1. The document discusses the different types of steles (vascular tissue arrangements) found in plants, including protostele, siphonostele, solenostele, dictyostele, eustele, and atactostele.
2. It describes the evolution of different stele types, with protostele considered the most primitive form that evolved into more complex arrangements. Protostele evolved into actinostele and plectostele in some plants. The appearance of a pith led to the development of siphonosteles.
3. Stele evolution followed two main paths - development of ectophloic then solenostele siphonosteles, and development of
The slides has been edited. visit for new one on https://www.slideshare.net/alihaider408/stelar-system-stele-its-types-and-evolutionedited-182037813
Sorry for inconvenience.
Stele is defined as a central vascular cylinder, with or without pith and delimited the cortex by endodermis.
Van Tieghem and Douliot (1886) recognized only three types of steles.
1-Protostele
2-Siphonostele
3-Solenostele
Stelar Theory:
Major highlights of stellar theory are:
Stele is a real entity and present universally in all higher plants.
Cortex and stele are two fundamental parts of a shoot system
Stele and cortex are separated by endodermis
⢠Gymnosperms (Gymnos = naked, Sperma = seed) include the small group of plants with naked seeds.
⢠The Gymnosperms originated in the Devonian period of the Paleozoic Era and formed the supreme vegetation in the Mesozoic Era.
Gnetum: A Powerpoint Presentation on Gymnospemsshivduraigaran
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The Gymnosperms are a group of seed-producing plants (spermatophytes) that includes conifers (Pinophyta), cycads, Ginkgo, and gnetophytes. The term "gymnosperm" comes from the Greek composite word ÎłĎ ÎźÎ˝ĎĎĎÎľĎÎźÎżĎ (ÎłĎ ÎźÎ˝ĎĎ gymnos, "naked" and ĎĎÎĎΟι sperma, "seed"), meaning "naked seeds". The name is based on the unenclosed condition of their seeds (called ovules in their unfertilized state). The non-encased condition of their seeds stands in contrast to the seeds and ovules of flowering plants (angiosperms), which are enclosed within an ovary. Gymnosperm seeds develop either on the surface of scales or leaves, which are often modified to form cones, or solitary as in Yew, Torreya, Ginkgo.
The gymnosperms and angiosperms together compose the spermatophytes or seed plants. The gymnosperms are divided into six phyla. Organisms that belong to the Cycadophyta, Ginkgophyta, Gnetophyta, and Pinophyta (also known as Coniferophyta) phyla are still in existence while those in the Pteridospermales and Cordaitales phyla are now extinct.
By far the largest group of living gymnosperms are the conifers (pines, cypresses, and relatives), followed by cycads, gnetophytes (Gnetum, Ephedra and Welwitschia), and Ginkgo biloba (a single living species). Roots in some genera have fungal association with roots in the form of micorrhiza(Pinus), while in some others(Cycas) small specialised roots called coralloid roots are associated with nitrogen fixing cyanobacteria.
Gnetum is a genus of gymnosperms, the sole genus in the family Gnetaceae and order Gnetales. They are tropical evergreen trees, shrubs and lianas. Unlike other gymnosperms, they possess vessel elements in the xylem. Some species have been proposed to have been the first plants to be insect-pollinated as their fossils occur in association with extinct pollinating scorpion flies. Molecular phylogenies based on nuclear and plastid sequences from most of the species indicate hybridization among some of the Southeast Asian species. Fossil-calibrated molecular-clocks suggest that the Gnetum lineages now found in Africa, South America and Southeast Asia are the result of ancient long-distance dispersal across seawater
The slides has been edited. visit for new one on https://www.slideshare.net/alihaider408/stelar-system-stele-its-types-and-evolutionedited-182037813
Sorry for inconvenience.
Stele is defined as a central vascular cylinder, with or without pith and delimited the cortex by endodermis.
Van Tieghem and Douliot (1886) recognized only three types of steles.
1-Protostele
2-Siphonostele
3-Solenostele
Stelar Theory:
Major highlights of stellar theory are:
Stele is a real entity and present universally in all higher plants.
Cortex and stele are two fundamental parts of a shoot system
Stele and cortex are separated by endodermis
⢠Gymnosperms (Gymnos = naked, Sperma = seed) include the small group of plants with naked seeds.
⢠The Gymnosperms originated in the Devonian period of the Paleozoic Era and formed the supreme vegetation in the Mesozoic Era.
Gnetum: A Powerpoint Presentation on Gymnospemsshivduraigaran
Â
The Gymnosperms are a group of seed-producing plants (spermatophytes) that includes conifers (Pinophyta), cycads, Ginkgo, and gnetophytes. The term "gymnosperm" comes from the Greek composite word ÎłĎ ÎźÎ˝ĎĎĎÎľĎÎźÎżĎ (ÎłĎ ÎźÎ˝ĎĎ gymnos, "naked" and ĎĎÎĎΟι sperma, "seed"), meaning "naked seeds". The name is based on the unenclosed condition of their seeds (called ovules in their unfertilized state). The non-encased condition of their seeds stands in contrast to the seeds and ovules of flowering plants (angiosperms), which are enclosed within an ovary. Gymnosperm seeds develop either on the surface of scales or leaves, which are often modified to form cones, or solitary as in Yew, Torreya, Ginkgo.
The gymnosperms and angiosperms together compose the spermatophytes or seed plants. The gymnosperms are divided into six phyla. Organisms that belong to the Cycadophyta, Ginkgophyta, Gnetophyta, and Pinophyta (also known as Coniferophyta) phyla are still in existence while those in the Pteridospermales and Cordaitales phyla are now extinct.
By far the largest group of living gymnosperms are the conifers (pines, cypresses, and relatives), followed by cycads, gnetophytes (Gnetum, Ephedra and Welwitschia), and Ginkgo biloba (a single living species). Roots in some genera have fungal association with roots in the form of micorrhiza(Pinus), while in some others(Cycas) small specialised roots called coralloid roots are associated with nitrogen fixing cyanobacteria.
Gnetum is a genus of gymnosperms, the sole genus in the family Gnetaceae and order Gnetales. They are tropical evergreen trees, shrubs and lianas. Unlike other gymnosperms, they possess vessel elements in the xylem. Some species have been proposed to have been the first plants to be insect-pollinated as their fossils occur in association with extinct pollinating scorpion flies. Molecular phylogenies based on nuclear and plastid sequences from most of the species indicate hybridization among some of the Southeast Asian species. Fossil-calibrated molecular-clocks suggest that the Gnetum lineages now found in Africa, South America and Southeast Asia are the result of ancient long-distance dispersal across seawater
Pteridophyta or Pteridophytes are Vascular Plants (also known as "seedless plants") that reproduce and disperse via spores. They do not produce either seeds or flowers.
Additional info:
+ Division Equisetophyta (horsetails & scouring rushes)
+ Division Psilotophyta (whisk ferns)
(This is our report in Botany 2.)
Made by: Sharmine Ballesteros (BS Biology 2A2-1)
The "Telome theory" of Walter Zimmermann (1930, 1952) is the most accepted theory that is based on fossil record and synthesizes the major steps in the evolution of vascular plants.
It describes how the primitive type of vascular plants developed from Rhynia like plants.
Pteridophyta or Pteridophytes are Vascular Plants (also known as "seedless plants") that reproduce and disperse via spores. They do not produce either seeds or flowers.
Additional info:
+ Division Equisetophyta (horsetails & scouring rushes)
+ Division Psilotophyta (whisk ferns)
(This is our report in Botany 2.)
Made by: Sharmine Ballesteros (BS Biology 2A2-1)
The "Telome theory" of Walter Zimmermann (1930, 1952) is the most accepted theory that is based on fossil record and synthesizes the major steps in the evolution of vascular plants.
It describes how the primitive type of vascular plants developed from Rhynia like plants.
Stelar System, Stele, its types and evolution(edited)Haider Ali Malik
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Stele is defined as a central vascular cylinder, with or without pith and delimited the cortex by endodermis.
Van Tieghem and Douliot (1886) recognized only three types of steles.
1-Protostele
2-Siphonostele
3-Solenostele
Stelar Theory:
Major highlights of stellar theory are:
Stele is a real entity and present universally in all higher plants.
Cortex and stele are two fundamental parts of a shoot system
Stele and cortex are separated by endodermis.
This is a Life Cycle of Shpagnum, A good content for Masters Students. (But this content is not made by me...but i thought that this will help many students who are in search for content)
Thank you đ
Soral & Sporangial Characters in Pteridophytes.pdfANAKHA JACOB
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Sporangia are Spore bearing structure.
⢠May be eusporangiate or leptosporangiate.
⢠Homo- or Heterosporous.
⢠Terminal/ Lateral/ aggregated into specialized structures.
Tassel is regarded as primitive and acrostichoid condition as advanced.
The sporangia on expanded sporophyll are with or without the
indusium(protective covering).
⢠The sori lacking indusia are exindusiate or naked (Gleicheniaceae).
Equisetum popularly known a the âhorse-tailâ or âscouring rushâ.
It is now represented by nearly 30 species which are seen world wide except in Australia and New Zealand.
Some species prefer damp and shady places while others grow in marshes, ponds or stream banks
Some are found in xerophytic habitats
Match the stele-type with its description.ProtosteleSiphonostele.pdfdhavalbl38
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Match the stele-type with its description.
Protostele
Siphonostele
Eustele
Dispersed stele
The xylem forms an uninterrupted cylinder within a cylinder of phloem; found in the stems of
very simple seedless vascular plants.
A cylinder of phloem surrounds a cylinder of xylem which surrounds another cylinder of
phloem, with a pith of parenchyma cells at the center; found in the stems of ferns and fern allies.
The stele is broken into vascular bundles that are arranged in a ring with the phloem on the
outside and the xylem on the inside; commonly found in gymnosperms and dicots.
The stele is broken into vascular bundles that are scattered in cross section so that the orientation
of xylem and phloem is inconsistent from vascular bundle to vascular bundle; found in
monocots. - A. B. C. D.
Protostele - A. B. C. D.
Siphonostele - A. B. C. D.
Eustele - A. B. C. D.
Dispersed steleA.
The xylem forms an uninterrupted cylinder within a cylinder of phloem; found in the stems of
very simple seedless vascular plants.B.
A cylinder of phloem surrounds a cylinder of xylem which surrounds another cylinder of
phloem, with a pith of parenchyma cells at the center; found in the stems of ferns and fern
allies.C.
The stele is broken into vascular bundles that are arranged in a ring with the phloem on the
outside and the xylem on the inside; commonly found in gymnosperms and dicots.D.
The stele is broken into vascular bundles that are scattered in cross section so that the orientation
of xylem and phloem is inconsistent from vascular bundle to vascular bundle; found in
monocots.
Solution
A). The xylem forms an uninterrupted cylinder within a cylinder of phloem; found in the stems
of very simple seedless vascular plants. ---> Protostele
B). A cylinder of phloem surrounds a cylinder of xylem which surrounds another cylinder of
phloem, with a pith of parenchyma cells at the center; found in the stems of ferns and fern allies.
---> Siphonostele
C). The stele is broken into vascular bundles that are arranged in a ring with the phloem on the
outside and the xylem on the inside; commonly found in gymnosperms and dicots. ----> Eustele
D). The stele is broken into vascular bundles that are scattered in cross section so that the
orientation of xylem and phloem is inconsistent from vascular bundle to vascular bundle; found
in monocots ----> Dispersed stele.
This PPT explores the different type of plant tissue systems and their good coordination for the sake of structural and functional integrity along with other attributes.
Slide 1: Title Slide
Extrachromosomal Inheritance
Slide 2: Introduction to Extrachromosomal Inheritance
Definition: Extrachromosomal inheritance refers to the transmission of genetic material that is not found within the nucleus.
Key Components: Involves genes located in mitochondria, chloroplasts, and plasmids.
Slide 3: Mitochondrial Inheritance
Mitochondria: Organelles responsible for energy production.
Mitochondrial DNA (mtDNA): Circular DNA molecule found in mitochondria.
Inheritance Pattern: Maternally inherited, meaning it is passed from mothers to all their offspring.
Diseases: Examples include Leberâs hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Slide 4: Chloroplast Inheritance
Chloroplasts: Organelles responsible for photosynthesis in plants.
Chloroplast DNA (cpDNA): Circular DNA molecule found in chloroplasts.
Inheritance Pattern: Often maternally inherited in most plants, but can vary in some species.
Examples: Variegation in plants, where leaf color patterns are determined by chloroplast DNA.
Slide 5: Plasmid Inheritance
Plasmids: Small, circular DNA molecules found in bacteria and some eukaryotes.
Features: Can carry antibiotic resistance genes and can be transferred between cells through processes like conjugation.
Significance: Important in biotechnology for gene cloning and genetic engineering.
Slide 6: Mechanisms of Extrachromosomal Inheritance
Non-Mendelian Patterns: Do not follow Mendelâs laws of inheritance.
Cytoplasmic Segregation: During cell division, organelles like mitochondria and chloroplasts are randomly distributed to daughter cells.
Heteroplasmy: Presence of more than one type of organellar genome within a cell, leading to variation in expression.
Slide 7: Examples of Extrachromosomal Inheritance
Four Oâclock Plant (Mirabilis jalapa): Shows variegated leaves due to different cpDNA in leaf cells.
Petite Mutants in Yeast: Result from mutations in mitochondrial DNA affecting respiration.
Slide 8: Importance of Extrachromosomal Inheritance
Evolution: Provides insight into the evolution of eukaryotic cells.
Medicine: Understanding mitochondrial inheritance helps in diagnosing and treating mitochondrial diseases.
Agriculture: Chloroplast inheritance can be used in plant breeding and genetic modification.
Slide 9: Recent Research and Advances
Gene Editing: Techniques like CRISPR-Cas9 are being used to edit mitochondrial and chloroplast DNA.
Therapies: Development of mitochondrial replacement therapy (MRT) for preventing mitochondrial diseases.
Slide 10: Conclusion
Summary: Extrachromosomal inheritance involves the transmission of genetic material outside the nucleus and plays a crucial role in genetics, medicine, and biotechnology.
Future Directions: Continued research and technological advancements hold promise for new treatments and applications.
Slide 11: Questions and Discussion
Invite Audience: Open the floor for any questions or further discussion on the topic.
This pdf is about the Schizophrenia.
For more details visit on YouTube; @SELF-EXPLANATORY;
https://www.youtube.com/channel/UCAiarMZDNhe1A3Rnpr_WkzA/videos
Thanks...!
Observation of Ioâs Resurfacing via Plume Deposition Using Ground-based Adapt...SĂŠrgio Sacani
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Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Ioâs surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Ioâs trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Ioâs surface using adaptive
optics at visible wavelengths.
Cancer cell metabolism: special Reference to Lactate PathwayAADYARAJPANDEY1
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Normal Cell Metabolism:
Cellular respiration describes the series of steps that cells use to break down sugar and other  chemicals to get the energy we need to function.
Energy is stored in the bonds of glucose and when glucose is broken down, much of that energy is released. Â
Cell utilize energy in the form of ATP.
The first step of respiration is called glycolysis. In a series of steps, glycolysis breaks glucose into two smaller molecules -Â a chemical called pyruvate. A small amount of ATP is formed during this process.Â
Most healthy cells continue the breakdown in a second process, called the Kreb's cycle. The Kreb's cycle allows cells to âburnâ the pyruvates made in glycolysis to get more ATP.
The last step in the breakdown of glucose is called oxidative phosphorylation (Ox-Phos).
It takes place in specialized cell structures called mitochondria. This process produces a large amount of ATP.  Importantly, cells need oxygen to complete oxidative phosphorylation.
If a cell completes only glycolysis, only 2 molecules of ATP are made per glucose. However, if the cell completes the entire respiration process (glycolysis - Kreb's - oxidative phosphorylation), about 36 molecules of ATP are created, giving it much more energy to use.
IN CANCER CELL:
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.Â
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.Â
introduction to WARBERG PHENOMENA:
WARBURG EFFECT Usually, cancer cells are highly glycolytic (glucose addiction) and take up more glucose than do normal cells from outside.
Otto Heinrich Warburg (; 8 October 1883 â 1 August 1970) In 1931 was awarded the Nobel Prize in Physiology for his "discovery of the nature and mode of action of the respiratory enzyme.
WARNBURG EFFECT : Â cancer cells under aerobic (well-oxygenated) conditions to metabolize glucose to lactate (aerobic glycolysis) is known as the Warburg effect. Warburg made the observation that tumor slices consume glucose and secrete lactate at a higher rate than normal tissues.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
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Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.Â
 Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
The increased availability of biomedical data, particularly in the public domain, offers the opportunity to better understand human health and to develop effective therapeutics for a wide range of unmet medical needs. However, data scientists remain stymied by the fact that data remain hard to find and to productively reuse because data and their metadata i) are wholly inaccessible, ii) are in non-standard or incompatible representations, iii) do not conform to community standards, and iv) have unclear or highly restricted terms and conditions that preclude legitimate reuse. These limitations require a rethink on data can be made machine and AI-ready - the key motivation behind the FAIR Guiding Principles. Concurrently, while recent efforts have explored the use of deep learning to fuse disparate data into predictive models for a wide range of biomedical applications, these models often fail even when the correct answer is already known, and fail to explain individual predictions in terms that data scientists can appreciate. These limitations suggest that new methods to produce practical artificial intelligence are still needed.
In this talk, I will discuss our work in (1) building an integrative knowledge infrastructure to prepare FAIR and "AI-ready" data and services along with (2) neurosymbolic AI methods to improve the quality of predictions and to generate plausible explanations. Attention is given to standards, platforms, and methods to wrangle knowledge into simple, but effective semantic and latent representations, and to make these available into standards-compliant and discoverable interfaces that can be used in model building, validation, and explanation. Our work, and those of others in the field, creates a baseline for building trustworthy and easy to deploy AI models in biomedicine.
Bio
Dr. Michel Dumontier is the Distinguished Professor of Data Science at Maastricht University, founder and executive director of the Institute of Data Science, and co-founder of the FAIR (Findable, Accessible, Interoperable and Reusable) data principles. His research explores socio-technological approaches for responsible discovery science, which includes collaborative multi-modal knowledge graphs, privacy-preserving distributed data mining, and AI methods for drug discovery and personalized medicine. His work is supported through the Dutch National Research Agenda, the Netherlands Organisation for Scientific Research, Horizon Europe, the European Open Science Cloud, the US National Institutes of Health, and a Marie-Curie Innovative Training Network. He is the editor-in-chief for the journal Data Science and is internationally recognized for his contributions in bioinformatics, biomedical informatics, and semantic technologies including ontologies and linked data.
2. ⢠The stelar theory was proposed by, Van Tiegham
and Douliot in 1886. According to which the root
and stem are fundamentally similar in gross
anatomy, because in both the cortex encloses the
central part of the axis, called the stele. According
to them, stele is the core of the axis, which
includes the vascular system, interfascicular
portion, the pith (if present), and some
surrounding portion of the fundamental tissue in
the vicinity of vascular bundles (pericycle).
⢠The term stele is applied to the primary tissue
only. On the basis of structural variations, in the
primary vascular system, following types of steles
have been recognized.
3. 1. Protostele
⢠This is the simplest type of stele.
It consists of a solid central
column of vascular tissue. Pith is
absent. Xylem is located in the
centre surrounded by phloem. On
the basis of shape of xylem, the
following types of protosteles
have been recognized:
⢠a. Haplostele:
⢠It has a smooth core of xylem
surrounded by a uniform layer of
phloem, e.g. Rhynia, Cooksonia
and Selaginella kraussiana
4. ⢠b. Actinostele:
⢠It has a xylem core with
radiating ribs
(starshaped = stellate).
In actinostele, phloem
is present in the form
of separate patches
alternating with
projecting parts of
xylem, e.g. Lycopodium
serratum, Psilotum
nudum
5. ⢠c. Plectostele:
⢠In this type of
protostele, xylem occurs
in the form of separate
plates which lie parallel
to one another, with
phloem situated
between them. It is
found in Lycopodium
volubile, L. clavatum,
etc.
6. ⢠Mixed protostele with
phloem:
⢠In this stele xylem
groups are scattered
in the form of
irregular patches that
are embedded in the
ground mass of
phloem, e.g.,
Lycopodium cernuum
7. ⢠Mixed protostele with pith parenchyma:
⢠In this stele xylem groups are scattered in the
form of irregular patches that are embedded
in the ground mass of parenchyma,
⢠e.g. Hymenophyllum demissum
8. 2. Siphonostele or medullated
protostele
⢠A type of stele in which there is present a pith
in the central region, is called a siphonostel. In
siphonostele, vascular tissue is arranged in the
form of a hollow cylinder, with distant pith in
the centre. It is found in the stems of most
members of Filicophyta. It is of the following
two types:
9. ⢠a. Ectophloic siphonostele: It is a type of siphonostele
where xylem cylinder lies next to the pith and is
surrounded by the phloem cylinder on the outer side. It
is found in Osmunda, Equisetum, etc.
⢠b. Amphiphloic siphonostele: In this type of siphonostele
the pith is surrounded by inner endodermis, inner
pericycle, inner phloem, xylem, outer phloem, outer
pericycle and outer endodermis. So in this case phloem
surrounds the xylem internally as well as externally. It is
found in Adiantum, Marsilea, etc.
10. ⢠In both ectophloic and amphiphloic
siphonosteles, vascular tissue occurs as
continuous cylinder. This is because the leaf
traces do not break the vascular cylinder. Such
plants in which the vascular supply to the leaf
is without any break in vascular cylinder are
called microphyllous.
11. 3. Solenostele
⢠This is similar to siphonostele in having central pith, but differs in
producing leaf gaps, wherever leaf traces originate. Thus due to
production of leaf gaps, the cylinder becomes dissected at places.
⢠This type of solenostele may be ectophloic or amphiphloic,
depending upon the type of siphonostele from which it is produced.
Such plants where leaf gaps occur in vascular cylinder are called
magaphyllous
12. ⢠In many siphonostelic Filicophyta, leaves
are inserted on the stem in close
succession. In such cases, leaf gaps overlap
in their longitudinal extent to such a
degree that vascular cylinder of stem
appears dissected into tubular network of
interconnected longitudinal strands
(meristeles), separated from one another
by parenchymatous tissue (leaf gaps).
⢠These meristeles in a transverse section
appear arranged in a ring. Such a stele is
known as dissected siphonostele or
dictyostele. The vascular parts of a
dictyostele between two neighbouring leaf
gaps, appearing in transverse section as
separate strands, are termed as
meristeles. In a Dictyostele, each meristele
has the general structure of a protostele,
e.g. Dryopteris filix-max, Pteris vittata
4. Dictyostele
13. 5. Eustele
⢠This is a modification of
siphonostele, in which
vascular system consists of
a ring of collateral or
bicollateral vascular
bundles. These are
separated from one
another by a wide
medullary or interfasicular
regions and leaf gaps are
not clearly distinguishable.
⢠It is found in the stems of
gymnosperms and
angiosperms
14. 6. Atactostele
⢠This is the most
complex type of stele.
In this type, the
vascular bundles are
irregularly dispersed
in the ground tissue as
in the stems of
monocotyledons
15. ⢠Polycyclic stele: When more than one
steles are present in the axis of
pteridophytes, e.g. 2 in Selaginella
kraussiana, 16 in S. laevigata, the
condition is called polycyclic stele.
16. Stelar evolution
⢠According to Jeffrey (1898), protostele is the
most primitive type of stele, from a phylogenetic
stand point, from which other types of steles
have evolved in the course of evolutionary
specialization.
⢠It is considered to be the fundamental stelar
organisation that was present in the earliest
vascular plants, and is now retained by some
living vascular cryptogams such as Psilotum,
Tmesipteris and Lycopodium, etc.
⢠the extinct Psilophytales also possessed
protostelic vascular organisation.
17. ⢠In its simplest form, protostele is haplostelic.
During further elaboration, the central core of
xylem became irregular and assumed almost a
star-like shape. Such a modification of stele is
termed as actinostele. As a result of further
evolution, the xylem splits up into a number of
parallel plates alternating with phloem. Such a
modification is called plectostele. It is found in
some species of Lycopodium.
⢠Haplostele to actinostele, and then to
plectostele, is considered to be one line of
evolution of the protostele.
⢠It is regarded as Lycopsid line of evolution.
18. ⢠The various types of protosteles may show
relative variation in the position of protoxylem
and metaxylem. It may be exarch with the
protoxylem near the periphery of the xylem
strands, or may be endarch with the
protoxylem at the inner surface. In the
mesarch condition, metaxylem is present both
towards the outer and inner sides of
protoxylem.
⢠The endarch condition is considered to be the
most evolved and exarch condition as the
primitive in the context of stelar evolution.
19. ⢠Another very important evolutionary change that
occurred in the protostele was the appearance of the
central pith, which in turn led to the development of
more complicated stelar types. Two theories have been
proposed accounting the phylogenetic origin of the
pith. These are: I) Intrastelar theory, II) Extrastelar
theory
⢠I). Intrastelar theory: According to intrastelar origin of
pith or expansion theory, the inner vascular tissue
metamorphosed into the parenchymatous pith. The
occurrence of mixed pith in some living forms supports
this view. A mixed pith shows tracheids within the
parenchymatous pith. This may be looked upon as a
transition stage between a true protostele and true
siphonostele.
20. ⢠II) Extrastelar theory: According to the
extrastelar origin of pith or invasion theory
the pith is cortical in origin. The
parenchymatous cortex is said to have
intruded through the leaf gaps and branch
gaps into the centre of vascular cylinder to
give rise to the pith. But this cortical invasion
could not have produced polycyclic
siphonostele.
⢠Eames (1936) considered that in primitive
forms, it may be intrastelar in origin, and in
higher forms extrastelar in origin.
21. ⢠Appearance of pith led to the conversion of the
protostele into a new type of stele, called the
siphonostele. Elaboration of siphonostele also
followed two courses of evolution, as follows:
⢠i). The appearance of pith resulted in the formation
of a stele consisting of a central pith surrounded by a
complete ring of xylem, which in turn was
surrounded by a complete ring of outer phloem,
pericycle and endodermis. Such a stele was named
as ectophloic siphonostele.
⢠In its simplest form such a stele is uninterrupted by
leaf gaps and is called cladosiphonic. In the
magaphyllous vascular plants, the ectopholic
siphonostele became interrupted by the appearance
of leaf gaps, which is now called phyllosiphonic.
22. ⢠In case the leaf gaps do not overlap, the stele is,
interrupted only at considerable distances
(nodes) by one leaf gap, so in between the two
leaf gaps, the vascular cylinder remains complete.
Such a stele is also called solenostele or
siphoneustele.
⢠During the course of evolution, leaf gaps on the
stem overlap and lead to formation of a much
dissected stelar organisation, called eustele. It is
made up of a number of separate and collateral
vascular bundles.
⢠In certain cases, the vascular bundles are
scattered, as in monocotyledons, this kind of
stele is termed as atactostele.
23. ⢠ii). During another line of evolution, the
medullation of protostele was followed by the
appearance of phloem on either side of the
xylem; likewise internal pericycle and endodermis
also appeared. Such a stele led to the formation
of amphiphloic siphonostele. It may be
cladosiphonic or phyllosiphonic.
⢠The phyllosiphonic amphiphloic siphonostele
with only one leaf gap at the node is called
amphiphloic solenostele.
⢠In case the leaf gaps overlap, the resultant stele is
called the dictyostele.
24. ⢠In many eusporangiate and leptosporangiate
ferns, the dictyostelic stems are protostelic at
their bases.
⢠Recent experimental studies also reveal that
dictyostelic condition can be changed to
solenostelic, or even to protostelic condition by
removing the young leaf primordial from shoot
apices.
⢠All these observations prove that protostele is the
basic or the fundamental stelar type, from which
the complicated steles or vascular systems arose
by elaboration.
25. ⢠Among the pteridophytes, polycyclic stele is the
most advanced condition exhibited by some ferns
like Marattia, Matonia, etc. It also originated
from the protostelic condition by further
elaboration that in Matonia pectinata, there is a
regular transition from protostelic condition to
solenostele and then to polycyclic condition. This
developmental phenomenon is termed as
recapitulation.
⢠Occurrence of such a developmental
phenomenon leads further support to Jeffrey's
view that protostele is the primitive condition.
27. ⢠Thus, the evolution of stellar organisation has
taken place along several independent lines;
even a single genus, like Gleichenia, shows
some species with protostelic structure, and
some with the siphonostelic organisation.
⢠So the stellar structure has not been of much
significance in establishing phylogenetic
relationships.