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Leaves (Morphology and Anatomy of Other Leaf Types (Leaves of Conifers #…
Leaves
Morphology and Anatomy of Other Leaf Types
Succulent Leaves
Thick and fleshy
A shape that reduces the surface-to-volume ratio
Favors water conservation
Sclerophyllous Foliage Leaves
Must produce more sugar
Or the plant would loose energy producing leaves
Leaves of Conifers
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Leaves are sclerophylls
Have a thick cuticle
Epidermis and hypodermis cells have thick walls
Contain unpalatable chemicals
Always simple, never compound
Have very few forms
Bud scales
Perennial plants
Dormant shoot apical meristems
Protected from low temperatures
Drying action from wind during winter
Small, rarely compound
Produce a thin layer of corky bark
Spines
Cacti
Green cactus body
Microscopic green leaves
Clusters of spines are their auxiliary buds
Spines are modified leaves of auxiliary buds
Tendrils
Another form of modified leaf
Grow indefinitely
Contain cells that are capable of sensing contact
Grows around object it contacts
Leaves with Kranz Anatomy
C4 photosynthesis
Leaves lack palisade parenchyma
Lack spongy mesophyll
Have permanent bundle sheaths
Composed of large chlorophyllous cells
Insect traps
Plants obtain nitrogen
Needed for their amino acids and nucleotides
Internal Structure of Foliage Leaves
Epidermis
Water loss through the epidermis
Transpiration
Must be reasonable waterproof
Simultaneously translucent
Must allow entry of carbon dioxide
Leaf and stem epidermises are basically similar
Large percent of flat, tabular, ordinary epidermal cells
Guard cells and trichomes may be abundant
Mesophyll
Ground tissues interior to the leaf epidermis
Along the upper surface of most leaves
Layer of cells called the palisade parenchyma
Main photosynthetic tissue of most plants
Layers vary in intensity
Lower portion of the leaf
Spongy mesophyll
Open, loose aerenchyma
Permits carbon dioxide to diffuse away from stoma
Vascular tissues
Between the palisade parenchyma and spongy mesoshyll
Eudicot leaf
One large midrib
Lateral veins
Minor veins
Bundle sheath
Many fibers arranged as a sheath
Veins
Mass of fibers, above, below or both
Bundle of sheath extensions
Help give rigidity to the blade
Petiole
May be tiny but are massive in:
Palms
Rhubarb
Celery
Water lilies
Part of the leaf
Transition between the stem and lamina
One, three or five vascular tissues
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Leaf traces
Branch from stem vascular bundles
Diverge toward the petiole
Bears two small flaps of tissue at its base
Stipules
Protect shoot apical meristem while leaf is young
Contribute to photosynthesis
Usually small and die early
External Structures of Foliage Leaves
Photosynthesis
Leaves absorb carbon dioxide
Convert CO2 to carbohydrates
Must not lose excess amount of water
Must not allow entry of:
Fungi
Bacteria
Epifoliar algae
Cannot be so nutritious to animals it causes liability
Have to be strong enough to survive
Blades
Flat, light-harvesting portion
Leaf blade (lamina)
Blade's lower side
Dorsal surface (abaxial side)
Larger veins protrude like backbones
Upper side
Ventral surface (adaxial)
Rather smooth
Petiole (stalk)
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Holds the blade out into the light
Prevents shading from leaves above them
Allows blade to flutter in the wind
Cooling the leaf
Brings fresh air to the surface
Makes it difficult for insects to land on
Abscission zone
At the leaf base
Oriented perpendicular to the petiole
Involved in cutting off the leaf when useful life is over
Leaf scar
Protective corky layer protects living stem tissues
Sessile leaf
Small or very long and narrow leaves
Sheathing leaf base
Leaf base wraps around the stem
Simple leaf
A blade of just one part
Compound leaf
A blade divided into several individual parts
Has many small blades
Leaflets
Each attached by a petiolule
Extension of the petiole
Rachis
Initiation and Development of Leaves
Basal Angiosperms and Eudicots
Leaf primordium
Extends upward as a narrow cone
As it grows upward it increases in thickness
Monocots
Initiated by the expansion of shoot apical meristem cells
