Leaf stem node. Light micrograph of a vertical section through a leaf stem node from a sycamore tree (Acer pseudoplatanus). The node (centre) has two leaf stems (petioles) branching off at upper left and right. This image shows the formation of cork (phellogen layer, red), and the abscission layer (green) that forms at the base of the petioles prior to the leaves falling from the plant in the autumn.