Plant growth by means of apical meristem leads to the development of sets of primary tissues: epidermis, cortex, vascular bundles, pith, and leaves. In addition to those primary tissues, tree species produce the secondary tissue “wood” from the vascular cambium. This secondary

growth is a highly ordered developmental process, which involves the patterned division of vascular cambium cells and a subsequent regulated differentiation of cambial derivatives into secondary xylem and phloem tissues. Its product, wood, serves as a primary feedstock for bioenergy, fiber, timber, and various natural compounds. Recently, wood is gaining popularity as a source of fermentable sugars for liquid fuel production. Thus, students of plant biology should have a good understanding of secondary growth.