1. 2/17/2010
Ontogenetic development
STEM
Ontogenetic development
Arrangement of Primary tissues
Types of stem
Arrangement of primary tissues
A. aerial 1. Epidermis
2. Cortex
B. sub-aerial
3. Endodermis
C. underground 4. Stele
Nature of stem/ Texture
A. herbaceous
B. woody
1
2. 2/17/2010
Cortex Endodermis
Parenchyma (photosyn., storage) Delimits the cortex from the vascular
Collenchyma cylinder
Fibers Not usually developed in stems
Lacunate Conspicuous in vascular cryptogams
Sclereids, laticifers, secretory cells + Lignin and suberin along radial and
transverse walls
Maturation: suberin lamellae on the entire
inner surface of the walls + cellulose +
lignin
Starch sheath Primary vascular system
Young eudicot stems
Homologous to endodermis
Vascular bundle Continous
2
3. 2/17/2010
Vascular bundle Vascular bundle
Amphivasal Amphicribral
-- some monocots -- Pteridophytes
collateral bicollateral -- Aloe, Agavaceae
CONCENTRIC
Vascular bundle Stele
Closed Anything inside the endodermis
- without vascular cambium Pericycle + vascular tissues + pith
Open
- With vascular cambium
Anomalous structures Types of stele
Medullary bundles Illustrates various stages of evolution of
Cortical bundles primary vascular system
A.
A Protostele
B. Siphonostele
3
5. 2/17/2010
Overlapping leaf gaps
Dictyostele Eustele Atactostele
--meristeles
What type of bundle?
Medullary rays Primary xylem differentiation
Not all interruptions are leaf gaps Endarch – differentation of metaxylem
Some result from reduction of vascular proceeds progressively towards the
tissue and formation of interfascicular periphery (centrifugal– order of
pa e c y a
parenchyma maturation))
Exarch
Mesarch
How about the phloem?
Anatomy of the node
Leaf trace
Leaf gap = “lacuna”
Classification (no. of leaf gaps/leaf)
(no
1. Unilacunar
2. Trilacunar -- primitive
3. Multilacunar
5
