B. Sc. III Botany

Dr. (Miss) Kalpana R. DatarAssistant Professor

DEPARTMENT OF BOTANY WILLINGDON COLLEGE, SANGLI.

kalpana_datar@yahoo.com

Stelar evolution

Stelar Evolution

• Stele is unit of vascular system.

• The tissues internal to the endodermis

is stele.

• It includes Xylem, phloem and cells of

the ground tissue that is pericycle, pith

and medullary rays.

Protostele• Solid core of xylem is in the centre.

• Xylem is surrounded by phloem, pericycle and endodermis.

• It is simplest and primitive type of stele.

• It is divided into four types

Haplostele 1.It is a type of protostele.2.Smooth core of xylem is present in the center.3.It is surrounded by phloem, pericycle and endodermis3.It is the most primitive type of protostele.E.g. Lygodium,

Selaginella krausiana

Actinostele1.It is a type of protostele.

2. xylem is star shaped

and present in the center.

3. It is surrounded by

phloem, pericycle and

endodermis.

Eg. Psilotum

1.It is a type of protostele.

2. xylem is in the form

of parallel plates in the

center.

3.It is surrounded by

phloem, pericycle and

endodermisE.g. Lycopodium clavatum

Plectostele

Mixed Protostele

1.It is a type of proto-

stele.

2. xylem and phloem

patches are uniformly

distributed in the center.

3.It is surrounded by

pericycle and endodermis.

E.g. Lycopodium cernum

Siphonostele1.Those steles which possesses parenchymatous

pith in the centre of the stele are known as

Siphonostele.

2.They are also called Hollow or tubular steles.

3.There are two types.

i. Amphiphloic Siphonostele

ii. Ectophloic Siphonostele

1.The xylem is surrounded both outside and inside by phloem, pericycle and endodermis.

2. Pith is present in thecentre.

E.g. Marsilea

AmphiphloicSiphonostele

Ectophloic Siphonostele 1.The xylem is surrounded by phloem, pericycle and endodermis on the outside only.2.Pith is present in the centre.3. It is more highly evolved than AmphiphloicSiphonostele

E.g. Fern- Osmunda

Dictyostele1.Leaves are produced on the stem. Xylem and

phloem from the main axis are supplied to leaves.

2.The patch of xylem and phloem which goes to

supply the leaf is known as Leaf trace.

3.Due to leaf trace a gap is left in the continuous

strand of xylem and phloem. The gap is known as

Leaf gap or Foliar gap.4.Siphonostele dissected by single leaf gap is

known as Solenostele.

Solenostele

Leaf gap

Dictyostele 1.When there are many leaf gaps in the stele, it is known as Dictyostele.

Eg. Fern- Asplenium

1. It is special kind of Siphonostele.2.The vascular tissue is separated into a

number of collateral vascular bundles.3.Parenchymatous tissue (Medullary ray)is

present in between the vascular bundles.4.Vascular bundles are arranged in the ring.5.Vascular cylinder is surrounded by pericycle

and endodermis.6.It is most highly evolved type of stele.7.It is found in gymnosperms and Dicotyledons.8.E.g. Sunfower stem, Cycas stem

Eustele-

Eustele:

1.In this type of stele vascular bundles arescattered in the ground tissue.

2.Vascular bundles are surrounded bypericycle and endodermis.

3. It is found in Monocotyledons. E.g. Maizestem

Atactostele-

1.Protostele is most primitive

type of stele.

2.All other types have been

evolved from it.

3.Eustele is most evolved type

of stele.