Chapter 23: Cells and Tissues of the Plant Body

Cells and Tissues of the Plant Body meristematic regions produce three primary meristems—protoderm, procambium, and ground meristem—that differentiate into the three major tissue systems structuring the plant body. Plant development occurs through three interconnected processes: growth as the irreversible increase in size through cell division and enlargement, morphogenesis as the establishment of plant form and structure, and differentiation as the specialization of cells based on their positional cues rather than their developmental lineage. The ground tissue system comprises parenchyma cells, which are living, metabolically active, and capable of diverse functions including photosynthesis, nutrient storage, and wound healing; collenchyma cells, which provide mechanical support to young or growing organs through asymmetrically thickened walls; and sclerenchyma cells, which reinforce mature tissues through heavily lignified secondary walls, existing as either elongated fibers or irregular sclereids. The vascular tissue system includes xylem, which transports water and minerals while providing structural support through tracheary elements such as tracheids and vessel elements, and phloem, which conducts sugars and signals through sieve elements, including sieve-tube elements in angiosperms that function with metabolically dependent companion cells. The dermal tissue system encompasses the epidermis, a protective layer covered by a waxy cuticle that reduces transpiration and includes specialized structures such as guard cells regulating stomatal apertures, trichomes serving protective or absorptive functions, and in woody plants, periderm tissues including cork, cork cambium, and phelloderm that replace the epidermis and provide secondary protection. Together, these tissue systems create an integrated structural framework enabling plants to acquire resources, transport materials, and respond dynamically to their environment throughout their growth.