If the undercooling is not very strong, then the interface degenerates to an approximately sinusoidal form and an array of cells is generated. When the undercooling is stronger (e.g. V>>Vcrit), then side branches form and a branched dendritic ("tree-like") structure develops.

When constitutional undercooling occurs, a planar growth front is unstable and tends to break down into more complex morphology.

Under these conditions, both the primary trunk and the secondary and higher order branches tend to grow in the easy growth directions, which are the <100> crystallographic directions for cubic metals. This is thought to occur because of dependence of the rate of addition of molecules onto the solid at an interface on the crystallographic orientation of the solid.
Explore the conditions under which a planar growth breaks down into more complex morphology.