b. sc. iii botanywillingdoncollege.in/pdf/studymaterial/botany/stelar_evolution.pdf · stelar...
TRANSCRIPT
B. Sc. III Botany
Dr. (Miss) Kalpana R. DatarAssistant Professor
DEPARTMENT OF BOTANY WILLINGDON COLLEGE, SANGLI.
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.