Fig. 3 Site of auxin maximum initiates morphogenesis. (a) The
auxin patterning process leads to a local area of auxin accumulation.
(b) Auxin can induce expansin (EXP) gene expression which promotes
cell growth. Due to the biophysical pattern of stress and tension in the
SAM, local increased growth is liable to occur in a radial direction,
leading to tissue bulging out of the SAM.