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Leaves (External Structure of Foliage Leaves (Petiole (prevents shading of…
Leaves
External Structure of Foliage Leaves
Leaf Blade
also called the lamina
flat
light-harvesting
Dorsal Surface
blades lower side
synonym; abaxial side
Ventral Surface
the upper side
usually smooth
synonym; adaxial side
Petiole
most leaves contain one
stalk
holds blade out into sunlight
prevents shading of other leaves
by those above them
Sessile Leaf
small
long-narrow
self-shading is not a problem
no petiole
Sheathing Leaf Base
typically lack petiole
wraps around the stem
forming a base
Simple Leaf
blade consists of one part
Compound Leaf
blade divided in different parts
leaflets
thread-like
blades attached to compound leaf
each attached to a petiole
extension of petiole
rachis
smaller blades
Veins
within a leaf
bundles of vascular tissue
distribute water from stem
simultaneously collect sugars
carry them for storage
for use
produced by photosynthesis
Reticulate Venation
occurs in a netted pattern
Parallel Venation
larger veins
run side by side
few obvious interconnections
Abscission Zone
located at leaf base
usually in the petiole
#
cells cut off leaf
when useful life is over
releases enzymes
weakens cell walls
Leaf Scar
protective scar tissue
around the wound
undamaged cells
swell
become corky
Morphology and Anatomy of Other Leaves
Succulent Leaves
survives in desert habitats
most common production
thick
fleshy
reduces surface-to-volume ratio
favors water conservation
inside leaf
mesophyll contains few air spaces
more transparent
photosynthesis occurs more deeply
Sclerophyllus Foliage Leaves
must produce more sugar
tend to be soft
flexible
edible
extended lifetime and productivity
leaves are feasible
more resistant
sclerenchyma is present
as a layer
cuticle is usually thick
Leaves of Conifers
sclerophyllus
thick epidermal walls
contains unpalatable chemicals
always simple
#
Bud Scales
most common modification of leaves
protect shoot apical meristems
from low temperature
from drying action during winter
form layer around stem tip
primary role is protection
not photosynthesis
small and rarely compound
petiole is short or absent
remain close to the stem
tough and waxy
Spines
does not contain
mesophyll parenchyma
vascular tissue
cells die and dry out
harden even further
fibers deposit lignin
hardens the spine
resistant to decay
Tendrils
peas
cucumbers
squash
grows indefinitely
cells within sense contact
with another object
Leaves with Kranz Anatomy
special metabolism
C4 photosynthesis
lack
palisade parenchyma
spongy mesophyll
contains
prominent bundle sheaths
composed of large chlorophyllus cells
surround sheath
ring of mesophyll cells
radiate from vascular bundles
carbon dioxide transport
adapts C4 plants
to arid environments
Insect Traps
grows in habitats
poor in nitrate
contains ammonia
digests insects
obtain nitrogen they need
production of amino acids
production of nucleotides
similar to foliage leaves
#
unfold after digestion is over
Internal Structure of Foliage Leaves
Epidermis
transpiration
water loss through epidermis
must be reasonably waterproof
also translucent
must allow entry of carbon dioxide
ordinary epidermal cells
trichomes
guard cells
leaf epidermis
remarkably hairy
stem epidermis
cells contain
coating of cutin
wax on their walls
retain water
smooth-slippery surface
Mesophyll
contains
ground tissue
interior to leaf epidermis
#
palisade parenchyma
also called palisade mesophyll
main photosynthetic tissue in plants
often one layer thick
regions penetrated by sunlight
spongy mesophyll
lower portion of leaf
open-loose aerenchyma
permits carbon dioxide to diffuse
away from stomata
Vascular Tissue
occurs between
palisade parenchyma
spongy mesophyll
midrib
also called midvein
lateral veins emerge
narrow minor veins
bundle sheath
many fibers
arranged into a sheath
useful against predators
bundle sheath extension
mass of fibers
below
above
makes blades ridged
helps with water transport
Initiation and Development of Leaves
Basal Angiosperms and Eudicots
leaf primordium contains
leaf protoderm
leaf ground meristem
cells are meristematic
dense cytoplasm
small vacuoles
base of meristems
cells interior to the protoderm
grows outward
forming a protrusion
extends as a narrow cone
growing rapidly
becomes taller than shoot apical meristem
Monocots
leaves initiated by
expansion of apical meristems
grow upward
form a leaf primordium
merging leaf primordium and apical meristem
giving a hood-like shape
lamina becomes broad
constant basal expansion
protoxylem
protophloem
stretched and disrupted
