Mechanical Stress and Cell Wall Orientation in Plants. I. Photoelastic Derivation of Principal Stresses. With a Discussion of the Concept of Axillarity and the Significance of the “Arcuate Shell Zone”

This study describes a further investigation into the meaning of patterns of cell wall orientation in plants and outlines a modified method for the generation of patterns of principal stresses in a two‐dimensional model. Evidence from simple photoelastic models is presented which supports the concept that the initial location of a presumptive axillary bud primordium may be controlled by mechanical stress in the region of the leaf axil.