The general structure of the stem is essentially a mirror of the root, with apical meristem at the tip, the three primary meristems just behind the apical meristem and the three ground tissues and more mature structures down lower, behind the three primary meristems. The axillary buds are located in the leaf axils. Spring wood is formed early in the year, and has large lumens.
Summer wood is formed later, and has small lumens.
Thus, the initiation of springwood growth in the growing season creates a very visible delineation between the years' growth. It is generally lighter in color than heartwood. 1. rhizome - underground stem. 2. tuber - underground storage stem. 1. simple - single blade 2.