1. In the presence of 2 % sucrose the curve representing the effect of the concentration of indoleacetic acid on the growth in length of etiolated pea stem sections of the variety “Rondo” shows two maxima separated by a depression. 2. The depression in the curve of longitudinal growth coincides with the optimum for lateral growth. 3. It is concluded that high lateral growth inhibits growth in length. 4. It is suggested that, when auxin activity in the cell is low, the cell wall is weakened mainly in longitudinal direction and that at higher auxin activities the cell wall is weakened in all directions.