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Summary BOT 2601 LEARNING UNIT 8
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- University Of South Africa (Unisa)
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BOT 2601 LEARNING UNIT 8HERBS, SPICES AND DRUGS
Textbook reference: chapter 11 pg. 383-398
Herbs are derived from leaves and flowers of herbaceous plants and are mild in taste
Spices are derived from stems, seeds and fruit of woody plants and are strong tasting
Drugs are chemicals that possess medicinal value, are psychoactive, or poisonous
Discipline that deals with biological, biochemical and economic aspects of naturally occurring drugs is
pharmacognosy. Involves collection, selection, identification, evaluation, preservation and commerce of drugs
External secretory structures:
Trichomes are outgrowths from the epidermis. They vary in size and may be glandular or stinging types
Glandular trichomes (or glands) have a unicellular or multicellular head composed of secretory cells, usually
borne on a stalk of non-glandular cells. They are found on rose petals, saffron stigmas and styles, hops female
inflorescence bracts, marijuana leaves and flowers, mint and oregano leaves and vanilla fruits
Insectivorous plants that trap insects on the viscid leaf surface have glandular trichomes that secrete nectar,
mucilages or digestive juices
Collectors: a collector is a multicellular appendage or trichome that produces a sticky secretion. They are found
on buds and leaves of woody species
Nectaries: multicellular glandular structures that secrete a liquid containing organic substances including sugar.
They occur in flowers (floral nectaries) and vegetative plant parts (extrafloral nectaries)
Hydathodes: structural modifications of vascular and ground tissues, usually in a leaf, that permit the release of
water through a pore in the epidermis. They have a secretory function
Stigmas: a region of a carpel, at the apex of the style, that is a surface upon which the pollen germinates
Internal secretory structures:
Secretory cavities: glands lined by specialised glandular cells and containing a large secretion-filled space. They
occur in allspice fruits, citrus fruit peels and clove flower buds
Secretory ducts (canals): include resin ducts and gum ducts. Elongated ducts containing a secretion derived
from epithelial cells lining the duct. These are found in chamomile flowers, myrrh stems, tarragon leaves,
parsley leaves and fennel fruits
Laticifers: cells containing latex. Found in opium fruit
ANATOMY OF SECRETORY STRUCTURES:
o The production of oils and resins in plants is associated with glandular trichomes or internal ducts
o Glandular trichomes vary and can be stalked or stalkless
o Stalked glands possess basal cell/s, unicellular/multicellular stalk. unicellular/multicellular round secretory head
o Sessile glands have only a unicellular or multicellular head that accumulates the secretory products
o 3 types of glandular hairs are found on cannabis: bulbous, capitate sessile and capitate stalked
o Capitate sessile forms are attached directly to the organ surface
o Bulbous glands and capitate stalked types have short or tall stalks
o Oil/resin producing glandular trichomes begin with enlargement and division of single protodermal or epidermal
initial. Later divisions form stalk cells in the epidermis. Divisions of stalk cells divide to form additional stalk and
secretory cells. At maturity the head contains enlarged subcuticular space that becomes filled with secretions.
SECRETORY CELLS AND CAVITIES:
o Secretory cells- internal secretory structures associated with wood rays/parenchyma or isolated in fibrous tissue
o Secretory cells are larger than surrounding elements
o Secretory cells include oil cells. Oil cells vary and are visible as transparent dots in the leaf
o Oil cells are spherical and intergrade with mucilage cells
o Mucilage cells can contain bundles of needle-like crystals known as raphides. Painful and prolonged paralysis of
the mouth occurs if the plant parts are chewed. This reaction is caused by the combined action of chemicals with
the ejection of crystal raphides that become embedded in tissues of the mouth and throat
o Internal secretory spaces containing oils or resins are cavities or canals. They arise from groups of cells
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