botany basics 3 crop science 1 fall 2004 september 28, 2004
TRANSCRIPT
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Botany Basics 3Botany Basics 3
Crop Science 1Crop Science 1
Fall 2004Fall 2004
September 28, 2004September 28, 2004
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Leaf FunctionLeaf Function
Principal functionPrincipal function Photosynthesis Photosynthesis
to absorb sunlight to manufacture plant to absorb sunlight to manufacture plant sugarssugars
Surfaces flattened to present a large area Surfaces flattened to present a large area for efficient light absorptionfor efficient light absorption
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Leaf StructureLeaf Structure
BladeBlade expanded thin structure expanded thin structure
on either side of the on either side of the midrib and usually the midrib and usually the largest, most largest, most conspicuous part of a conspicuous part of a leafleaf
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Leaf StructureLeaf Structure
PetiolePetiole Stem-like appendage Stem-like appendage
which holds the leaf which holds the leaf away from the stem away from the stem
The base is attached The base is attached to the stem at a nodeto the stem at a node
Vary in length or may Vary in length or may be lacking entirely, in be lacking entirely, in which case the leaf which case the leaf blade is described as blade is described as sessile or stalklesssessile or stalkless
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Leaf StructureLeaf Structure
Leaf axilLeaf axil The node where a petiole The node where a petiole
meets a stemmeets a stem Contain axillary budsContain axillary buds
single buds or bud clusterssingle buds or bud clusters Either active or dormantEither active or dormant Will develop into stems or Will develop into stems or
leaves under the right leaves under the right conditionsconditions
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Leaf Blade StructureLeaf Blade Structure
A leaf A leaf blade is blade is composed composed of several of several layers layers
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EpidermisEpidermis
Layer of thick, tough cells on the top and Layer of thick, tough cells on the top and bottom bottom
Primary function is to protect the other Primary function is to protect the other layers of leaf tissuelayers of leaf tissue
The arrangement of epidermal cells The arrangement of epidermal cells determines the leaf's surface texturedetermines the leaf's surface texture
Some leaves have hairs (pubescence), Some leaves have hairs (pubescence), which are extensions of epidermal cellswhich are extensions of epidermal cells
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CuticleCuticle
Part of the epidermisPart of the epidermis Produces a waxy layer called cutinProduces a waxy layer called cutin
Protects the leaf from dehydration and disease Protects the leaf from dehydration and disease The amount of cutin on a leaf increases with The amount of cutin on a leaf increases with
increasing light intensityincreasing light intensity Move plants from shade into full sunlight gradually to allow Move plants from shade into full sunlight gradually to allow
the cutin layer to build up and protect the leaves from rapid the cutin layer to build up and protect the leaves from rapid water loss or sunscaldwater loss or sunscald
Repels waterRepels water Many pesticides contain a spray additive to help the Many pesticides contain a spray additive to help the
product adhere to, or penetrate, the cutin layer (surfactant)product adhere to, or penetrate, the cutin layer (surfactant)
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Guard CellsGuard Cells
Special epidermal cells Special epidermal cells Open and close in response to environmental Open and close in response to environmental
stimuli (changes in weather and light)stimuli (changes in weather and light) Conditions that cause a loss of water (high Conditions that cause a loss of water (high
temperature, low humidity), or the absence of light temperature, low humidity), or the absence of light stimulate guard cells to closestimulate guard cells to close
Regulate the passage of water, oxygen, and Regulate the passage of water, oxygen, and carbon dioxide into and out of the leaf through tiny carbon dioxide into and out of the leaf through tiny openings called stomataopenings called stomata
In most species, the majority of the stomata are In most species, the majority of the stomata are located on the underside of leaveslocated on the underside of leaves
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MesophyllMesophyll
Located between the upper and lower Located between the upper and lower epidermisepidermis
Divided into:Divided into: dense upper layer (palisade mesophyll) dense upper layer (palisade mesophyll) lower layer that contains lots of air space lower layer that contains lots of air space
(spongy mesophyll) (spongy mesophyll) Located within the mesophyll cells are Located within the mesophyll cells are
chloroplastschloroplasts Where photosynthesis takes placeWhere photosynthesis takes place
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Types of LeavesTypes of Leaves
There are many kinds of plant leaves: There are many kinds of plant leaves: FoliageFoliage Scale leavesScale leaves Seed leavesSeed leaves Spines and tendrilsSpines and tendrils Storage leavesStorage leaves BractsBracts
Modified Leaves
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FoliageFoliage
Most common and conspicuous leaves Most common and conspicuous leaves Primary location of photosynthesisPrimary location of photosynthesis
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Scale leavesScale leaves
CataphyllsCataphylls Found on rhizomes and budsFound on rhizomes and buds Enclose and protect rhizomes and budsEnclose and protect rhizomes and buds
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Seed leavesSeed leaves
CotyledonsCotyledons Found on embryonic plantsFound on embryonic plants Store food for the developing seedlingStore food for the developing seedling
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Spines and TendrilsSpines and Tendrils
Found on plants such as barberry and Found on plants such as barberry and pea plantspea plants
Protect a plantProtect a plant Help support stemsHelp support stems
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Storage LeavesStorage Leaves
Found on bulbous plants and succulents Found on bulbous plants and succulents Store foodStore food
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BractsBracts
Often are brightly colored Often are brightly colored The showy structures on dogwoods and The showy structures on dogwoods and
poinsettias are bracts, not petalspoinsettias are bracts, not petals
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VenationVenation
The vascular bundles of xylem and The vascular bundles of xylem and phloem extend from the stem, through phloem extend from the stem, through the petiole, and into the leaf blade as the petiole, and into the leaf blade as veins. veins.
The term venation refers to how veins The term venation refers to how veins are distributed in the blade. are distributed in the blade.
There are two principal types of venation: There are two principal types of venation: parallel-veined and net-veined parallel-veined and net-veined
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VenationVenation
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Parallel-Veined LeavesParallel-Veined Leaves
Numerous veins run essentially parallel to each Numerous veins run essentially parallel to each other and are connected laterally by minute, other and are connected laterally by minute, straight veinlets straight veinlets
Occur most often on monocotyledonous plants Occur most often on monocotyledonous plants The most common type of parallel veining is The most common type of parallel veining is
found in plants of the grass family, whose veins found in plants of the grass family, whose veins run from the leaf's base to its apexrun from the leaf's base to its apex
Another type of parallel venation is found in Another type of parallel venation is found in plants such as banana whose veins run plants such as banana whose veins run laterally from the midriblaterally from the midrib
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Net-Veined LeavesNet-Veined Leaves
Also called reticulate-veinedAlso called reticulate-veined Veins branch from the main rib or ribs Veins branch from the main rib or ribs
and subdivide into finer veinlets then and subdivide into finer veinlets then unite in a complicated networkunite in a complicated network
More resistant to tearing More resistant to tearing Occur on dicotyledonous plantsOccur on dicotyledonous plants
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Pinnate vs. PalmatePinnate vs. Palmate
Either Either PinnatePinnate
The veins extend laterally from the midrib to The veins extend laterally from the midrib to the edge the edge
Apples, cherries, and peachesApples, cherries, and peaches PalmatePalmate
The principal veins extend outward, like the The principal veins extend outward, like the ribs of a fan, from the base of the leaf blade ribs of a fan, from the base of the leaf blade
Grapes and maplesGrapes and maples
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Common Blade ShapesCommon Blade Shapes
LanceolateLanceolate Longer than wide and Longer than wide and
tapering toward the tapering toward the apex and baseapex and base
LinearLinear Narrow, several times Narrow, several times
longer than wide, and longer than wide, and of approximately the of approximately the same width same width throughoutthroughout
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Common Blade ShapesCommon Blade Shapes
Cordate Cordate Heart-shapedHeart-shaped Broadly ovate, Broadly ovate,
tapering to an acute tapering to an acute apex, with the base apex, with the base turning in and forming turning in and forming a notch where the a notch where the petiole is attachedpetiole is attached
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Common Blade ShapesCommon Blade Shapes
EllipticalElliptical About two or three About two or three
times as long as wide, times as long as wide, tapering to an acute tapering to an acute or rounded apex and or rounded apex and basebase
OvateOvate Egg-shaped, basal Egg-shaped, basal
portion wide, tapering portion wide, tapering toward the apextoward the apex
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Common Margin FormsCommon Margin Forms
EntireEntire Smooth edge with no Smooth edge with no
teeth or notchesteeth or notches
CrenateCrenate Rounded teethRounded teeth
DentateDentate Teeth ending in an Teeth ending in an
acute angle pointing acute angle pointing outwardoutward
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Common Margin FormsCommon Margin Forms
SerrateSerrate Small, sharp teeth Small, sharp teeth
pointing toward the pointing toward the apexapex
IncisedIncised Sharp, deep, irregular Sharp, deep, irregular
teeth or incisionsteeth or incisions Lobed Lobed
Incisions that extend Incisions that extend less than halfway to less than halfway to the midribthe midrib
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Common Apex ShapesCommon Apex Shapes
AcuteAcute Ending in an acute Ending in an acute
angle, with a sharp, angle, with a sharp, but not acuminate, but not acuminate, pointpoint
AcuminateAcuminate Tapering to a long, Tapering to a long,
narrow pointnarrow point ObtuseObtuse
Tapering to a rounded Tapering to a rounded edgeedge
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Common Base ShapesCommon Base Shapes
CuneateCuneate Wedge-shaped; Wedge-shaped;
triangular with the triangular with the narrow end at the narrow end at the point of attachmentpoint of attachment
ObtuseObtuse Tapering to a rounded Tapering to a rounded
edgeedge CordateCordate
Turning in and Turning in and forming a notchforming a notch
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Plant IdentificationPlant Identification
Leaves are useful for plant identification: Leaves are useful for plant identification: Leaf's venationLeaf's venation Blade and margin shapesBlade and margin shapes Apex and base shape Apex and base shape Leaf type Leaf type Leaf arrangementLeaf arrangement
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Leaf TypeLeaf Type
Simple leavesSimple leaves Leaf blade is a single, Leaf blade is a single,
continuous unitcontinuous unit Compound leavesCompound leaves
Composed of several Composed of several separate leaflets arising from separate leaflets arising from the same petiolethe same petiole
Some leaves are doubly Some leaves are doubly compoundcompound
Leaf type can be confusing, Leaf type can be confusing, because a deeply lobed because a deeply lobed simple leaf may look like a simple leaf may look like a compound leafcompound leaf
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Leaf ArrangementLeaf Arrangement
OppositeOpposite Positioned across the Positioned across the
stem from each other, stem from each other, with two leaves at with two leaves at each nodeeach node
Alternate (spiral) Alternate (spiral) Leaves are arranged Leaves are arranged
in alternate steps in alternate steps along the stem, with along the stem, with only one leaf at each only one leaf at each nodenode
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Leaf ArrangementLeaf Arrangement
WhorledWhorled Arranged in circles Arranged in circles
along the stemalong the stem
RosulateRosulate Arranged in a rosette Arranged in a rosette
around a stem with around a stem with extremely short nodesextremely short nodes
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Leaves as FoodLeaves as Food
Leaf bladeLeaf blade Chives, collards, dandelions, endives, kale, Chives, collards, dandelions, endives, kale,
leaf lettuce, mustard, parsley, spinach and leaf lettuce, mustard, parsley, spinach and Swiss chardSwiss chard
Cluster of fleshy leaf basesCluster of fleshy leaf bases Leeks, onions, and Florence fennelLeeks, onions, and Florence fennel
Petiole Petiole Celery and rhubarbCelery and rhubarb