Stems - I. Primary Structure of Stems Dermal – Epidermis Ground Tissue –Cortex –Pith –Other...
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Transcript of Stems - I. Primary Structure of Stems Dermal – Epidermis Ground Tissue –Cortex –Pith –Other...
Stems - I
Primary Structure of Stems
• Dermal – Epidermis• Ground Tissue
– Cortex– Pith– Other
• Vascular Tissue – vascular bundles– Collateral VB– Bicollateral VB– Concentric VB
Acorus stem with endodermis
Amphivasal VB
Morphological concepts used to explain primary anatomy
• Stelar Theory
• Leaf Trace Theory
Types of steles
Protosteles -------------->
Siphonosteles-------------->
Protosteles have a central core of vascular tissue surrounded by cortex (not shown)
Xylem
Phloem
Haplostele in Psilotum rhizome
Haplostele in Selaginella root
Actinostele in Psilotum stem
Actinostele in Ranunculus root
Plectosteles in Lycopodium stems
Siphonosteles have a central pith surrounded by a cylinder of vascular tissue
Ectophloic Siphonostele
Amphiphloic siphonostele
Dictyostele
Ectophloic siphonstele in fern rhizome with a ring of xylem surrounded by a ring of phloem
Amphiphloic siphonostele in a fern rhizome with two rings of phloem on each side of xylem
Leaf traces and leaf gaps
Siphonostele with a leaf gap and leaf trace
Dictyosteles are considered amphiphloic siphonosteles with overlapping leaf gaps
Modified siphonosteles
Eustele
Dicots and gymnosperms Monocots
Evolution of stelar types
Flattened protostele in Selaginella stem
Flattened haplostele? OR Actinostele with two arms?
Actinostele with irregular shape
Or a plectostele with connections between xylem areas?
Stele in stem Asteroxylon (fossil member of Division Lycophyta)
Leaf traces originate at the apical meristem
Leaf traces
Anatomy of nodes
Unilacunar with 2 traces
Unilacunar with 1 trace
Trilacunar with 3 traces
Multilacunar with many gaps and many traces