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