Anatomy of Monocot Root - Maize

A maize root - the monocot comparison - repeats the bean root's basic outside-in plan (piliferous layer, parenchymatous cortex, casparian-strip endodermis with passage cells opposite the protoxylem, single-layered pericycle) but diverges from it at almost every point of detail once you reach the stele. Where the bean root is tetrarch, the maize root is polyarch - many, rather than four, protoxylem groups arranged around the radial vascular system, still in the same exarch condition (protoxylem toward the periphery). Where the bean root's conjunctive tissue (between the xylem and phloem patches) is parenchymatous and destined to become vascular cambium, the maize root's conjunctive tissue is mostly sclerenchymatous and is never converted into cambium at all - which is exactly why maize, and monocot roots generally, cannot undergo secondary growth or thickening the way a dicot root can. And where the bean root's centre is filled with vascular tissue, the maize root reserves its very centre for a large pith of thin-walled, starch-filled parenchyma with intercellular spaces - a feature the dicot root typically lacks. The pericycle also behaves differently: in the dicot root …