Taxus baccata commonly known as ‘Yew’, is an evergreen tree attaining a height of 9-20 metres with a massive trunk. Taxus is usually dioecious, but occasionally monoecious trees are also reported.
The reproductive structures become prominent on the plant in February-March. The male and female plants do not show any distinction in their vegetative organization. The differentiation between them can be made only when the plants are in the flowering or fruiting stage. Vegetative reproduction in Taxus is not known.
Taxus -Morphological ,anatomical and reproductive features &Economic importanceJasmine Mariya
Taxus is a representative of conifers which is a prominent member in that group.It shows so many remarkable features in its morphology , Anatomy ,Reproduction and life cycle. It's economically importance is also great. This presentation is a overall description about Taxus.
This PPT contains the application of Plant Anatomy in the field of Pharmacognosy & Plant systemics with number of examples to explore the beauty of this subject .
Taxus -Morphological ,anatomical and reproductive features &Economic importanceJasmine Mariya
Taxus is a representative of conifers which is a prominent member in that group.It shows so many remarkable features in its morphology , Anatomy ,Reproduction and life cycle. It's economically importance is also great. This presentation is a overall description about Taxus.
This PPT contains the application of Plant Anatomy in the field of Pharmacognosy & Plant systemics with number of examples to explore the beauty of this subject .
Ginkgo is known as a Living Fossil.Anatomy of Ginkgo clearly shows primary and secondary structures. sex in Ginkgo is determined by sex chromosomes (XY in male and XX in female). Reproductive bodies of Ginkgo are most primitive among living seed plants except some Cycadales. Ginkgos are dioecious, with separate sexes, some trees being female and others being male. Male plants produce small pollen cones with sporophylls, each bearing two microsporangia spirally arranged around a central axis. Female plants do not produce cones. Two ovules are formed at the end of a stalk, and after pollination, one or both develop into seeds. The fertilization of ginkgo seeds occurs via motile sperm, as in cycads, ferns, mosses and algae.
A laticifer is a type of elongated secretory cell found in the leaves and/or stems of plants that produce latex and rubber as secondary metabolites.
Thin walled
Greately elongated
Much branched structure
Which contain milky juice
Complex composition called latex
These are following two types:-
Articulated laticifers
Non-articulated laticifers
It is called as “living fossil”
The whole order is extincted except one species Ginkgo biloba
This order was occurred in Triassic periods of Mesozoic age (200,000,000 years ago)
This order consists of 16 genera and many species (all in fossil forms except one)
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
Ginkgo is known as a Living Fossil.Anatomy of Ginkgo clearly shows primary and secondary structures. sex in Ginkgo is determined by sex chromosomes (XY in male and XX in female). Reproductive bodies of Ginkgo are most primitive among living seed plants except some Cycadales. Ginkgos are dioecious, with separate sexes, some trees being female and others being male. Male plants produce small pollen cones with sporophylls, each bearing two microsporangia spirally arranged around a central axis. Female plants do not produce cones. Two ovules are formed at the end of a stalk, and after pollination, one or both develop into seeds. The fertilization of ginkgo seeds occurs via motile sperm, as in cycads, ferns, mosses and algae.
A laticifer is a type of elongated secretory cell found in the leaves and/or stems of plants that produce latex and rubber as secondary metabolites.
Thin walled
Greately elongated
Much branched structure
Which contain milky juice
Complex composition called latex
These are following two types:-
Articulated laticifers
Non-articulated laticifers
It is called as “living fossil”
The whole order is extincted except one species Ginkgo biloba
This order was occurred in Triassic periods of Mesozoic age (200,000,000 years ago)
This order consists of 16 genera and many species (all in fossil forms except one)
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
Class 12||Chapter 2|| Sexual Reproduction in flowering plantsPrathamBiology
This chapter includes flowers, their detailed structure and developmental processess which took place durin sexual reproduction. Helpful for Board and NEET students.
Fell free for any query or suggestion
Mail us on: biologypratham@gmail.com
Website : www.prathambiology.in
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 😊
Kingdom Plantae presented by Vrushali Gharat to Mr. Kailash vilegaveKailash Vilegave
Classification Of Kingdom Plantae, Classification Of Kingdom Plantae, Economic importance Algae.
Ulothrix
Reproduction
Mosses and Liverwort
life cycle of all plants.
Gymnosperms definition
Morphological characters of Gymnosperms
Anatomy of Gymnosperms
Cycas
General character of cycas
Sexual reproduction in cycas
Asexual reproduction in cycas
Economical importance of cycas
Pinus
Characters of pinus
Sexual reproduction in pinus
Asexual reproduction in pinus
Importance of pinus
Roots anatomy
Stem anatomy
Xylem
Phloem
Equisetum popularly known a the ‘horse-tail’ or ‘scouring rush’.
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
Holding company first came into existence in the US. It was created to overcome the restrictions imposed by the Anti-trust legislation. They were formed because businessmen wanted to have concerns under common control and within the framework of law.
Under the companies Act, 1956, a holding company is any company which holds more than half of the equity share capital of other companies or controls the composition of the board of directors of other companies. Type of business organization that allows a firm (called parent) and its directors to control or influence other firms (called subsidiaries). This arrangement makes venturing outside one's core industry possible and, under certain conditions, to benefit from tax consolidation, sharing of operating losses, and ease of divestiture. The legal definition of a holding company varies with the legal system. Some require holding of a majority (80 percent) or the entire (100 percent) voting shares of the subsidiary whereas other require as little as five percent.
Account which is prepared in the books of head office related to branch to ascertion branch profit or loss are called branch Account and to record. The Transacetions in the bppk of head office related to branch account is called Branch Accounting.
To help in controlling branch activites.
2. To ascertain the profit or loss each branch separately.
3. To ascertain the financial position of each branch at the end of the accounting period.
4.To arress the progress and performance of each branch.
5. To ascertain the requirement of stock and each for each branch.
6. To ascertain whether the branch should be expanded or closed
The exact knowledge about the interior on the earth still remains an enigma.
Knowledge of the structure, composition, and the process going on within it would currently help scientists answer questions regarding crustal motion, earth quakes, the volcanic eruptions and the origins of the continents and of the earth itself. As the earth gradually solidified, heavier elements slowly sank towards the centre and lighter elements slowly moved upwards to the surface concentrating in the earth’s crust.
Earth’s interior is arranged roughly in concentric layers, each one distinct either in chemical composition or temperature with heat radiating outward from the centre by conduction and then by physical convection in the more plastic levels nearer the surface.
Magnetic properties of matter are their macroscopic behaviour in a magnetic field under varying conditions ; These are : permeability ,susceptibility, hysteresis retentivity and coercivity. Permeability : Suppose that a long unmagnetised bar of a substance is placed in a uniform magnetic field of induction B0. Before the specimen is introduced into the field it is represented by a set of parallel lines known as lines of inducton.
Map projection is a systematic drawing of parallel of latitudes and meridians of longitude on a plane surface for the whole earth or a part of it on a certain scale so that any point on the earth surface may correspond to that on the drawing.
Maps cannot be created without map projections. All map projections necessarily distort the surface in some fashion.
Depending on the purpose of the map, some distortions are acceptable and others are not; therefore, different map projections exist in order to preserve some properties of the sphere-like body at the expense of other properties.
There is no limit to the number of possible map projections.
Projectile is any object thrown into the space upon which the only acting force is gravity. The motion of a projectile is said to be projectile motion. When we throw a ball into the air (not vertically upwards), it describes a curved path. This curved path is called trajectory.
The golden rules in accounting or rules of debit and creditkaslinsas
Journal Entries cannot be recorded without some rules. The rules which are used to record a journal entry are called Golden rules of Accounting. It means debit the person who receives something from the business
Valuation means an estimation of the worth of something which is carried out by a professional valuer.
In context of finance items that are usually valued are financial asset (marketable securities, patent , goodwill) or liability (bond issued by company)
Bacteria are the simplest, the smallest, and the most successful microorganisms.
They were first discovered by Anton Leeuwenhoek (1676).
In the five kingdom classification, they are placed in Kingdom Monera. Reproduction: Vegetative Reproduction, Sexual Reproduction & Asexual Reproduction.
The genus Coleochaete is represented by about 10 species, out of which 3 species are found in India. They grow in fresh water either as epiphytes on different angiosperms. They show much variation in their heterotrichous nature. Due to well-developed prostrate system, it forms discoid thailus and looks like
pseudo- parenchyma of one cell in thickness.
Archaebacteria are the oldest organisms living on the Earth. They are
unicellular prokaryotes and belong to the kingdom, Archaea. They were first
discovered in 1977 and classified as bacteria. Most archaebacteria appear like
bacteria, when observed under the microscope. However, they are quite
different from bacteria and eukaryotic organisms.
Archaebacteria are found in very harsh conditions such as in the volcanic vents
or at the bottom of the sea. They can easily survive in such extreme
environment as sea vents releasing sulfide-rich gases, hot springs, or boiling
mud around volcanoes.
A mutation is a change that occurs in our DNA sequence, either due to mistakes when DNA is copied or as the result of environmental factors such as UV light. The DNA sequence of a gene can be altered in a number of ways. Gene mutations have varying effects on health, depending on where they occur and whether they alter the function of essential proteins. Mutations are two types that are Gene mutation and Chromosome mutation. Gene mutation are further divided into Point and frameshift mutation. Point mutation are three types ie. Silent mutation, Missense mutation and Nonsense mutation. Frameshift mutation are of two types that are addition and deletion. Chromosome mutations are further classified into Deletion, duplication, inversion and translocation.
Potato is a herbaceous perennial plant in the family Solanaceae which is grown for its edible tubers. the leaves can reach 10–30 cm (4–12 in) in length and 5–15 cm (2–6 in) wide. The potato plant produces white or blue flowers and yellow-green berries. It is grown as annual plants, surviving only one growing season. It grows best in cooler climates. Potatoes require a deep, fertile, loose, well-draining soil with a pH between 5.8 and 6.5 and will grow optimally at daytime temperatures between 18 and 27°C (65–80°F) and night time temperatures between 12 and 18°C (55–65°F). Potatoes are usually grown from seed potatoes. Each piece of planting material should have at least two eyes. Seed potatoes and pieces can be planted 0–2 weeks after the last frost. All tubers should be harvested when the vines have died. Harvest the tubers by gently digging them up with a fork. Do not wash the tubers prior to storing. Potatoes can also be processed into starch, alcohol or flour.
Chlamydomonas is unicellular, motile green algae. In this presentation the systematic position, occurrence, structure and different types of reproduction is being explained. palmella stage in vegetative reproduction is one of the outstanding character found among the other algae.
Francesca Gottschalk - How can education support child empowerment.pptxEduSkills OECD
Francesca Gottschalk from the OECD’s Centre for Educational Research and Innovation presents at the Ask an Expert Webinar: How can education support child empowerment?
Executive Directors Chat Leveraging AI for Diversity, Equity, and InclusionTechSoup
Let’s explore the intersection of technology and equity in the final session of our DEI series. Discover how AI tools, like ChatGPT, can be used to support and enhance your nonprofit's DEI initiatives. Participants will gain insights into practical AI applications and get tips for leveraging technology to advance their DEI goals.
Macroeconomics- Movie Location
This will be used as part of your Personal Professional Portfolio once graded.
Objective:
Prepare a presentation or a paper using research, basic comparative analysis, data organization and application of economic information. You will make an informed assessment of an economic climate outside of the United States to accomplish an entertainment industry objective.
A Strategic Approach: GenAI in EducationPeter Windle
Artificial Intelligence (AI) technologies such as Generative AI, Image Generators and Large Language Models have had a dramatic impact on teaching, learning and assessment over the past 18 months. The most immediate threat AI posed was to Academic Integrity with Higher Education Institutes (HEIs) focusing their efforts on combating the use of GenAI in assessment. Guidelines were developed for staff and students, policies put in place too. Innovative educators have forged paths in the use of Generative AI for teaching, learning and assessments leading to pockets of transformation springing up across HEIs, often with little or no top-down guidance, support or direction.
This Gasta posits a strategic approach to integrating AI into HEIs to prepare staff, students and the curriculum for an evolving world and workplace. We will highlight the advantages of working with these technologies beyond the realm of teaching, learning and assessment by considering prompt engineering skills, industry impact, curriculum changes, and the need for staff upskilling. In contrast, not engaging strategically with Generative AI poses risks, including falling behind peers, missed opportunities and failing to ensure our graduates remain employable. The rapid evolution of AI technologies necessitates a proactive and strategic approach if we are to remain relevant.
Safalta Digital marketing institute in Noida, provide complete applications that encompass a huge range of virtual advertising and marketing additives, which includes search engine optimization, virtual communication advertising, pay-per-click on marketing, content material advertising, internet analytics, and greater. These university courses are designed for students who possess a comprehensive understanding of virtual marketing strategies and attributes.Safalta Digital Marketing Institute in Noida is a first choice for young individuals or students who are looking to start their careers in the field of digital advertising. The institute gives specialized courses designed and certification.
for beginners, providing thorough training in areas such as SEO, digital communication marketing, and PPC training in Noida. After finishing the program, students receive the certifications recognised by top different universitie, setting a strong foundation for a successful career in digital marketing.
June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
A review of the growth of the Israel Genealogy Research Association Database Collection for the last 12 months. Our collection is now passed the 3 million mark and still growing. See which archives have contributed the most. See the different types of records we have, and which years have had records added. You can also see what we have for the future.
"Protectable subject matters, Protection in biotechnology, Protection of othe...
Taxus
1. St. Xavier’s College, Mahuadanr
Department of Botany Asst. Prof. Sr. Kaslin Juliat
Taxus
Morphological Features
1. Taxus baccata (Fig. 12.1), commonly
known as ‘Yew’, is an evergreen tree
attaining a height of 9-20 metres with a
massive trunk.
2. The stem is profusely branched and
remains covered with a thin brown-
coloured bark.
3. It differs from Pinus in not possessing
dimorphic branches.
4. All the branches are of unlimited growth
and form a very dense canopy, thus
making Taxus a shade-providing tree.
5. Only the green leaves are present on the
vegetative branches.
6. The leaves are linear, small, only 2-3 cm.
long and spirally arranged
7. Each leaf possesses a single strong vein
and recurved margins.
8. The upper surface is dark green while the
lower surface is pale or rusty red in
colour.
9. The apex is sharply pointed mainly because of accumulation of silica.
10.This sharply pointed apex may cause death of catties eating these leaves.
11.Each leaf is shortly stalked. The stalk broadens into a flat persistent base which
shows a slight twist.
12.The scaly leaves present on the fertile shoot are opposite and decussate.
13.Taxus possesses a long and well- developed tap-root.
14.The roots are deep-feeders and highly branched.
Internal Structures of Taxus
(i) Stem
1. In transverse section the stem is
irregular in outline and resembles
Pinus in structure.
2. It is surrounded by a thickly
cuticularised single-layered epidermis.
3. Inner to the epidermis is
parenchymatous cortex having some
tannin-filled cells.
2. St. Xavier’s College, Mahuadanr
Department of Botany Asst. Prof. Sr. Kaslin Juliat
4. It is followed by endodermis and
sclerenchymatous pericycle.
5. The young stem shows a ring of
conjoint, collateral, open and
endarch vascular bundles
enclosing a distinct pith in the
centre.
6. The protoxylem consists of spiral
tracheids, and the phloem
contains sieve cells with sieve
plates and phloem parenchyma.
7. Companion cells are absent.
8. The cambium is persistent and
develops a thick vascular
cylinder due to secondary
growth.
9. The cambium cuts secondary
phloem towards outer side and
secondary xylem towards inner side .
10.The secondary wood is devoid of resin
canals and wood parenchyma.
11.Its tracheids show uniseriate bordered
pits only on their radial walls.
12.The tracheids also show spiral
thickenings.
13.The medullary rays are uniseriate and
homogeneous but in Taxus baccata
they are sometimes bi-senate
14.The wood is strong and dense.
15.Due to the presence of tertiary spirals the wood is elastic in nature.
16.Phellogen may develop in the older stems showing extrastelar secondary’
growth.
(ii) Root
Except that of the absence of resin canals, the root anatomy of Taxus resembles very
much with that of Pinus. The root is diarch.
(iii) Leaf
1. The leaf is dorsiventral.
2. It shows xerophytic characters.
3. Upper and lower epidermal cells are rectangular in shape and thickly
circularized.
4. The cuticle is comparatively thin on the lower surface.
5. The stomata are of sunken type and restricted only to the lower epidermis.
3. St. Xavier’s College, Mahuadanr
Department of Botany Asst. Prof. Sr. Kaslin Juliat
6. They are haplocheilic in development.
7. The mesophyll is differentiated into palisade and spongy-parenchyma.
8. The palisade is generally two-layered.
9. Only one vascular bundle is present in the mid-rib region.
10.Enclosed by a distinct endodermal layer or bundle sheath the collateral vascular
bundle contains phloem towards the lower side and xylem towards the upper
side.
11.Transfusion tissue is present on both the sides of the vascular bundle.
12.Resin canals are generally absent.
13.The xerophytic characters of the leaf include the presence of thick cuticle,
sunken stomata, transfusion tissue and differentiation of mesophyll into
palisade and spongy parenchyma.
Reproduction
1. Taxus is usually dioecious, but occasionally monoecious trees are also
reported.
2. The reproductive structures become prominent on the plant in February-March.
3. The male and female plants do not show any distinction in their vegetative
organization.
4. The differentiation between them can be made only when the plants are in the
flowering or fruiting stage. Vegetative reproduction in Taxus is not known.
(i) Male Strobilus or Male Flower
The ‘male flowers’ or ‘male strobili’ are usually
yellowish in colour and develop in the axil of foliage
leaves
Each strobilus contains a number of overlapping
sterile bracts Some of the bracts towards the tip of the
4. St. Xavier’s College, Mahuadanr
Department of Botany Asst. Prof. Sr. Kaslin Juliat
strobilus are replaced by stamens or
micro-sporangiophores.
Each stamen is shortly-stalked any has a
peltate disc bearing 4-8 pendant
microsporangia.
The microsporangia surround the stalk
completely.
The axis of the male strobilus contains a
broad apex which is consumed in the
formation of a stamen.
The microsporangia in the young male
strobilus are compactly arranged but at
maturity they get loosened and undergo
dehiscence.
The presence of peltate micro-
sporangiophores is one of the most
remarkable features of Taxus.
A mature microsporangium remains surrounded by an epidermal layer
followed by two wall layers and sporogenous tissue.
The outermost sporogenous cells differentiate into a tapetum.
10 The sporogenous cells start to behave as microspore mother cells which
undergo meiosis and form microspores or pollen grains.
The microspores remain arranged isobilaterally or tetrahedrally for quite
sometime.
The development of microsporangium is of eusporangiate type and is identical
with that of Pinus.
1. Four to eight archesporial cells develop hypo-dermally.
2. They divide and form wall layers and sporogenous tissue.
5. St. Xavier’s College, Mahuadanr
Department of Botany Asst. Prof. Sr. Kaslin Juliat
3. In Taxus canadensis the microsporangium develops from one or rarely two
hypodermal archesporial cells.
4. Each microspore remains surrounded by two layers, i.e. intine and exine.
5. It is uniaperturate, spheroidal and contains a mass of cytoplasm and a centrally
located nucleus.
(ii) Female Strobilus or Female Flower
1. The female strobili in Taxus are so highly reduced that
they hardly appear as cones or strobili.
2. They arise in the axils of leaves early in the season and
mature in the next season.
3. Each female reproductive organ consists of a short primary
axis having scaly leaves or bracts arranged in opposite
decussate manner.
4. A short secondary axis develops from the axil of upper
three scaly leaves.
5. This secondary axis bears a few pairs of scaly leaves and a
terminal ovule .
6. According to Dupler (1920) the primary axis functions
only as a vegetative branch of limited growth bearing the reproductive
secondary axis.
Ovule
1. The ovule is somewhat rounded or oval in shape and orthotropous.
2. A single thick integument is present.
3. Integument is free from the nucellus right up to its base forming a long
micropyle.
4. The integument is differentiated into outer fleshy, middle stony and inner
fleshy layers.
5. Two vascular strands enter the integument from the base of the ovule and reach
up to its top.
6. St. Xavier’s College, Mahuadanr
Department of Botany Asst. Prof. Sr. Kaslin Juliat
6. A ring-like outgrowth develops from the base of the integument.
7. It surrounds the entire ovule.
8. It is called ‘aril’ or ‘cupule’
9. Aril is green and saucer-shaped when young but at maturity it is red and cup-
shaped.
10.The aril also receives two vascular bundles but they are very minute and
rudimentary.
11.Pollen chamber and nucellar beak are absent in Taxus.
12.The apex of the female gametophyte changes into a flask-shaped structure
called tent-pole.
13.The tent-pole disappears in the later stages.
Generally, up to 10 archegonia develop
in the female gametophyte but
sometimes as many as 25 archegonia
may appear.
In the young ovule an archesporial
initial develops hypo-dermaly in the
nucellus.
It divides penclinally forming an outer
parietal cell and an inner primary
sporogenous cell
The latter divides again to form many
sporogenous cells, of which generally
one or more start to behave as
megaspore mother cells.
The megaspore mother cell divides
meiotically to form four megaspores
7. St. Xavier’s College, Mahuadanr
Department of Botany Asst. Prof. Sr. Kaslin Juliat
which remain arranged in a linear tetrad.
Generally, the lowermost megaspore remains functional and the remaining
three degenerate
The functional megaspore nucleus divides, re-divides and develops ultimately
into a multicellular gametophyte.
Gametophytes in Taxus
(i) Male Gametophyte
A microspore develops into a male
gametophyte.
It is uninucleate at the time of shedding.
Dispersal of the microspores takes
place by wind.
A few microspores are taken up to the
micropyle by the wind, where they are
caught into the pollination drop.
Through this drop the microspores are
taken up to nucellus where they
germinate.
At the time of germination, the
microspore nucleus divides and forms a
tube cell and a generative cell.
The exine ruptures and the intine comes
out to form a pollen tube.
The tube nucleus moves towards the tip of the pollen tube.
The generative cell divides soon into a stalk cell and a body cell .
In the later stages two unequal male gametes are formed by the division of the
body cell
The prothallial cells are absent in Taxus.
(ii) Female Gametophyte
1. The functional megaspore develops into the
female gametophyte.
2. It enlarges in size and its nucleus divides by
many free-nuclear divisions to form as many as
256 nuclei.
3. In Taxus baccata only 128 free-nuclei are
formed according to Favre-Duchartre (1958).
4. A central vacuole develops and thus the free
nuclei become panetal in position.
8. St. Xavier’s College, Mahuadanr
Department of Botany Asst. Prof. Sr. Kaslin Juliat
5. There is a centnpetal wall formation as in Pinaceae and ultimately the whole of
the tissue becomes cellular.
6. Certain archegonial initials are differentiated towards the micropylar end of the
cellular female gametophyte.
7. As already mentioned, as many as 25 archegonia develop in some cases.
8. The development of archegonium in Taxus is similar with that of Pinus.
9. Each archegonium contains 2 to 4 neck cells and a large venter containing an
egg nucleus
10.There is no venter canal cell.
11.The cytoplasm of the egg cell contains both small and large cytoplasmic
inclusions and a zone of mitochondria and lipid globules near the nucleus.
(iii) Fertilization:
1. The tip of the pollen tube present near the neck
of the archegonium, bursts, and both the male
gametes, along with stalk nucleus and tube
nucleus, are liberated into the archegonial venter
.
2. The functional male nucleus (larger one) and the
egg nucleus fuse and result in the formation of a
zygote.
3. The other three nuclei (i.e. stalk nucleus, tube nucleus and smaller male cell)
degenerate.
4. As there are several archegonia in the female gametophyte, several eggs may
be fertilized, resulting into a simple polyembryony.
5. But ultimately only a single embryo attains maturity.
Embryogeny in Taxus
1. The zygotic nucleus divides to form 16 to 32
nuclei.
2. Cell formation starts and soon the complete
structure becomes cellular.
3. A few cells at the tip of this pro-embryo
develop into the embryo while the cells
above it elongate and form suspensor.
4. The embryo gradually absorbs all the
endosperm on development, and the seed
thus becomes non-endospermic.
5. The fully mature embryo is orthotropous and
dicotyledonous.
6. Only one embryo matures in one ovule.
Seed of Taxus
1. Taxus seeds are covered by a three-layered seed
coat.
9. St. Xavier’s College, Mahuadanr
Department of Botany Asst. Prof. Sr. Kaslin Juliat
2. The outermost layer is thin, brown and detaches soon.
3. The middle layer is hard and stony while the innermost layer is fleshy.
4. The mature seeds are covered by a red coloured aril.
5. The aril serves to attract birds and help in dissemination.
Germination of Seed
1. The germination of seed is hypogeal.
2. The seed germinates into a seedling possessing two
cotyledonary leaves.
3. The foliage leaves arise in the coming year.
4. The cotyledonary leaves are larger than the normal
foliage leaves.
Economic Importance of Taxus
Besides its cultivation as an ornamental plant, the timber of Taxus baccata and
some other species is oily and heaviest of the soft woods. It is quite durable and
used for making decorative veneers, turnery, flowers and posts. Several other
types of decorative pieces are also made from its wood.
Due to the presence of a toxic alkaloid (taxine) in the leaves, shoots and seeds,
the entire plant of Taxus baccata is considered poisonous and also used in some
countries as a fish poison.
Its leaves also contain traces of ephedrine, and, therefore, used in bronchitis,
asthama and epilepsy. Seeds of T. baccata are used as sedative.