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Leaves (External Structure of Foliage Leaves (petiole (long, thin= flutter…
Leaves
External Structure of Foliage Leaves
leaf blade
flat, light-harvesting
aka lamina
dorsal surface
blades lower side
contains large veins like backbones
aka abaxial side
ventral surface
upper side
aka adaxial
usually smooth
petiole
stalk
holds blade out into the light
prevents shading of leaf blades by others
long, thin= flutter in the wind to cool leaf
brings fresh air to surface
makes it difficult for bugs to land
sessile leaf
leaf w/o petiole
small or very long & narrow
Aeonium
simple leaf
blade of just one part
bugs or fungus can spread rather easily
compound leaf
blade divided into several individual parts
leafflets
many small blades
attached by a petiolule
then to an extension of the petiole, the rachis
veins
bundles of vascular tissues
distribute water from the stem into the leaf
collect sugars & carry them to the stem
in basal angiosperms & eudictos,
occur in a netted pattern called reticulate ventation
abscission zone
cells involved in cutting off the leaf when its life is over
Morphology and Anatomy of Other Leaf Types
Succulent Leaves
survive in desert habitats
contains families such as:
Crassulacae
Portulacaceae
Aizoaceae
thick and fleshy
shape that reduces the surface-to-volume ratio
consequence of reducing the capacity for CO2 uptake
favors water conservation
mesophyll contains very few air spaces
photosynthesis occurs more deeply
Sclerophyllous Foliage Leaves
must produce more sugars by photosynthesis
limited amount of sclerenchyma
most leaves tend to be soft, flexible, and edible
extended lifetime and prolonged productivity
more resistant to animals, fungi, freezing temps, and UV light
Leaves of Conifers
leaves are sclerophylls
thick cuticle
epidermis and hypodermis have thick walls
contain unpalatable chemicals
always simple, never compound
only few forms
needles occur in all pines, firs, and spruces
mostly perennial
remaining on the stem for many years
plants are evergreens
Bud Scales
one of the most common modifications of leave converson
role is primarily protection
structure differs from foliage leaves
small, rarely compound
petiole is either short or absent
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tougher and waxier than most regular leaves
produce a thin layer of corky bark
Spines
cacti
spines are their axillary buds
the spines are modified leaves of axillary buds
distinct structure
have no blade and are needle shaped
no mesophyll parenchyma or vascular tissue
Tendrils
peas, cucumbers, squash
another form of modified leaf
contain cells that are capable of sensing contact
when it touches something, the side facing the object stops growing
Insect Traps
ability to trap and digest insects
obtains the nitrogen they need for their amino acids and nucleotides
numerous stomata and vascular bundles
mesophyll containing aerenchyma and chlorenchyma
lamina is tubular rather than flat
secrets a watery digestive fluid
after digestion and absorbtion
the midrib motor cells fill with water, swell, and force trap open
Internal Structure of Foliage Leaves
Mesophyll
ground tissues interior to the leaf epidermis
palisade parenchyma
layer of cells along upper surface
main photosynthetic tissue of most plants
large surface area
allows for max dissolution
usually one layer thick
regions w intense sun, it can be 3 to 4 layers
spongy mesophyll
lower portion of leaf
open, loose
permits CO2 to diffuse rapidly
Vascular Tissue
between the palisade parenchyma & spongy mesophyll
midrib
aka midvein
lateral veins emerge this branch into narrow minor veins
minor veins release water from xylem
also load sugar into phloem
mostly involved in conduction
support the leaf blade
bundle sheath
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many fibers arranged as a sheath
makes it difficult for insects to chew into vascular tissue
bundle sheath extensions
mass of fibers above or below large veins, or both
Epidermis
transpiration
water loss through the epidermis
cutin
wax on the outer wall
Petiole
tiny
massive in plants such as:
palms
celery
rhubarb
water lilies
transition between the stem and the lamina
the epidermis contains fewer stomata and trichomes
the mesophyll is like a cortex
vascular tissue is the most variable
1, 3, 5, or more vascular bundles= leaf traces
they branch from stem vascular bundles
then diverge toward the petiole
stipules
2 small flaps of tissue at the base
serve various functions
Initiation and Development of Leaves
Basal Angiosperm and Eudicots
apical meristem
leaf primordium
cells just interior to the protoderm that grow outward
monocots
leaves are initiated by the expansion of some shoot apical meristem cells