Cell wall thicknesses of hypocotyls freeze-fractured at their mid-points at the developmental stages described in Fig. 1 (A, light-; B, light+GA-; C, dark-grown hypocotyls). Mean thicknesses are given ±SE (n=23) pooled from five hypocotyls for each treatment and developmental stage. Walls in outer epidermis (OE), inner epidermis (IE), outer cortex (OC), inner cortex (IC), and endodermis (EN) were measured.