Wood Grain Pattern Formation: A Brief Review

In trees, new wood develops from a layer of stem cells called the vascular cambium. A subpopulation of cambial cells—the fusiform initials—are elongated and capable of coordinated reorientation in response to internal and external stimuli. Changes in the orientation of fusiform initials in turn leads to changes in the grain pattern of developing wood. This article reviews the phenomenon of cambial orientation, with an emphasis on a recent computer model that takes the plant hormone auxin as the orienting signal. New model results are presented that demonstrate the surprisingly complex grain patterns that can emerge from simple initial conditions, in qualitative agreement with similar patterns found in wood. Lastly, an alternative theory of wood grain pattern that takes mechanical stress as the orienting signal is critically evaluated.