[Image:Stem-histology-cross-section-tag.svg|thumb|right|Cross-section of a
flax plant stem:
1.
Pith 2.
Protoxylem 3.
Xylem I
4.
Phloem I
5.
Sclerenchyma (
bast fibre)
6. Cortex
7.
Epidermis]] A
cortex is the outermost layer of a stem or root in a plant, or the surface layer or "skin" of the nonfruiting part of the body of some
lichens.