Fig. 11.3-1. Transverse section of parsnip stem (Pastinaca sativa). The cortex of the stem is often simply a thin layer of parenchyma only 5 to 10 cells thick, with almost nothing distinctive about it. The cortex of this parsnip has prominent bands of collenchyma and secretory ducts. The outermost layers of cortex are an aerenchymatous hypodermis (just above the label “Collenchyma”).