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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, fleshly
Shape favors water conservation
Reduces capacity for CO2 intake
Sclerophyllous Foliage Leaves
Soft, flexible and edible because of limited sclerenchyma
Some exist on a plant for 2 years or more
More feasible and resistant
Leaves of Conifers
Thick cuticle and cell walls
Always simple
The small scale-like leaves form a shield like covering
Leaves remain for many years
Bud Scales
Protect shoot apical meristem
Small and rarely compound
Petiole is short or absent
Tougher and waxier than regular leaves
Spines
Modified leaves of axillary buds
No mesophyll parenchyma, but have closely packed fibers
Deposit lignin, hardening them
Photosynthesis in stem cortex
Tendrils
Grow indefinitely, cells sense contact
The touches side stops growing
The untouched side continues to elongate
Tendrils coil around object
Reorient the lamina for max photosynthesis
Leaves with Kranz Anatomy
Lack palisade parenchyma and spongy mesophyll
Adaptation is mostly due to location and environment (Crosslink)
Have prominent bundle sheath composed of large chlorophyllous cells
Ring of mesophyll cells
Adapts to arid enviroments
Insect Traps
Sundew- glandular trichomes secrete a sticky digestive liquid
Insect is caught, trichomes bend, placing their digestive drops on it
The entire leaf blade curls around insect
Venus flytrap
Bug rubs against trigger hairs
Midrib motor cells lose water quickly
Trap rapidly closes
Glands secrete digestive liquid
After digestion, fills with water, forcing trap to open
Throat contains numerous trichomes pointing toward liquid
External Structure of Foliage Leaves
Leaves are flat for maximum exposure to light
Leaf Blade
Lower Side- Dorsal Surface
Upper Side-Ventral Surface
Shading
Petiolate-Petiole-Leaf stalk
Sessile leaf- no petiole
Sheathing leaf base
Number of leaf blades
Simple- blade has one part
When wind over the leaves , it flows more smoothly over the simple leaf and the compound leave has more turbulence, losing CO2 (crosslink)
Compound- blade is divided
Leaflets
Petiolule- the leaflet is attached
Rachis- the extension of the petiole
Veins- bundles of vascular tissue
Reticulate veins- netted venation
Parallel venation- large veins that run side by side
Dying leaf
Abscission zone
Leaf scar- protective scar tissue for other cells
Internal Structure of Foliage Leaves
Epidermis
Transpiration- water loss through epidermis
Stomata in the upper epidermis-lose water
Most leaves has less stomata on the upper epidermis
Some leaves has no stomata on the upper epidermis
Stomata on the underside of the leaf- reabsorbs its water
Stomata much more numerous on underside
Leaf hairs
Provide some shade
Makes walking or chewing difficult
Some secrete stinging compounds
Underside hair
Prevents rapid air movement
Slows water loss
Mesophyll- ground tissue interior of leaf epidermis
Palisade parenchyma- main photosynthetic tissue
Mostly one cell layer thick
Some leaves palisade parenchyma on both sides
The spongy mesophyll is either in the center or lacking
Some 3 to 4 layers for intense, penetrating sunlight
Spongy mesophyll-lower portion of leaf
Loose aerenchyma that permits diffusion to all parts of leaf
Vascular Tissue
Mid-rib or a midvein
Lateral veins emerge from midrib
Minor veins emerge from lateral veins
Minor veins release water from xylem
Minor veins- site for material exchange
Involved in conduction
Upper side- primar xylem
Bundle sheath- around vascular tissue
Bundle sheath extension
Lower side- primary phloem
Petiole- the transition between stem and lamina
Leaf traces- vascular tissue that is vascular bundles
Some would fuse into a single trace
Some divide into numerous bundles
Fuse with other vascular bundles in the petiole
Or they branch further
Can be arranged in a ring or a plate
Initiation and Development of Leaves
Basal Angiosperms and Eudicots
Leaf primordium- upward narrow cone
Leaf protoderm and leaf ground meristem
Center leaves turn into xylem and phloem
The primordium grows a midrib and wings
Compound leaves
Initiate leaflets
Perennial plants
Before they mature, they become dormant
In the spring primordial leaves expand
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Apical meristem grow giving a hood-like shape
Grows in a cylinder shape that encircles shoot apical meristem
Growing as a sheath leaf base
Outer surface- abaxial epidermis
Inner surface- adaxial epidermis
Shoot apex enlarges, forming new stem tissue
Monocots
Species grow the same at first (crosslink)
