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Tissue & Primary Growth of Stems (Internal Organization of Stems…
Tissue & Primary Growth of Stems
Development of Land Plants
Plant bodies
Primary plant body
Herbaceous
Secondary plant body
Woody
Herbs
Three basic parts
Stems
Roots
Leaves
Modified by natural selection
Angiosperms
Three groups
Eudicots
Broadleaf plants
Monocots
Basal angiosperms
Basic Cell & Tissue Types
Collenchyma
Unevenly thick primary walls
Plasticity
Elongating shoot tips
Sclerenchyma
Primary & secondary walls
Provides elastic support
Water transport (some)
Two types
Mechanical
Sclereids
Short
Fibers
Long
Conducting
Tracheids
Vascular plants
Vessel elements
Flowering plants
Parenchyma
Function of parenchyma cells
Parenchyma tissue
Only thin primary walls
All soft plant parts
80 to 100 nm thick
Phloem
Numerous subtypes
Chlorenchyma cells
Photosynthesis
Glandular cells
Secretion
Transfer cells
Transport of materials
External Organization of Stems
Nodes
Leaf axil
Region just above node
Axillary bud
Bud scales
Terminal bud
Internodes
Regions between nodes
Shoots
Bulbs
Short shoots
Thick, fleshy leaves
Ex. onion
Corms
Vertical thick stems
Thin, papery leaves
Ex. gladiolus
Rhizomes
Fleshy horizontal stems
Plant grows underground
Ex. bamboo
Tubers
Horizontal stems
Short growth periods
Storage of nutrients
Ex. potatoes
Phyllotaxy (leaf arrangement)
Decussate
4 rows of leaves
Whorled
3+ leaves per node
Opposite
2 leaves per node
Spiral
Spiral of leaves
Alternative
1 leaf per node
Distichous
2 rows of leaves
Internal Organization of Stems
Epidermis
Cuticle
Outer wall with cutin
Water impermeable
Layer of parenchyma cells
External interchange of material
Prevention of water loss
Protection: invasion barrier
Stoma
Guard cells
Stomatal pores
Trichomes (hairs)
Elongated epidermal cells
Protection
Secretion
Vascular tissues
Xylem
Composed of sclerenchyma cells
Tracheids
Long/narrow
Pointed ends
Pit membrane
Tracheary element
Secondary cell walls
Scalariform thickening
Annular thickenings
Reticulate thickening
Cirular bordered pits
Helical thickening
Pits/Pit pairs
Water transport
Dead at maturity
Vessel elements
Short/wide
Flat ends
Perforation
Only in flowering plants
Phloem
Type of parenchyma tissue
Sieve cells
Long/narrow
Pointed ends
Albuminous cells
Sieve tube members
Short/wide
Flat ends
Sieve tube
Sieve plates
Companion cells
Sieve element
Sieve pores
Sieve areas
Alive at maturity
Cortex
Interior to epidermis
Photosynthetic parenchyma
Some collenchyma
Sometimes secretion cells
Aerenchyma in fleshy stems
Vascular Bundles
Xylem and phloem together
Collateral
Primary xylem
Primary phloem
Arrangement
Eudicots/angiosperms: piths
Monocots: "scattered" bundles
Stem Growth & Differentiation
Developing cell tissue types
Provascular tissue
Young xylem/phloem cells
Ground meristem
Early pith and cortex
Protoderm
Epidermal cells
Apical meristem
Cell division
Subapical meristem
Metaxylem
Grow longest
Any secondary wall type
Protophloem
Short life span
Small, no companion cells
Protoxylem
Differentiate first
Annular or helical secondary walls
Metaphloem
Longer life spans
Large with companions cells
