When solids with complicated forms are seen, it has usually been assumed that they must be aggregates of many separate crystals, with each crystal having a simple faceted shape. But the results given here indicate that in fact individual crystals can yield highly complex shapes. There will nevertheless be cases however where multiple crystals are involved. These can be modelled by having a cellular automaton in which one starts from several separated seeds. Sometimes the regions associated with different seeds may have different characteristics; the boundaries between these regions then form a Voronoi diagram (see page 1038).