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Chapter 6 (External Structure of Foliage leaves (light harvesting portion…
Chapter 6
External Structure of Foliage leaves
Leaves are the most obvious form of external foliage
a leaf blade can be simple or compound
a simple leaf blade has a blade of one part
a compound leaf blade has a blade divided into several individual parts
a compound leaf has multiple small blades called leaflets
during photosynthesis leaves absorb carbon dioxide
best for leaves to be flat and wide
light harvesting portion of the leaf is called the leaf blade or the lamina
the blades lower surface is called the dorsal surface
the upper side is called the ventral surface
most leaves have a stalk called a petiole that holds the blade in the light
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long, thin petioles allow the leaf to flutter
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flutter can sometimes knock insects off the leaf
small self shading leaves with no petiole are called a sessile leaf instead of a petiolate
when the leaf base wraps around the stem it forms a sheathing leaf base
the abscision zone is oriented perpendicular to the petiole
within a leaf are veins of vascular tissue
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Morphology and anatomy of other leaf types
succulent leaves
numerous adaptations allow plants to survive in the desert one being succulent leaves
the mesophyll takes up littele air space
sclerophyllous foliage leaves
with the prolonged lifetime that these leafs have, they have more resilience to animals, freezing, fungi, and ultraviolet light
cuticle is very thick
leaves of conifers
conifer leaves are always simple and never compound
conifer leaves are perennial
Tendrils
another form of modified leaf
Bud scales
one of the most common types of modification to leaves is bud scales
differs from that of foliage leaves
Spines
cacti have two types of leaves
cactus spines are modified leaves of auxiliary buds
Internal structure of foliage leaves
epidermis
flat thin leaves have many openings which can lose water
water loss through the epidermis is called transpiration
stomata help regulate gas exchange and also help prevent water loss
mesophyll
ground tissues interior of the epidermis is called mesophyll
the upper level of the cells are paliside parenchyma cells
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the lower level is the spongy mesophyll
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vascular tissue
between the upper and lower levels are vascular tissue
a euidicot usually has a large mid-rib
these branch off into smaller veins known as lateral veins and then mirror veins
many fibers form to create a bundle sheath
veins, often the larger ones, have a mass of fibers above, below, or both called the bundle sheath extension
petiole
usually tiny but in some species they are massive
vascular tissue are the most variable bundles or 1, 3, or 5 are called leaf traces
bears two small flaps of tissue at the base called stipules
initiation and development of leaves
leaves are only grown by shoots of the apical meristem
at the base of the meristem calls just to the interior of the protoderm grow outward forming a lead primordium
Monocots
initiated by shoots of the apical meristem
in some monocots the lamina becomes broad and expanded
in many perennial plants, leaves are initiated in the summer
