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Tissues and the Primary Growth of Stems (Internal Organization of Stems:…
Tissues and the Primary Growth of Stems
Basic Types of Cells and Tissues
Parenchyma
Have primary thin walls
Parenchyma tissue:
Mass of parenchyma cells
Collenchyma
Primary thin wall
Becomes thickened in corners
Absorbs water
Sclerenchyma
Primary wall
Thick secondary wall
Almost always lignified
Elastic walls
Absorbs water
Conducting sclerenchyma
Mechanical sclerenchyma
External Organization of Stems
Nodes
Leaves are attached
Internodes
Regions between the nodes
Leaf axis
Above where leaf attaches
Stem area
Axillary bud
Miniature shoot with:
Dormant apical meristem
Several young leaves
Covered by bud scales
Modified leaves
Protect organs inside
Terminal bud
Extreme tip of stem
Phyllotaxy
Arrangement of leaves on stem
Internal Organization of Stems: Arrangement of Primary Tissues
Epidermis
The outermost surface of an herbaceous stem
single layer of living parenchyma cells
Cutin
Fatty substance
Makes wall impermeable to water
Cuticle
Cutin build up
Stoma:
Guard cells
Stomatal pore
Cortex
Interior to the Epidermis
Vascular Tissues
2 types:
Xylem
Conducts water & minerals
Pholem
Distributes sugars & minerals
Xylem
Tracheids
Vessel elements
Tracheary element
Refers to both cell types
Phloem
Sieve cells
Sieve tube members
Sieve element
Refers to both cell types
Vascular Bundles
Xylem & Phloem occur together
Interior to cortex
Pith
Region of parenchyma
Collateral
Xylem & Phloem run parallel
Stem Growth and Differentiation
Apical Meristems
Stems grow longer
Creating new cells at tips
Subapical Meristems
Region below apical meristems
Producing cells for region below
Protoxylem
Constitute first xylem to appear
Metaxylem
Largest tracheary elements of all
Protophloem
Exterior cells matured
Metaphloem
Cells closest to metaxylem
