Plasticity in shoot development: a biophysical view.

The construction and spacing of leaves can be analysed in terms of the direction of reinforcement in the walls of the organ surface. In general, growth is at right angles to the reinforcement. When, however, tissues are actively stretched by adjacent organs they apparently take on, by cell activity, reinforcement which lies in the direction of stretch. Thus reinforcement can dictate extension direction; extension direction, when imposed on a tissue, may dictate reinforcement direction. This proposed two-way relationship has been used to model the activity of shoot meristems. It produces biophysically plausible schemes for the progressive development of various leaf structures and for the cyclical revision of apical structure seen in various types of phyllotaxis.