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Chapter 6 (External Structure of Foliage Leaves (Leaf Blade: (dorsal…
Chapter 6
External Structure of Foliage Leaves
Leaf Blade:
flat, light-harvesting portion of leaf
dorsal surface
: lower side of leaf blade
aka abaxial epidermis
ventral surface
: upper side of leaf blade
aka adaxial epidermis
#inner/outer rather than upper/lower
Petiole:
holds blade into light
Simple Leaf
: blade of just one type
Compound Leaf
: blade divided into several individual parts
has many small blades (
leaflets
)
attached by petiolule to the
rachis
palmately compound
: all leaflets attached at same point
pinnately compound
: leaflets attached individually along rachis
Veins: bundles of vascular tissue
reticulate venation
: veins occur in netted pattern (in angiosperms & eudicots)
parallel venation
: larger veins run side by side with few obvious interconnections
Abscision Zone:
usually found in petiole, cells cut off leaf when useful life is over
leaf scar
: cells surrounding petiole base swell/become corky to protect wound
Internal Structure of Foliage Leaves
Epidermis
single layer of cells that covers leaves (upper & lower)
transpiration
: water loss through the epidermis
Mesophyll
ground tissues interior to leaf epidermis
palisade parenchyma
: upper layer of cells, main photosynthetic tissue
separated slightly to increase surface area for CO2 dissolution
spongy mesophyll
: in lower portion of leaf, loosely arranged cells in leave
Vascular Tissues
found between palisade parenchyma & spongy mesophyll
mid-rib
: aka midvein, eudicot usually has one, usually involved in conduction
lateral veins
: usually involved in conduction, emerge from midvein
minor veins
: branch from lateral veins, important for releasing water & loading sugar
contain primary xylem on upper side & primary phloem on bottom
contain primary xylem on upper side & primary phloem on bottom
bundle sheath
: fibers arranged around vasc. tissue, usually midvein & lateral veins
Petiole
stalk that joins leaf to stem
usually contains large amounts of collenchyma
leaf traces
: one/three/five or more vasc. bundles
Morphology/Anatomy of Leaf Types
Succulent Leaves
thick/fleshy leaves that reduces surface-to-volume ratio
inside, mesophyll contains few air pockets, reducing internal evaporative surface area
mesophyll is more transparent, thus light can penetrate further into leaf
good for water retention, but reduced capacity for CO2 uptake
Sclerophyllous Foliage Leaves
leaves are harder than normal with sclerenchyma often present just below epidermis
cuticle usually very thick
leaves known as
sclerophylls
Conifer Leaves:
leaves are sclerophylls; thick cuticle, epidermis & hypoepidermis have thick cell walls
mostly perennial
most contain bitter chemicals to discourage predation
Bud Scales
small, form a tight layer around stem tip
protects dormant shoot apical meristem from low temps & drying wind
often forms corky layer for better protection
Initiation/Development of Leaves
Basal Angiosperms & Eudicots
leaf primordium
: cells interior to protoderm grow outward, forms protrusion
extends upward as narrow cone, grows rapidly
cells in center differentiate into provascular tissue, then primary xylem/phloem
leaf primordium grows & increases in thickness, establishing most of midrib
cells continue to divide & expand, enlarging lamina rapidly
stomata, trichomes, & vascular bundles differentiate
petiole becomes distinct from midrib
consists of leaf protoderm & leaf ground meristem
Monocots
leaf primordium
: cells interior to protoderm grow outward, forms protrusion
apical meristem cells adjacent to primordium grow upward, giving hood-like shape
more cells become involved until primordium is a cylinder that completely/almost encircles shoot apical meristem
shoot apex enlarges, forms new stem tissue, initiates
next leaf primordium
protoxylem & protophloem constantly stretched & disturbed in basal meristem
will develop as tube inside previous leaf’s sheathing base
outer surface: abaxial epidermis
inner surface: adaxial epidermis
