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Leaves (Morphology and Anatomy of Other Leaf Types (Succulent Leaves…
Leaves
Morphology and Anatomy of Other Leaf Types
Succulent Leaves
survive in desert
Crassulaeae
Portulaca and Lewisia
Portulacaceae
Kalanchoe and Sedum
Aizoaceae
ice plants
thick and fleshy
shape that reduces the surface-to-volume ratio
some cylindrical, some spherical
advantageous for water retention
favors water conservation
mesophyll contain few air spaces
reduces internal evaporative SA
also water loss through stomta
photosynthesis more deeply
Sclerophyllous Foliage Leaves
must produce more sugar by photosynthesis
limits sclerenchyma in foliage leaves
soft, flexible, edible
some leave for few years
leaves harden
resistant to animals, fungi, freezing temp. UV light
these plants are sclerophyllous
leaves are sclerophylls
has sclerenchyma
Thick cuticle, abundant wax
Leaves of Conifers
leaves are sclerophylls
thick cuticle
epidermis and hypodermis cells have thick walls
always simple, never compound :warning:
needles
cypresses
thuja
mostly perennial
shed each autumn
Larix
Taxodium
Metasequoia
Bud Scales
protect from low temp. and cold, dry wind of winter
only protection, NO PHOTOSYNTHESIS
tougher and waxier than regular leaves
thin layer of corky bark
petiole is short or absent
small and rarely compound
tight layer around stem tip
Spines
Cacti
2 types of leaves
green cactus has microscopic green leaves
plus cluster of axillary bud
cactus spines -- modified leaves of axillary buds
protective
has good water
No mesophyll parenchyma or vscular tissue
only tightly packed fibers
Tendrils
peas
cucumbers
squash
another form of modified leaf
grows indefinitely
contain cells -- capable of sensing contact with an object
when it touches something, stops growing
other side continues to elongate
grows around
Leaves with Kranz Anatomy
C4 photosynthesis
lack palisade parenchyma and spongy mesophyll
has bundle sheath of large chlorophyllous cells
mesophyll cells surrounds sheath
Insect Traps
insectivory
obtain nitrogen by digesting
need for amino acid
active or passive traps
Active - move
Drosera
passive - immobile
Nepenthes, Darlintonia, Sarracenia
habitats poor in nitrates and ammonia
internal structure of Foliage Leaves
Epidermis
large surface area; water can be lost
transpiration
ALLOW CO2 ENTRY
reasonably waterproof but transluent
stem and leaf epidermis are similar
flat, tabular, ordinary epidermal cells
guard cells and trickomes
may be abundant
dorsiventral
different microclimates on both ends
no stomata at the upper epi. in most
most stomata in the lower epidermis
beneficial
only few fungi can get in
contains crypts
water can enter
hair + trichomes
upper: provides shade
lower: rapid air movement + slow water loss
coating of cutin + wax on outer walls
retains water
Mesophyll
ground tissues interior to epidermis
palisade parenchyma
aka palisade mesophyll
main photosynthetic tissue of most plants
separated slightly
intercellular space
CO2 dissolve into cytoplasm
maximum absorption of light and photosynthesis
spongy mesophyll
lower portion
open, loose aerenchyma
permits CO2
from stomata to other parts
Vascular tissues
between palisade parenchyma and spongy mesophyll
Eudiocot
usually one large mid-rib
lateral veins
minor veins
important for releasing water from xylem
loading sugar from phloem
site of material exchange
no fibers/nonconducting cell
ending: only xylem
midrib/lateral vein
they always contain primary xylem and primary phloem
conduction
bundle sheath (fibers)
around vascular tissue
difficult for insects to chew
bundle sheath extension
mass of fibers
rigidity to blade
some means by which water moves
Petiole
tiny but massive in plants
palms, rhubarb, celery, water lilies
transition b/w stem and the lamina
tissue arrangement differs
epidermis may be similar
petiole mesophyll is like cortex
leaf traces
branch from stem vascular bundle
remain distinct or fuse together
spitules
two flaps of tissues
protect shoot apical meristem
when leaf is young
large enough to contribute photosynthesis
Concepts
photosynthesis :recycle:
ADVANTAGES
Protection
bud scales
spines
support
tendrils
storage
fleshy leaves of bulbs
bud scales leaves are different than those of foliage leaves
shoot system
stems and leaves
function together to survive
leaves
flat and thin
maximum light absorption + CO2
tissues must be alive
chlorophyll-rich chlorenchyma
carry out photosynthesis
stems
elevate leaves
conduct materials to/from them
cylindrical stem
maximum conduction and support
most of the stem must be dead
to be functional
division of labor
integration of distinct plant organ
External Structure of Foliage Leaves
obvious function --> photosynthesis
photosynthesis
absorbs CO2
use light
makes crabohydrate
IMPORTANT
:forbidden: lose excessive water
:forbidden:fungi, bacteria, epifoliar algae
:forbidden:nutritious and delicious
:forbidden: effective sail
CHEAP
fails in any category below, plant dies
Parts
leaf blade (lamina)
harvests light
simple or compound
simple: one part
large blade could be teared up :warning:
compound: divided into several individual parts
leaflets
petiolule
rachis
dorsal surface (abaxial side)
#
below the blade
larger veins; backbones
ventral surface (adaxial)
upper side
smooth
petiole (stalk)
hold blade in light
prevents shades
leaves flutter in wind (thin petiole)
Sessile leaf
small/very long and narrow
self-shading, not problem
aeonium
deserts
sheathing leaf base
leaf base wraps around the stem
Veins or vascular tissue bundle
distribute water (stem-->leaf)
collect sugar (photosynthesis)
carry them to stems
eudicots and angiosperms
reticulate venation
monocots
long, strap-shaped leaves
larger (side by side), interconnections
parallel venation
abscission zone
leaf base (location)
perpendicular to petiole
cutting off the leaf when it's not useful anymore
leaf scar
protective scar tissue
monocots, ferns, cycads
Initiation and Development of Leaves
Basal Angiosperms and Eudicots
leaf primordium
protrusion from cells interior to protoderm
leaf protoderm and leaf ground meristem
as it grows, increases in thickness
meristematic
in compound leaf
2 rows of loci initiate leaflets
stomata, trichomes, and vascular bundles differentiate
become dormant after reaching development stage
Monocots
expansion of shoot apical meristem
forms leaf primordium
cells involve until primordium encircles apical meristem
sheathing leaf base + original conical leaf primordium
now on side of top of tube
in some, lamina becomes broad and expanded like eudicot
grasses, lilies, etc. have linear, strap-shaped leaves
protoxylem and protophloem are constantly stretched
vessel elements and sieve tube
