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Leaves (External Structures of Foliage Leaves (Petiole (stalk (holds…
Leaves
External Structures of Foliage Leaves
Most obvious function is for Photosynthesis
Lamina (leaf blade)
Flat, light harvesting portion of the leaf
dorsal surface (lower side)
Large veins protrude like backbones
Ventral Surface (top side)
usually smooth
Petiole
stalk
holds leaves into light
long, thin, flexable
No need for one if the leaf is small
helps prevent self shading
Simple leaf
blade has just one part
Compound leaf
blade is divided into several individual parts
has leaflets
many small leafs
Veins
Bundles of vascular tissues
Sessile leaf
does not need a petiole
Morphology and Anatomy of Other Leaf Types
Succulent Leaves
thick/fleshy leaves
surface-to-volume ration
favors water conservation
advantageous for water retention
automatic consequences of reducing the amount of CO2
Sclerophyllous Foliage Leaves
Must produce more sugars by photosynthesis
or will lose energy every time it produced a leaf
leaves tend to be soft, flexible, and edible
Leaves of Conifers
leaves are sclerophylls
thick cuticle
epidermis and hypodermis cells have thick walls
simple leaves
mostly perennial
remain on stem for years
needles either short or longer
live for atleast 5 years
Bud Scales
most common modification to leaves
tight layer around the stem tip
primary role is protection
small
rarely compound
short/absent petiole
tougher and waxier than regular leaves.
frequently produce thin layer of corky bark
Spines
Clusters of spines
needle shaped but bladless
modified leaves of axillary buds
protection against hebivores
Tendrils
grow indefinitely
has cells that are capable of sensing contact with an object
when touched it causes it to quit growing a coil around the object
use it for support
Leaves with Kranz Anatomy
lack palisade parenchyma
lack mesophyll
adapts C4 plants to arid enviroments
Insect Traps
ability to trap/digest insects
grow in habitats low in nitrates and ammonia
leaves similar to foliage leaves
thin
capable of phoytosyntesis
lamina is tubular not flat
secretes watery digestive fluid
some produces sticky digestive liquid
Internal Structures of Foliage Leaves
Epidermis
outer layer of the leaf
Covered in a cuticle
Wax like structure to help hold water in the plant
absorbs water and minerals
regulates gas exchange
Mesophyll
lower part of the leaf
Allows CO2 to enter rapidly
Palisade Parenchyma
upper layer of cells found in a leaf
also called palisade meophyll
Some plants have this along both surfaces of the leaf
Example: Grass
Ground tissue interior to leaf epidermis
Petiole
Leaf Traces
1,3,5, or more vascular bundles
Stipules
found at base
can help protect the apical meristem
transition to the lamina
helps the shedding of leaves
Vascular Tissue
Mid Rib
Also known as mid vein
provides support
Lateral veins
emerge from Midvein
minor vein
emerge from lateral veins
are super narrow
Bundle Sheath
Fibers arranged as a sheath
Bundle Sheath extensions
Mass of fiber above, below, or both around large veins
give rigidity to the blade
Provides another way for water to move from the bundle out to the mesophyll
Initiation and Development of Leaves
Basal Angiosperms and Eudicots
Leaves only produced through the activity of a shoot apical meriste
Leaf Peimoridium
cells interior to the protoderm grow outward, forming a protrusion.
as it grows up it increases in thickness
Monocot
expansion of shoot apical meristem
forms Leaf primordium
grow upward forming primordium
gives a hood like shape
involves unitl primordium is a cylinder
or until it completely encircles the apical meristem
