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Ch 6: LEAVES (External Structures of the Foilage Leaves (leaves carry…
Ch 6: LEAVES
External Structures of the Foilage Leaves
leaves carry water
externally tough
leaves absorb CO2
thick layer of chlorenchyma
monocots can be self shaded
simple leaf= one part blade
compound leaf=several blades
compound leaf is attached to a petiolule
compounded leaves are better adapted
foilage matters
leaf shape= plant identification
leaf base=petiole=abscission
Internal Structures of the Foilage Leaves
dehydration synthesis in epidermis=transpiration
trichomes can affect amount of sunlight recieved
fog, water droplets condense on trichomes
Mesophyll
upper surface of leaves= palisade parenchyma
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spongy mesophyll=lower portion of leaf
Vascular Tissues
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Minor vein release water from xlyem
vein structure changes with size
many fibers arranged= bundle sheath
Petiole
transition between the stem and lamina
Petiole mesophyll is like cortex
flaps of tissue is stipules
stipules protect apical meristem while young
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Morphology and anatomy of other leaf types
Succulent leaves
survive desert habitats
thick and fleshy
lack of air spaces= mesophyll more transparent
photosynthesis occurs during mild microclimate
sclerophyllous foliage leaves
produce more sugars by photosynthesis
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sclerenchymatous leaves are feasible
plants are sclerophyllous leaves are sclerophylls
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Leaves of Conifers
epidermis and hypodermis cells have thick walls
contain palatable chemicals
always simple
Bud scales
bud scales protect plant from various temperatures
primarily for protection
tougher and waxer than regular leaves
spines
cactus spines are modified leaves
excellent source of water
no mesophyll parenchyma or vascular tissue
mesophyll is packed fibers
tendrils
grow indefinitely
sense contact with an object
lamina= detriminal
C4 photosynthesis lack palisade parenchyma
process a mechanism of CO2
insect traps
trap an digest insects
plants obtain nitrogen
numerous stomata and vascular bundles
example: venus flytraps
midrib helps close and open trap
Initiation and development of leaves
Basal Angiosperms and Eudicots
primordium consists of leaf protoderm
young leaf consist of a midrib and 2 wings
entire pattern is complete when leaf is small
Perennial plants=leaves open in summer
perennial plants= spring the bud opens
initiates leaves before before the seed becomes dormant
monocot
apical meristem initiates to form leaf primordium
outer surface of tube= abaxial epidermis
inner surface tube= adaxial epidermis
remain active producing new cells
protoxylem and protophloem are stretched and disrupted
above basal meristem=tissues mature
differentiation is oriented upside down
broad succulent stems store water
only generate new epidermis at shoot
