalline phase (the crystalline phase directly appears without
any induction time), while for stretched substrates we observe heterogeneous
nucleation. The shapes of the nucleated crystallites fluctuate strongly. In the
case of homogeneous nucleation amorphous precursors have been observed (Phys.
Rev. Lett. {\bf 105}(2):025701 (2010)). For heterogeneous nucleation we do not
find such precursors. The fluid is directly transformed into highly ordered
crystallites.
