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Leaves (External Structures of Foliage Leaves (functions (photosynthesis,…
Leaves
External Structures of Foliage Leaves
functions
photosynthesis
part of the leafs functions can interfere with this process
water proof
pathogen resistant
absorb light energy to convert CO2 to carbs
leaf flat and wide for maximum absorption of light
light only penetrates a short distance
leaves thin to allow chlorophyll to absorb light
light absorbing side = leaf blade/ lamina
smooth, and ventral surface
underside = dorsal surface
larger veins seen
water retention
protection against foreign invaders
provide nutrients to animals
not cost that many carbs in making
petiole
stalk that holds leaf into the light
prevents shading from leaves above
consequences
long, thin, flexible allows leaves to flutter in wind
makes it hard for maximum CO2 absorption
does however provide protection from insects
sessile leaf
leaves are small or very long and narrow
self shading is not a problem
monocots
grasses, irises, lilies, agaves
long and tapered
self shading occurs at the base
most is exposed to light
lack a petiole
form a sheathing leaf base
simple or compound
simple= has a blade or just one part
compound= blade divided into several parts
many blades/leaflets
allows for turbulence over leaves in a breeze
CO2 brought in more and heat reduced
allows for protection against invaders
leaves act as barriers
also if pathogen affects one, the effected dies and carries pathogen way
never bear buds, or have terminal buds
attached by a petiolue to an extension of the petiole, the rachis
shapes
tremendous variety of shapes and sizes
biologists believe all function so well, that no distinct shape or size is better then the other
some plants may even have more then one type of leaves
useful tool to identify plants
veins
bundles of vascular tissue
distribute water
collect sugars
basal angiosperms = reticulate venation
monocots= parallel venation
Morphology and Anatomy of Other Leaf Types
Succulent Leaves
adaptation to surviving in the desert
thick and fleshy
mesophyll contains very few air spaces
transparent for light absorption
shapes that favor water conservation
cylindrical or spherical
consequence of reducing capacity for CO2 uptake
Crassulacea
,
Portulacaeae
, and
Aizoaceae
Sclerophyllous Foliage leaves
Extended lifetime, and prolonged productivity
feasible
hardness
due to high amount of sclerenchyma
just below epidermis
epidermis is also thick
very thick cuticle with waxes
resistant to animals, fungi, cold, and UV light
barberry, holly,
Agave
, and
Yucca
leaves of Conifers
leaves are sclerophylls
thick cuticle, and thickened cell walls on epidermis and hypodermis
contain unpalatable chemicals
leaves are simple, and never compound
forms
needles
scale-like leaves form shield like cover on stems
mainly perennial
remain on the stem for year
evergreens
Bud Scales
protect shoot apical meristems that are dormant
low temps
drying action of wind
form tight layer around stem tip
tougher and waxier
no photosynthesis
gives different structure then foliage leaves
Spines
Cacti
axillary buds modified
protection
no mesophyll parenchyma or vascular tissue present
mesophylll= closely packed fibers
lignin deposited to walls after maturation
cells die and dry out
Tendrils
modified leaf of peas, cucumbers, and squash
contain cells that are capable of sensing contact with an object
uses object as support as it coils around
Kranz Anatomy
C4 photosynthesis
lack palisade and spongy mesophyll
contain prominent bundle sheaths with large chlorophyllous cells
sheaths covered in mesophyll cells that come from vascular bundle
gives plant a mechanism of CO2 transport
plants adapt to arid environment
Insect Traps
ability to trap and digest insects
gain nutrients and chemicals needed
plants that grow in low nitrogen and ammonia
active or passive
active= moves
Drosera
upper surface covered in glandular trichomes that secrete sticky digestive enzymes
leaf curls around captured victim
Venus Flytrap
passive= no movement
Nepenthes
,
Darlingtonia
, and
Sarracenia
lamina is tubular and secretes watery digestive enzyme and contains trichomes
Internal Structures of Foliage Leaves
Epidermis
waterproof
loss of H2O= transpiration
translucent, and allows entry of CO2
cells
large amount of flat, tabular, ordinary epidermal cells
epidermal have a layer of cutin
aids in retention of water
digestion by fungi difficult
smooth surface prevents sticking
guard cells and trichomes
upper and lower parts
upper
low amount of stomata
lower
high number of stomata
allows for better water retention
protection against invaders
often hairy and covered in trichomes
can provide shade on upper part
lower
prevent rapid air movement and slow water loss
make difficult for walking or chewing for predators
may even sting
Mesophyll
ground tissues interior to leaf epidermis
palisade parenchyma
upper layer of cells
most photosynthetic tissue of plants
one cell layer thick
cells separated slightly to expose each to the intracellular spaces
large surface maximum dissolution of CO2
Spongy mesophyll
lower portion
loose aerenchyma that permits CO2 to diffuse rapidly from stomata to all parts of the leaf's interior
Vascular Tissues
between palisade and spongy mesophyll
eudicot= 1 large midrib/midvein
lateral veins branch into narrow minor veins
minor release water from xylem and load sugar into phloem
site of material exchange
contain no fibers, or other nonconducting cells
lateral/midrib used in conduction
contain both primary xylem on upper and phloem on under
fibers arranged as a bundle sheath around vascular tissues
protection
other cells: mucilage, tannin, or starch could be present
Petiole
may be tiny or massive depending on the plant
palms= massive
transition from stem and lamina
mesophyll is like the cortex
not compact, and aerenchymous
collenchyma present for support
vascular tissue is the most variable
multiple vascular bundles
=leaf traces
may branch further or fuse with one another
arranged in many patterns
most fuse into the midvein
stipules
two flaps of flesh
protect apical meristem
photosynthesis in some plants
Initiation and Development of Leaves
Basal Angiosperms and Eudicots
leaves produced through activity of apical meristem
leaf primordium at the base
protrusion that extends upward as a cone
increases in thickness forming bulk of midrib
growing outward forms forms lamina
lamina extension aloows stomata, trichomes, and vascular bundles to differentiate
becomes taller then apical
consists of leaf protoderm and ground meristem
cells are meristematic, have dense cytoplasm, amd small vacuoles
cells in middle differentiate into provascular tissue and then into xylem and phloem bundles
perennial plants
leaves initiated in the summer or autumn before they mature
become dormant and part of a resting terminal/axillary bud
next growth period the bud opens and leaves expand as vacuoles fill with water
little mitosis, only cell maturation
Monocots
Initated by expansion of apical meristem that forms leaf primordium
cells adjacent grow upward along with it
cylinder soon encircles shoot apical meristem
conical leaf primordium gives rise to lamina
cells stay active mitotically
extends leaf
shoot apex enlarges, forms new tissues, and initiates next leaf primordium
sheathing base
