Anatomical Differences Between Root and Stem

Beyond the dicot-versus-monocot contrast examined organ by organ above, root and stem also differ systematically from each other, regardless of which group they belong to, in five recurring ways that Table 9.5 summarises. A root's epidermis has no cuticle and no epidermal pores, and its hairs are always unicellular, since its epidermis is built purely for absorption; a stem's epidermis, built instead to limit water loss while still allowing gas exchange, has both a cuticle and epidermal pores, and its trichomes can be unicellular or multicellular. A root's outer cortical cells never develop chlorenchyma (there is no light underground to make photosynthesis worthwhile), while a stem's outer cortex commonly does. A root's endodermis is characteristically well-defined, with true casparian strips, while a stem's is often ill-defined or effectively absent (the starch-sheath layer, where it exists, is a much weaker analogue). A root's vascular bundles sit in a radial arrangement (xylem and phloem on alternating radii), while a stem's are conjoint (xylem and phloem together on the same radius). And a root's xylem matures exarch (protoxylem toward the periphery), while …