Cortex, in plants, tissue of unspecialized cells lying between the epidermis (surface cells) and the vascular, or conducting, tissues of stems and roots. Cortical cells may contain stored carbohydrates or other substances such as resins, latex, essential oils, and tannins. In roots and in some herbaceous stems but not usually in woody stems, the innermost layer of cortical cells is differentiated into a cell layer called the endodermis. The cell walls of the endodermis possess a woody and corky band, called the casparian strip, around all the cell walls except those facing toward the axis and the surface of the root or stem. The endodermis with its casparian strips may function in regulating the flow of water between outer tissues and the vascular cylinder at the centre of the root. Within an inch or two of shoot tips, some flowering plants have a starch sheath (a layer of cells with much stored starch) in the same position as an endodermis.
The cortex often develops into a type of tissue called aerenchyma, which contains air spaces produced by separation, tearing, or dissolution of the cortex cell walls. Cortical cells in herbaceous stems, young woody stems, and stems of succulents (cacti and other fleshy plants) contain chloroplasts and can therefore convert carbon dioxide and water to simple carbohydrates (carbon fixation) using photosynthesis. Simple carbohydrates may then be metabolized into complex carbohydrates such as starch, which is stored in the cortex in edible roots, bulbs, and tubers.
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The cortex conducts water and dissolved minerals across the root from the epidermis to the vascular cylinder, whence it is transported to the rest of the plant. The cortex also stores food transported downward from the leaves through the vascular tissues. The innermost layer of the…
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collenchyma
…is found chiefly in the cortex of stems and in leaves and is the primary supporting tissue for many herbaceous plants. In plants with secondary growth, the collenchyma tissue is only temporarily functional and becomes crushed as woody tissue develops. It often constitutes the ridges and angles of stems and…
ADDITIONAL MEDIA
Figure 9: Cross section of a typical root, showing the primary xylem and phloem arranged in a central cylinder.
Figure 8: Tissue organization in a stem tip.
Figure 4: A summary of the primary and secondary growth of a woody dicotyledon.
MORE ABOUT Cortex
5 REFERENCES FOUND IN BRITANNICA ARTICLES
Assorted References
collenchyma
In collenchyma
root anatomy
In root: Morphology and growth
In angiosperm: Roots
stem structure
In plant: Stems
In tree: General features of the tree body
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