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Leaves (Morphology & anatomy of other leaf types (Succulent leaves…
Leaves
Morphology & anatomy of other leaf types
Spines
Axillary buds on Cacti
No blade and needle shaped
No mesophyll parenchyma
Mesophyll consists of packed fibers
Mature fibers deposit lignin
Makes them hard and resistant to decay
Tendrils
Grow indefinitely
Capable of sensing contact w/ objects
Will coil around the object
Bud scales
Tight layer around stem tip
Primarily for protection
Tougher and waxier than most
Produce thin layer of corky bark
Petiole is short or absent
Leaves of conifers
Leaves are sclerophylls
Contain unpalatable chemicals
Always simple leaves
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Mostly perennial
Produce new phloem, but not xylem
3 are annuals (deciduous)
Larches
Larix
Bald cypress
Taxodium
Dawn redwood
Metasequoia
Leaves with Kranz anatomy
Lack palisade parenchyma & spongy mesophyll
Adapts C4 plants to arid environments
Sclerophyllous foliage leaves
On perennial plants (2 or more years)
Evolved for protection
Plants=sclerophyllous & leaves=sclerophylls
Have thicker cuticle & more waxes
Sclerenchyma is located just below epidermis
Insect traps
Trap and digest insects
Adapted from habitats poor in nitrates and ammonia
Active traps (can move) & passive (incapable of movement)
Succulent leaves
Adaptation to survive in desert habitats
Thick and fleshy leaves
Shape reduces surface-to-volume ratio
Some can be spherical or cylindrical
Favors water conservation
Photosynthesis occurs more deeply than foliage leaves
Internal structure of foliage leaves
Mesophyll
Ground tissue interior to epidermis
Two types
Palisade mesophyll
Contains parenchyma cells
Main photosynthetic tissue of plants
Usually one layer thick
Regions with intense light=3-4 layers thick
Upper portion of the leaf
Spongy mesophyll
Contains aerenchyma cells
Permit CO2 to diffuse rapidly
Prevents CO2 from escaping out stomatal pore
Lower portion of the leaf
Vascular tissues
Between palisade & spongy mesophyll
One large midrib (midvein)
Lateral veins emerge
Branch into narrow minor veins
Releases water from xylem
Loads sugar into phloem
Involved in conduction
Always contain xylem (upper) & phloem (lower)
Conducts and supports leaf blades
Fibers arranged as a sheath=bundle sheath
Bundle sheath extension
Gives rigidity to the blade
Mass of fibers above, below, or both
Epidermis
Water loss=transpiration
Most leaves stomata is in lower epidermis
Trichomes are abundant here
Mostly the epidermis that lines crypts
Provide shade
Deflect sunlight
Catches dew and fog
Prevents blockage of stomatal pores
Contains cutin and wax
Prevents spore from sticking
Petiole
Transition between stem and lamina
Collenchyma is present
Vascular tissue are most variable
1,3, or more vascular bundles=leaf traces
Bears two small flaps in many species
This tissue located at the base=stipules
Protect shoot apical meristem
Contribute to photosynthesis
When leaf is mature, they die early
External structure of foliage leaves
Leaf blade aka lamina
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Light-harvesting portion
Lower side=dorsal surface
Adaxial side, rather smooth
Upper side=ventral surface
Abaxial side, larger viens
May be simple or compound
Simple leaf
Blade of just one part
Compound leaf
Blade divided into several parts
Many small blades=leafets
Attached by a petiolule to the rachis
Petiole (stalk)
Holds blade into the light
Prevents shading of leaf blades
If leafs are small
There may not be a petiole
Leaf is then called sessile leaf
Not called petiolate
Monocots usually lack a petiole
Instead leaf base wraps around stem
This forms a sheathing leaf base
Within a leaf are veins
Bundles of vascular tissue
Eudicots
Usually in a netted pattern=reticulate venation
Monocots
Run side by side=parallel venation
Leaf base
Abscission zone
Perpendicular to the petiole
Release enzymes in autumn
This weakens their cell walls
Adjacent cells swell
Forms protective scar tissue=leaf scar
Usually not formed in monocots
Initiation & development of leaves
Basal angiosperms & eudicots
Leaves produced only through shoot apical meristem
Cells interior to the protoderm
Grow outward, forming protrusion=leaf primordium
Consists of leaf protoderm
Dense cytoplasm and small vacuoles
Consists of leaf ground meristem
Increases in thickness, bulks at the midrib
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Consists of midrib & 2 small wings
Meristematic
Division enlarges the lamina
Lamina expansion
3 more items...
Monocots
Initiated by expansion of shoot apical meristem
Cells adjacent to primordium grow upward with it
Becomes part of primordium
Give the hood-like shape
More cells get involved
Until primordium is a cylinder
This portion grows up=sheathing leaf base
Forms leaf primordium
Gives rise to lamina
Inner=adaxial surface
Outer=abaxial surface
Remain active mitotically
Produces new cells that extend the leaf
Protoxylem & protophloem are constantly stretched
Bulky during this stage
Formed from primordium
Type of leaves
