cross section: Zea root common name: Corn magnification: 100x

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The epidermis consists of a single layer of barrel shaped cells with no apparent cuticle. Root hairs appear as unicellular extensions of epidermal cells.

The cortex is well-developed and roughly divisible into two zones; a narrow outer layer of smaller closely packed parenchyma cells and a wide inner layer of slightly more open aerenchyma cells. In older roots, the outer cortex appears as an exodermis of sclerenchymized collenchyma cells.

The inmost area of the cortex is bounded by an endodermis of elongated cells whose walls show a narrow band of suberization, marking the Casparian stip.

The outer stele is bound by a pericycle layer of thin walled parenchyma cells. The vascular bundles are radially arranged with short arms of xylem interspaced with patches of phloem and parenchymous conjunctive tissue. The xylem is exarch: meaning the older smaller protoxylem is found towards the periphery and younger larger metaxylem to the center of the stem. Phloem tissues of sieve tubes, companion cells and phloem parenchyma are also exarch. The older protophloem is found towards the periphery and the younger metaphloem towards the center of the stem. Phloem parenchyma may become sclerenchymized in older roots. Vascular cambium is absent, preventing secondary growth of the root.