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Dermal Tissues
Dermal Tissues
Plants have two different types of dermal tissues, depending on the age and form of the plant
Young plants and herbaceous plants only exhibit epidermis
Woody plants will display bark or periderm in older parts
Epidermis
Epidermis
The epidermis of herbaceous tissues will usually exhibit the following structures
Stomata
Stomata
Regulated pores in the epidermis to allow for gas exchange and the release of water vapor through a process called evapotranspiration
Guard cells open and close to regulate gas and water exchange for the plant
Active stomata are regulated by multiple factors including light, atmospheric CO2, and abscisic acid levels (Araujo et al. 2011)
Some ancient plants, like mosses, have stomata that are passively controlled, and other plants like liverworts, only exhibit pores and do not have guard cells
Stomata appear to have evolved once, with novel genes in the first land plants; the active stomatal closure of seed plants resulted from later genes (Bowles et al. 2022)
Cuticle
Cuticle
The cuticle is a protective layer for plants
It has a chemical, called cutin, which provides a layer to prevent desiccation and protect against UV radiation
Hairs
Hairs
Hairs, which are outgrowths of the epidermis, can serve several functions
Some are used to protect from insect herbivory
In arid environments, hairs can be used to retain moisture
Other hairs are hollow, with liquid toxins that are released if the epidermis is disrupted
Prickles are hairs that are sharp and hardened, modified for protection (e.g. rose)
Above: red guard cells of a plant stomata
Below: Scanning electron micrograph of leaf epidermis, with stomata
Above: Stinging hairs of stinging nettle (Urtica dioica)
Above: Sticky hairs of the sundew (Drosera sp.)
Bark
Bark
The outermost layer of woody plant organs (i.e. everything outside of the vascular cambium)
Bark" usually refers to the cork cambium, the products produced by the cork cambium (i.e. phellem & phelloderm), as well as the secondary phloem
The term "periderm" refers to just the cork cambium, phellem, and phelloderm
Therefore "bark" is a combination of the "outer bark" known as the periderm, and the "inner bark" which is the secondary phloem
Phellem cells are usually impregnated with suberin, to act as waterproofing for the trunk
Lenticels, which are parenchyma cells in the bark, serve to allow gas exchange between the atmosphere and stem
Some lenticels are conspicuous, like those found in the bark of birches (Betula) and cherries (Prunus)
Other trees have lenticels, but they are not conspicuous.
Above: prominent lenticels in a paper birch (Betula papyrifera)
Additional Resources
Additional Resources
Piñon pine and juniper react differently to drought than expected (Phys.org 5Aug2025)
└Kraklow et al. (2025) Increased water availability at various timescales has different effects on stomatal closure point in isohydric piñon pine and anisohydric juniper
How plants survive drought: The unsuspected role of myosin XI in guard cells (Phys.org 14Jul2025)
└Liu et al. (2025) Myosin XI coordinates ABA-induced stomatal closure via microtubule stability and ROS synthesis in drought-stressed Arabidopsis
Plant biologists discover an ancient gene family is responsible for plant prickles across species (Phys.org 1Aug2024)
└Satterlee et al. (2024) Convergent evolution of plant prickles by repeated gene co-option over deep time
Microbes living in bark remove methane from the atmosphere (Phys.org 24July2024)
└Gauci et al. (2024) Global atmospheric methane uptake by upland tree woody surfaces
Plants Have Been Keeping a Secret From Us About How Thirsty They Actually Are (13Aug2022ScienceAlert)
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