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Tissues and the Primary Growth of Stems (External organization of Stems…
Tissues and the Primary Growth of Stems
Concepts
secondary plant body
Woody body
Oaks
Magnolias
Roses
Boxwood
Maple
Covered with bark
Secondary tissues
Derived from meristems other than apical meristems
Primary plant body
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Herbaceous body
Herb
Never becomes woody
Never covered with bark
Snapdragons
Corn
Wheat
Primary tissues
Derived from shoot and root apical meristems
Basal Angiosperms
Eudicots
Broad leaf plants
Maple
Asters
Roses
Monocots
Grasses
Lilies
Cattails
Palms
Basic parts of plant
Leaves
Root
Stem
Basic Types of Cells and Tissues
Collenchyma
Primary walls
Thick walls
Thin walls
Exhibits plasticity
Ability to retained new shape under pressure
Even if pressure is no longer present
Present in elongated shoot tips
Must be flexible
Must be long
It is the layer just under the epidermis
Require more glucose for production
Produced in shoot tips and young petioles
Need for extra strength justifies metabolic cost
Can absorb H2O
Sclerenchyma
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Contains primary and secondary walls
Walls are elastic
Can be deformed and returned to original shape
Develop from parenchyma cells
In mature organs
After they have achieved proper size/shape
After they have stopped growing
Support plant by strength alone
Remain upright
Do not droop
Strong enough to prevent protoplast from expanding
Unusable for growing shoot tips
Prevents further shoot elongation
Parenchyma
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Only thin primary walls
Most common type of cell
Consists of all soft parts of plant
Fruits
Petals
Leaves
Seeds
Metabolically active
Numerous sub-types of are specialized
Grandular Cells
Secrete nectar, fragrances, resins, mucilage, and oils
Typically contain few chloroplasts
Elevated amounts of dictyosomes and ER
Transport large amounts of sugar and minerals
Transfer Cells
Mediate short distance transport
Through large and extensive plasma membrane
Capable of housing numerous molecular pumps
Chlorenchyma Cells
Involved in photosynthesis
contain numerous chloroplasts
Thin walls allow light and CO2
Can absorb H2O
External organization of Stems
Internodes
Region between nodes
Leaf Axil
Part of the stem
Just above leaf attachment
Nodes
Attachment of leaves
Axillary Bud
Dormant apical meristem
Floral bud
Grow into flower
Grow into group of flowers
Vegetative bud
Grow into branch
No flowers present
Miniature shoot
Bud Scales
Small, Corky, and waxy
Protect delicate inside organs
Terminal Bud
Extreme tip of each stem
Leaf scars occur where leaves were attached
Phyllotaxy
Arrangement of leaves on stem
Decussate
Leaves located in four rows
Occurs in some species with opposite leaves
Whorled
Three or more leaves per node
Opposite
Leaves two per node
Spiral
Leaves not aligned with neighbors
Located slightly to side of neighbors
Must be above or below meighbors
Form spiral up the stem
Most common type of arrangement
May include alternate, opposite, or whorled leaves
Alternate
Leaves one per node
Alternate up the stem
Distichous
Leaves located in two rows only
Corn
Irises
Stolons
Also called Runners
Internodes are long and thin
Leaves do not expand
Can extend greatly without using plant nutrients
Rhizomes
Freshly horizontal stems
Allow plant to spread underground
Bamboo
Irises
Cannalilies
Tubers
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Horizontal Stems
Similar to Rhizomes
Grow only for short period
Means of storing nutrients
Meaning of word "Tuber"
Any bulky underground plant organ
Trunk
Allows plant to reach brighter light
May be advantageous in shady environments
Growth of vertical main shoot
Internal organization of Stems: Arrangement of Primary Tissues
Cortex
Next interior layer to epidermis
Typically Simple and homogeneous
Composed of
Photosynthetic parenchyma cells
Sometimes collenchyma cells
When complex may contain specialized cells that secrete:
Latex
Mucilage
Pitch (Resin)
Vascular Tissues
Xylem
Consists of Xylem, minerals, and phloem
Phloem
Distributes sugars and minerals
is not a circulatory system
Epidermis
Outermost surface if herbaceous stem
Single layer of parenchyma cells
More than than human epidermis
Human epidermis is much thicker
Human Epidermis consists of layers of dead cells
Environmental factors
Interchange of material
Between plant and environment occurs in epidermis
Functions of epidermis
Barrier against infection by bacteria
Shields internal cells from abrasions
By dust particles
By passing animals
By leaves
Reflectivity protects from overheating by sun
Xylem
Tracheids
Sclerenchyma cells
Tracheary elements
Shape of Tracheids
Long/narrow
Ends are pointed
Perforations
None
Secondary wall
Helical
Scalariform
Reticulate
Circular bordered pits
Annular
Vessel elements
Sclerenchyma cells
Tracheary elements
Secondary wall
Scalariform
Reticulate
Helical
Circular bordered pits
Annular
Perforations
Usually two
One in each end of wall
Terminal members with only one
Shape of vessel elements
Short/Wide
Ends usually flat
Phloem
Sieve cells
Shape
Long/Narrow
Ends are pointed
Sieve Areas
Small
Located over entire cell surface
Sieve element
Associated Cells
Albuminous Cells
Plant Division
All Non-angiosperm vascular plants
Sieve tube members
Sieve element
Shape
Short/Wide
Ends are usually flat
Sieve Areas
On side walls: Smalls
On end walls: large
end wall is sieve plate
Associated Cells
Companion cells
Plant Division
Angiosperms only
Vascular Bundles
Contains the xylem and phloem together
Located just interior to cortex
Basal angiosperm and Eudicots
Arranged in one ring surrounding pith
Monocots
Distributed as complex network
Bundles are throughout the inner part of the stem
All bundles are collateral
Primary xylem
Vascular bundle in xylem
Part of primary plant body
Primary phloem
Vascular bundle in phloem
Mixed with sieve elements
Mixed with companion cells
Mixed with albuminous cells
Stem Growth and Differentiation
Protophloem
Occurs in outer part of each vascular bundle
Exterior cells mature
Metaphloem
Occurs in outer part of each vascular bundle
Cell closest to metaxylem
Metaxylem
Longest time for growth before differentiation
Develop largest tracheary elements
Protoderm
Epidermal cells in early stages of differentiation
Protoxylem
Constitute the first xylem to appear
Cells around continue to grow and expand
Provascular Tissues
Young cells of xylem and phloem
Part of protoderm
Subapical Meristem
Region just below apical meristem
cells are dividing and growing
producing cells for the region below
Visable differentiation begins
Certain cells stop dividing
Certain cells start elgonating
Differentiate into tracheids and vessels elements
Contains ground meristem and protoderm
Ground Meristem
Equivalent stages of pith and cortex
Part of protoderm
Apical Meristem
Stems grow longer by creating new cells at tip
Producing progenitor cells for rest of stem
Cells divide by mitosis and cytokinesis
Parenchyma cells occur in the cortex
Sclerenchyma cells occur in the xylem
Similar in structure
Single layer of parenchyma cells in epidermis
Primary xylem contain primary plant body
