Dr. T logo BIO 410/510 Plant Anatomy
Dermal tissue: Epidermis

The epidermis is the surface tissue covering all organs of the plant during primary growth

•  Root

Ranunculus root, x.s.
Cross section of Ranunculus root
Micrograph by Biodisc

•  Stem

Helianthus stem, x.s.
Cross section of Helianthus (sunflower) stem with major tissues labeled
Micrograph by John Tiftickjian

•  Leaf

Ligustrum leaf, x.s.
Cross section of a typical dicot leaf. Note upper and lower epidermis, palisade and spongy mesophyll, veins, stomata.
Micrograph by John Tiftickjian

•  Epidermis in surface view

Epidermis surface view
Epidermal peel of Lily epidermis


•  Protection from desiccation

•  Protection from disease organisms

•  Protection from insect damage

•  Gas exchange

•  Secretion


•  Epidermis differentiates from the protoderm

•  Usually one cell thick unless there are periclinal division of protoderm cells. Then you have multiple epidermis.

Ficus leaf, x.s. showing lithocyst. Note how the crystal (the cystolith) hangs from a peg attached to the top of the lithocyst.
Micrograph by John Tiftickjian

Cuticle and waxes

•  In shoots, the outer epidermal cells are covered with the cuticle.

Phormium leaf, x.s.
Cross section of Phormium leaf. Note large areas of supporting fibers and thin-walled parenchyma cells that function in water storage.
Micrograph by John Tiftickjian

•  The cuticle contains the lipid cutin, which is largely impermeable to water (and gases).

•  The development of the cuticle is regarded as one of the important evolutionary steps in the origin of the land plants.

•  Some plants have additional wax layers

•  Cuticle thickness and presence of wax layers is partly a function of habitat.

•  Arid climate species tend to have thicker cuticles

•  Mesic and aquatic plants have thinner cuticles

Cell types

•  ordinary epidermal cells

•  guard cells (in pairs) form stomata

•  trichomes


•  Stucture of guard cells

Stoma seen in face view
Stoma seen in epidermal peel (DIC)
Micrograph by John Tiftickjian

•  Mechanism of opening and closing

•  Radial micellation

Radial micellation
Drawing showing radial micellation and its effect on changing shape of guard cells.
Introduction to Plant Physiology, Copyright John Wiley and Sons

•  Stomata open when guard cells take up water and expand

Stoma mechanism
Illustration of how a stoma opens as guard cells take up water.
Brooker Biology textbook, Copyright McGraw-Hill companies

•  The stomatal complex

•  The pair of guard cells is often surrounded by special cells that differ in shape from the ordinary epidermal cells

•  These surrounding cells are termed subsidiary cells

•  The shape and placement of subsidiary cells result from the pattern division of protoderm cells leading up to the formation of the guard cells.

•  Stomatal complex type has taxonomic value. Many taxa (genus, family) are characterized by a particular type.

•  Common stomatal complex types

Stomatal complexes
Stomatal complex types. Types are defined by the presence and placement of subsidiary cells.

•  Anomocytic. No subsidiary cells. Cells surrounding guard cells are not different that other epidermal cells.

•  Anisocytic. Guard cells surrounded by three subsidiary cells of unequal size.

•  Paracytic. One subsidiary cell on each side of the guard cells oriented parallel to the stoma.

•  Diacytic. One subsidiary cell on each side of the guard cells oriented perpendicular to the stoma.

•  Actinocytic. Several subsidiary cells that radiate from the center of the stoma forming a ring.


•  Trichomes are appendages of the epidermis.

•  Most are hair-like are are commonly called plant hairs.

•  There is a large diversity of forms - examples:

Epidermal trichomes
Types of epidermal trichomes.

•  Can be unicellular or multicellular

•  Can be simple or branched

•  May have secretory function (glandular hairs)

•  Epidermal "peel" with trichomes

Pelargonium leaf epidermis
Pelargonium (geranium) leaf epidermis, w.m. showing stomata and two kinds of trichomes.
Micrograph by John Tiftickjian

•  Complex trichomes are sometimes called scales

•  Peltate scales on leaves of Elaeagnus (whole mount)

Elaeagnus leaf scales
Elaeagnus leaf scales, w.m.
Micrograph by John Tiftickjian

•  Cross section of Elaeagnus leaf showing scale

Elaeagnus leaf scales
Elaeagnus leaf, x.s., showing scales
Micrograph by John Tiftickjian

•  Root hairs

Root hairs
Root hairs on a radish seedling
Photo by John Tiftickjian

•  Root hairs are simple, usually unicellular trichomes found in large numbers near the tips of growing roots.

•  They greatly increase the surface area of the epidermis that is in contact with the soil solution.

•  They increase the efficiency with which the root can absorb water and mineral nutrients.

•  Trichomes are valuable taxonomically and can aid in plant identification.

•  Trichomes have even been used in forensic science.

•  For example, marijuana (Cannabis sativa) has distinctive glandular and nonglandular hairs that are diagnostic. This has provided evidence in drug-related court cases.


•  In plants having secondary growth, the epidermis is temporary. It is replace by the periderm, the secondary dermal tissue.

•  We will cover the periderm later in connection with secondary growth

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