Differentiation, Organogenesis, and the Tectonics of Cell Wall Orientation. Iii. Theoretical Considerations of Cell Wall Mechanics

This paper is concerned with the relationship between cell wall orientation in dividing tissues and stress. An examination of the possible orientations of a cell‐plate in a cell under axial stress reveals that only one orientation passing through the center of the cell can be completely free from shear stress, thus providing a favored plane for the positioning of an hypothetical, shear‐sensitive, cell‐plate precursor. From this principle of shear‐free partitioning, and the three basic rules of stress behavior along free boundaries, it is possible to predict certain features of cell wall orientation along free edges and epidermal surfaces and in some simple apices. The possible significance of the widespread phenomenon of axillary induction of bud formation is discussed in terms of the generation of stresses at the base of the axillant leaf, and the general efficacy of mechanical stress as a spontaneously arising morphogenetic trigger is considered.