From Seed to Seed:
Plant Science for K-8 Educators

Tannins and Essential Oils.
Tannins. These water-soluble, bitter, dark-colored substances are found in a variety of barks, woods, leaves, roots, and fruits. Their role in the cell is uncertain. They may serve as a deterrent to herbivores, and may have antiseptic properties useful to the plant.

Tannins are used in the leather industry to cure hides. They bind with the proteins in animal skins, making the proteins unavailable to decay organisms. Tanning a hide creates a stable leather that is resistant to bacterial decay.

Essential oils. These fragrant substances probably play a role in luring pollinators and repelling herbivores. Some essential oils also have antiseptic properties. They are usually fragrant because they evaporate on contact with air. In the plant, essential oils are usually contained in special oil glands or in the region between the cell wall and cuticle of epidermal hairs. Students may notice that simply touching the fuzzy leaves of a mint plant brings out their fragrance. Touching breaks the epidermal hairs and exposes the oils.

Essential oils are used in perfumes and flavorings. Examples include peppermint, spearmint, citrus, eucalyptus, rose, juniper, lavender, and rosemary oils. Many fragrant spices owe their smell to the essential oils they contain, including cinnamon, clove, nutmeg, vanilla, pepper, and ginger.