Anatomy of Dicot Root - Bean

A bean root - the textbook's chosen dicot example - reads, from its outer surface inward, as a clean, orderly sequence. The outermost piliferous layer (epiblema) is a single compact layer of parenchyma with no intercellular spaces, no cuticle and no pores, since its whole purpose is absorption: it bears single-celled root hairs that draw in water and minerals from the soil, alongside a general protective role. Beneath it the cortex is entirely parenchymatous, loosely packed with intercellular spaces that ease gaseous exchange, its oval-to-polygonal (sometimes mutually-flattened polygonal) cells storing starch in leucoplasts even though they carry no chloroplasts of their own. The cortex's innermost layer is the endodermis - barrel-shaped cells bearing casparian strips on their radial and inner tangential walls, except at the passage cells directly opposite the protoxylem, which stay thin-walled to let water and salts cross radially into the stele. Everything inside the endodermis is the stele: a single-layered parenchymatous pericycle (from which lateral roots will later arise, endogenously), and at the centre a radial vascular system with xylem and phloem alternating on separate radii, the xylem exarch (protoxylem outward) and typically tetrarch (four p …