cortex (botany)
{{Short description|Outer layer of a stem or root in a vascular plant}}
File:Stem-histology-cross-section-tag.svg plant stem:
1. Pith
2. Protoxylem
3. Xylem I
4. Phloem I
5. Sclerenchyma (bast fibre)
6. Cortex
7. Epidermis]]
In botany, a cortex is an outer layer of a stem or root in a vascular plant, lying below the epidermis but outside of the vascular bundles.{{cite book |last1=Allaby |first1=Michael |editor1-first=Michael |editor1-last=Allaby |title=A Dictionary of Plant Sciences |publisher=Oxford University Press |language=en |doi=10.1093/acref/9780198833338.001.0001 |date=2019|isbn=978-0-19-883333-8 }} The cortex is composed mostly of large thin-walled parenchyma cells of the ground tissue system and shows little to no structural differentiation.{{cite book |last1=Hine |first1=Robert |editor1-first=Robert |editor1-last=Hine |title=A Dictionary of Biology |publisher=Oxford University Press |doi=10.1093/acref/9780198821489.001.0001 |date=18 April 2019|isbn=978-0-19-882148-9 }} The outer cortical cells often acquire irregularly thickened cell walls, and are called collenchyma cells.{{Cite journal |last=Leroux |first=Olivier |date=November 2012 |title=Collenchyma: a versatile mechanical tissue with dynamic cell walls |journal=Annals of Botany |language=en |volume=110 |issue=6 |pages=1083–1098 |doi=10.1093/aob/mcs186 |issn=1095-8290 |pmc=3478049 |pmid=22933416}}
Plants
= Stems and branches =
In the three dimensional structure of herbaceous stems, the epidermis, cortex and vascular cambium form concentric cylinders around the inner cylindrical core of pith. Some of the outer cortical cells may contain chloroplasts, giving them a green color. They can therefore produce simple carbohydrates through photosynthesis.{{Cite book |last=Capon |first=Brian |title=Botany for Gardeners |publisher=Timber Press |year=2010 |isbn=978-1-60469-095-8 |edition=3rd |location=Portland, Oregon |pages=62,77,85}}
In woody plants, the cortex is located between the periderm (bark) and the vascular tissue (phloem, in particular). It is responsible for the transportation of materials into the central cylinder of the root through diffusion and may also be used for storage of food in the form of starch.{{cite book |title= Botany Illustrated: Introduction to Plants, Major Groups, Flowering Plant Families |author=Janice Glimn-Lacy |author2=Peter B. Kaufman |edition= illustrated |publisher= Springer Science & Business Media |year= 2012 |isbn= 978-94-009-5534-9 |page= 13}}
= Roots =
In the roots of vascular plants, the cortex occupies a larger portion of the organ's volume than in herbaceous stems. The loosely packed cells of root cortex allow movement of water and oxygen in the intercellular spaces.
One of the main functions of the root cortex is to serve as a storage area for reserve foods. The innermost layer of the cortex in the roots of vascular plants is the endodermis. The endodermis is responsible for storing starch as well as regulating the transport of water, ions and plant hormones.
Lichen
On a lichen, the cortex is also the surface layer or "skin" of the nonfruiting part of the body of some lichens.[https://www.anbg.gov.au/lichen/what-is-lichen.html What is a lichen?, Australian National Botanical Garden] It is the "skin", or outer layer of {{lichengloss|thallus}} tissue, that covers the undifferentiated cells of the {{lichengloss|medulla}}. Fruticose lichens have one cortex encircling the branches, even flattened, leaf-like forms. Foliose lichens have different upper and lower cortices. Crustose, placodioid, and squamulose lichens have an upper cortex but no lower cortex, and leprose lichens lack any cortex.{{Citation needed|date=August 2023}}