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Ch.6 Leaves (Morphology of Other Leave Types (Insect Traps (trichomes &…
Ch.6 Leaves
Morphology of Other Leave Types
Succulent Leaves
leaves thick and fleshy
reduces surface-to-volume-ratio
favors water conservation
spherical or cylindrical
reduces CO2 uptake
mesophyll has few air spaces
reduces internal evaporation
reduces water loss through stomata
more transparent
light penetrates further into leaf
photosynthesis occurs more deeply
examples
crassulace
portulacacae
arizoaceae
Sclerophyllous Foliage Leaves
must produce more energy then uses
limits sclerenchyma in foliage leaves
leaves soft
flexible
edible
located layer below epidermis, in bundle sheaths
thick cuticle
waxes abundant
perennial
last 2 or more yrs.
sclerenchyma feasible/hardy
more resistant
Conifer Leaves
leaves sclerophylls
thick cuticle
epidermis & hypodermis cells thick walls
contain unpalatable chemicals
always simple
short or long needles
some 40 cm long
most 10 cm long
examples
spruces
pines
firs
small/flat needles
scale like
shield covering stems
12 cm length, 3.5 width
examples
junipers
cypresses
arborviate
Bud scales
small, rarely compound
petiole short or abesent
must remain close to stem & be folded over it
tougher and waxier
thin layer corky bark
protection
common modification of leaves
protect from wind & low temps
Spines
protect moist body
spine has no blade
needle shaped
no mesophyll & vascular tissue
mesophyll consists of closely packed fibers
lignin in walls
makes hard
resistant to decay
Cacti have two types leaves
microscopic
clusters of spines
Tendrils
modified leaf
grow indefinitely
cells capable of sensing contact w/other objects
coils around object touches
no lamina forms
Kranz Anatomy Leaves
C4 photosynthesis
special metabolism
lack parenchyma & spongy mesophyll
prominent bundle sheaths
composed of large chlorophylous cells
surrounds sheaths ring of mesophyll cells
possess mechanism of CO2 transport
Insect Traps
environments w/poor nitrates & ammonia
active traps
upper surface covered w/glandular trichomes
ex:) sundev leaves
passive traps
incapable of movement
ex: pithcer leaves of nepenthes darlingtonia & sarracenia
similar to foliage leaves
lamina tubular
secretes watery digestive fluid
epidermis in digestive region absorptive
trichomes & lamina must sense & respond to insect
carry on secretion & absorption
unfold after digestion
Internal Structure of Foliage Leaves
Epidermis
transpiration
water loss through the epidermis
serious problem in dry soil
epidermis must be reasonably waterproof
simultaneously translucent
must allow CO2 entry
large % flat, tubular, ordinary epidermal cells
guard cells and trichomes ( glandular or nongladular)
more stomata in lower level of leaves
benefit
less water loss
spores land on top, can't penetrate easily
sunken epidermal cavities
region of nonmoving air
hairy
trichomes
protect from insects
harder to walk on
harder to chew
protect from animals
stinging
downside
shade plants upper surface
benefits
rapid air movement
slow water loss
cells
contain waxy coating
retain water
digestion by fungi dificult
smooth slippery prevents spores
Mesophyll
ground tissues interior to leaf epidermis
palisade parenchyma
along the upper surface
main photosynthetic tissue
seperated slightly
extracellular space
often one layer thick
spongy mesophyll
lower potion of leaf
open, loose arenchyma
permits CO2 to diffuse rapidly
sun-over-head
parenchyma near upper surface
vertical leaves
palisade parenchyma equal both sides
Vascular Tissues
between palisade parenchyma parenchyma and spongy mesophyll
midrib (midvein)
conduction
lateral veins emerge
branch into minor veins
release water from xylem
load sugar into phloem
bundle sheath extension
mass of fibers
give rigidity
moves H20 from bundle out to mesophyll
primary xylem upperside
primary phloem lower side
fibers arranged in bundle sheath
around vascular tissue
minor veins
sites of material exchange w/rest of mesophyll
large surface are
contact w/palisade and spongy mesophyll
Petiole
tiny
massive in plants
palms
rhubarb
celery
water lilies
part of leave & transistion between stem and lamina
arrangement diff @ both ends
epidermis fewer stomata & trichomes
petiole mesophyll
like cortex
somewhat compact
not especially arenchymatous
considrable collenchyma present
supports heavy lamina
leaf traces
branch from stem vascular bundle
diverge toward petiole
may be distint
may fuse into single track
vascular bundles fuse w/in petiole or branch further
ring
plate
patterns
External Structure of Foliage Leaves
Function
photosynthesis
to retain water
protection against invaders
be not too nutritious/tasty
cheap enough for plants to make
Parts
leaf blade
dorsal surface
blades lower side
larger veins
ventral surface
blade upper side
rather smooth
flat, light harvesting portion
types
simple
greater % composed of photosynthetic cells
blade of leave one part
compound
pinnately
leaflets attached individually
palmately
leaflets attached @ same point
great deal of nonphotosynthetic
blade divided into many parts
prevents tearing
many leaflets
small blades
attached @ extension of ranchis
petiole (stalk)
prevents shading from leaves above
self shading consequence
holds blade into light
flutter in wind
fresh air
still in wind
Co2 absorbed faster
photosynthesis slower
sheathing leaf base
leaf wraps around the stem.
occurs in most monocots
ex) grasses
ex) irises
ex) agaves
ex) yuccas
sessile leaf
instead of petiolate
ex) aeonium
small, long and narrow
self shading not problem
veins
bundles of vascular tissue
distribute water from stem into leaves
simultaneously collect sugars produced
carry to stem for storage
venation
reticulate
in angiosperms & eudicots
nettled pattern
parallel
in monocots
long, strap shaped leaves
larger veins
run side by side
abscission zone
@ leaf base
perpendicular to petiole
cells cut leaf when not useful
enzymes release that weaken cell wall
leaf twists and breaks off
scar tissue
forms over wound
corky
Initiation and Development
Basal Angiosperms & Eudicots
leaves only produced through apical meristem
@ base of meristem cells grow outward
protrusion called leaf primordium
extends upward as narrow cone
grows rapidly becoming taller
consists of
leaf protoderm
leaf ground meristem
strand cells differentiate
provascular tissue
primary xylem & phloem
forms connection w/young bundles
grows upward
increases thickness
bulk of midrib
row of cell in primordium grows outward
initiates lamina
expansion
differentiates
stoma
trichomes
vascular bundles
petiole
perennial plants
leaves initiated in winter or autumn
reach developmental stage
dormant
bud opens in spring
primordial leaves expand rapidly
little to no mitosis
Monocots
initiated by shoot apical meristem cells
form leaf primordium
apical meristem cells adjacent grow upward
become part of primodium
hood like shae
primordium becomes a cylinder/encircles shoot
tube portion grows upward
shealthing base
original conical leaf primordium gives rise to lamina
outer surface abaxial epidermis
inner surface adaxil epidermis
shoot apex enlarges
forms new stem tissue
first leaf @ full size
continues elongating
emerges through leaf's tubular sheathing base
basal expansion
protoxylem & proyophloem
stretch
distrupt
vessel elements % sieve tube members differentiate
rapid
conduction never interrupted
