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 gymnospermsMonocots

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