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Chapter 6: Leaves (Morphology and Anatomy of other Leaf Types (Conifer…
Chapter 6: Leaves
External Structure of Foliage Leaves
leaf blade/lamina
structure
dorsal surface
large veins protrude as a backbone
ventral surface
smooth
petiole
allows leaf flutter
holds blade into the light
sessile leaf
leaf without petiole
sheathing leaf base
types
simple
blade with just one part
compound
blade divided into several individual parts
has leaflets
rachis
#
palmately compound
pinnately compound
abscission zone
#
oriented perpendicular to the petiole
adjacent undamaged cells for leaf scar
Internal Structure of Foliage Leaves
mesophyll
upper leaf
palisade parenchyma
good area for dissolution
lower leaf
loose aerenchyma
carbon dioxide diffuses rapidly away from stomata
"spongy mesophyll"
vascular tissue
midrib/midvein
lateral veins emerge from
branch into minor veins
bundle sheath
around vascular tissue
causes difficulty for insects trying to eat
nonconducting cells
mucilage
starch storing cells
vascular bundles
epidermis
water is lost here through transpiration
must be reasonably waterproof and translucent
must allow for the entry of Carbon Dioxide
types
leaf
ordinary epidermal cells
guard cells and trichomes
cutin on cell walls
stem
ordinary epidermal cells
guard cells and trichomes
petiole
tiny
important in many plants
rhubarb
celery
palms
water Lillies
transition between stem and lamina
fewer stomata and trichomes
leaf traces
#
may remain distinct
may fuse in a single trace
stipules
can contribute to photosynthesis
protect the shoot apical meristem
Initiation and Development of Leaves
Basal Angiosperms and Eudicots
leaf primordium
extends upward as a narrow cone
establishes bulk of midrib
becomes taller than shoot apical meristem
all cells in wings are meristematic
lamina expansion
#
stomata, trichomes, and vascular bundles differentiate
initiating perennial plants
in the summer or autumn
before they mature
little mitosis will occur
mainly maturation
Monocots
initiated by expansion of shoot apical meristem cells
apical meristem cells grow along with the primordium
provides hoodlike shape
outer surface of tube
abaxial epidermis
(in some) lamina can become broad
constant basal expansion
interrupts protoxylem and protophloem
broad succulent stem
store water
have accordion-like pleated surface
#
Morphology and Anatomy of other Leaf Types
Conifer Leaves
thick cuticle and walls
never compound
examples
cypresses;
Cupressus
arborvitae;
Thuja
Modified leaves
Spines
have no blade
mesophyll consists of closely packed fibers
Tendrils
grow indefinitely
contain cells that can sense contact with an object
Bud Scales
primary role is protection
small and rarely compound
Sclerophyllous Foliage Leaves
produce more sugars than used
examples
holly
agave
Leaves with Kranz Anatomy
lack palisade parenchyma and spongy mesophyll
ring of mesophyll around sheath
special mechanism to transport Carbon Dioxide
Succulent Leaves
permit plants to survive in deserts
mesophyll contains very few spaces
example
Stone plants;
Lithops
Insect Traps
similar to foliage leaves
examples
Venus flytraps; Dionaea muscipula
leaves of sundew;
Drosera
