This is a detailed presentation on Morphology, anatomy and reproduction of Marchantia spp. with high quality pics and eye capturing transitions and animations
Gnetum: A Powerpoint Presentation on Gymnospemsshivduraigaran
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 γυμνόσπερμος (γυμνός gymnos, "naked" and σπέρμα 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 "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.
This is a detailed presentation on Morphology, anatomy and reproduction of Marchantia spp. with high quality pics and eye capturing transitions and animations
Gnetum: A Powerpoint Presentation on Gymnospemsshivduraigaran
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 γυμνόσπερμος (γυμνός gymnos, "naked" and σπέρμα 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 "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.
• 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.
* The Gymnosperms originated in the Devonian period of the Palaeozoic Era and formed the supreme vegetation in the Mesozoic Era.
* It was Robert Brown (1827) who first recognised gymnosperms as a separate entity among plant kingdom.
• 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.
* The Gymnosperms originated in the Devonian period of the Palaeozoic Era and formed the supreme vegetation in the Mesozoic Era.
* It was Robert Brown (1827) who first recognised gymnosperms as a separate entity among plant kingdom.
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
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
Introduction to Sexual Reproduction in Flowering Plants, Flower, Structure of Flower, Male Reproductive Part of Flower (Stamens), Development of Anther walls, Anther Walls, Microsporangium (Pollen Sac)
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.
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Antifertility, Toxicity studies as per OECD guidelines
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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
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The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
Under Augustus, the empire experienced the Pax Romana, a 200-year period of relative peace and stability. Augustus reformed the military, established efficient administrative systems, and initiated grand construction projects. The empire's borders expanded, encompassing territories from Britain to Egypt and from Spain to the Euphrates. Roman legions, renowned for their discipline and engineering prowess, secured and maintained these vast territories, building roads, fortifications, and cities that facilitated control and integration.
The Roman Empire’s society was hierarchical, with a rigid class system. At the top were the patricians, wealthy elites who held significant political power. Below them were the plebeians, free citizens with limited political influence, and the vast numbers of slaves who formed the backbone of the economy. The family unit was central, governed by the paterfamilias, the male head who held absolute authority.
Culturally, the Romans were eclectic, absorbing and adapting elements from the civilizations they encountered, particularly the Greeks. Roman art, literature, and philosophy reflected this synthesis, creating a rich cultural tapestry. Latin, the Roman language, became the lingua franca of the Western world, influencing numerous modern languages.
Roman architecture and engineering achievements were monumental. They perfected the arch, vault, and dome, constructing enduring structures like the Colosseum, Pantheon, and aqueducts. These engineering marvels not only showcased Roman ingenuity but also served practical purposes, from public entertainment to water supply.
2. Gnetum is a genus of gymnosperms, the sole genus in the family Gnetaceae
and order Gnetales. They are tropical evergreen threes, shrubs and lianas.
Unlike other gymnosperms they possess vessel element in the xylem.
Systematic position:
Kingdom: Plantae
Division: Gnetophyta
Class: Gnetopsida
Order: Gnetales
Family: Gnetaceae
Genus: Gnetum
Distribution: The genus Gnetum includes about 35 species. The species are
distributed mainly in tropical and humid region of Africa, Asia and south
America. The five species of Gnetum have been reported in India.
3. Distribution of five Indian species:
1) Gnetum gnemon: A small tree or shrub with small drooping branches. The
species is found in Arunachal Pradesh, Assam, Manipur and Khasi and Jaintia
hiils.
2) Gnetum latifolium: An evergreen shrubs or climber. The species is mainly
distributed in Andaman and Nicobar Island.
3) Gnetum montanum: It is a large woody climbers. The species is confined to
north India. It occurs in tropical Himalayas. Sikkim to East Bengal, Assam,
Manipur and Khasi hiils.
4) Gnetum contractum: A scandent shrubs. It occurs in Travancore, Kerala,
Coonoon and Nilgiri hills.
5) Gnetum ula: It is large woody climber with scaly bark and swollen nodes. The
species is distributed along Eastern and Western Ghats.
Gnetum gnemon
Gnetum latifolium
Gnetum montanum
Gnetum ula
4. Sporophyte of Gnetum:
Gnetum resembles very much in its characteristics to an
angiosperm than a gymnosperm. Based on the studies of
58 characteristics, Gnetum shares more than 60% of the
characteristics with angiosperm and about 30%
characteristics with gymnosperm. Gnetum is easily
mistaken for a dicot plant unless it is in flowering or
fruiting stage. The plant body is differentiated into root,
stem and leaves.
5. 1. Root of Gnetum:
Gnetum shows a typical tap root system which is
profusely branched. The mature roots show normal
secondary growth.
Internal Structure:
Internally, the root of Gnetum resembles the root of
angiosperm. The root is differentiated into the outermost
layer epidermis, multilayered cortex and diarch vascular
cylinder. The cortex consists of polygonal or oval-
shaped parenchymatous cells containing starch grains.
The thick-walled fibre cells are often present in the
cortex. A single-layered endodermis encircles a
multilayered pericycle.
6. The primary vascular cylinder is diarch, radial and
exarch. The secondary growth in roots is of normal
type. The arcs of cambium form below the phloem
groups and above the xylem groups which join
together to form a cambium ring. The secondary
xylem consists of tracheids possessing uniseriate
bordered pits with conspicuous Bars of Sanio. The
vessels are also present.
The pits on the vessels are bordered or simple, small
and multiseriate with or without inconspicuous Bars
of Sanio. The xylem ray is composed of thin-walled
parenchymatous cells containing starch grains. The
phloem consists of sieve cells and parenchyma. The
periderm is formed due to the extrastelar secondary
growth.
7. 2. Stem of Gnetum:
External Morphology:
Almost all the species of Gnetum, except the tree type
like G. gnemon, exhibits two types of branches viz. dwarf
shoots or branches of limited growth and long shoots or
branches of unlimited growth. In climbing and scandent
species of Gnetum, the stem is articulated with prominent
joints.
The joint consists of two parts: one just above the node
and the other below the node and these two are separated
by an annular groove. In arboreal species such as G.
gnemon, the stem exhibits uniform type of branching.
8. The cells of the inner regions are referred to as spicular
cells . Many fibrous cells are often present which have
branched or unbranched pit canals. The cortex is
followed by endodermis and pericycle layers which are
not distinct. Next to pericycle, there is an endarch
siphonostele.
The vascular cylinder is comprised of 20-24 collateral,
open and endarch vascular bundles, arranged in a ring.
The vascular bundles are separated from one other by
wide primary medullary rays. The xylem consists of
tracheids and few vessels . The protoxylem of
tracheids have annular or spiral thickening and the
metaxylem have reticulate thickening with uniseriate
bordered pits. The phloem is composed of sieve cells
and phloem parechyma. Laticiferous elements are
often found in pith as well as in cortex.
9. Secondary Growth in Thickness:
In tree species like G. gnemon, the secondary growth is of
normal type. The fascicular cambium joins with
interfascicular cambium to form a complete cambium ring
that cuts off a continuous cylinder of secondary xylem
towards the inside and secondary phloem towards the
outside. The secondary xylem is produced much more than
the secondary phloem.
In climbing species (G. ula, G. africanum), the anomalous
secondary growth is noted. Initially, the stem shows
normal secondary growth. Later, several successive
cambium rings are formed in the cortex.
Thus, several extra- stellar rings of xylem and phloem are
formed which are separated into wedge-shaped bundles
because of medullary rays . Some of these accessory rings
remain incomplete and as a result, the vascular bundles
become concentric with regard to pith.
10. The periderm is also formed by the activity of phellogen
during the third or fourth year of growth of the stem.
The wood of Gnetum is composed of vessels, tracheids
and xylem parenchyma. The vessels are of different sizes
and have a single pore on their end walls . The tracheids
are much longer than the vessels and have bordered pits
on both of their radial and tangential walls. The xylem
parenchyma cells have simple pits. There are many uni- to
multiseriate vascular rays.
The secondary phloem consists of sieve cells and phloem
parenchyma. The companion cells are totally absent in
Gnetum, although some small cells are present near the
sieve tube.
The vascular rays are very large and multi- seriate which
appear boat-shaped in T.L.S. Occasionally, some short
biseriate or uniseriate rays are present. The ray cells are
thick-walled and pitted.
11. 3. Leaf of Gnetum:
External Morphology:
Gnetum exhibits leaf dimorphism bearing both the foliage leaves and scale leaves.
A dwarf shoot bears 9 to 10 foliage leaves, arranged in an opposite decussate
manner. The leaves are large, simple having an oval-shaped broad coriaceous
lamina with unicostate reticulate venation. The leaves are exstipulate, shortly
petiolate with entire margin. The leaf of Gnetum resembles a dicot leaf.
12. Internal Structure:
Anatomically, the leaves of Gnetum resemble those of
dorsiventral dicot leaves. The epidermis (both upper and
lower) has undulating walls, covered with thick cuticle. The
mesophyll is differentiated into palisade and spongy
parenchyma.
The palisade consists of single-layered compactly arranged
elongated cells. The spongy parenchyma is composed of
loosely arranged lobed cells. In addition, some spicular
cells, sclerotic cells, latex tubes and fibres are also present.
The vascular bundles are arranged in a curved in the midrib
region. Each bundle is of conjoint, collateral and endarch
type with an adaxial xylem and abaxial phloem. There are
distinct patches of stone cells outside the phloem.
The xylem is composed of vessels, tracheids and xylem
parenchyma, while the phloem consists of sieve cells and
phloem parenchyma. Transfusion tissue is present in the
petiole in association with vascular bundles.
13. Essay # 2. Reproduction:
Gnetum reproduces sexually. Gnetum is dioecious
and both the male and female strobili
(inflorescence) are compound. The inflorescence is
either axillary or terminal in position which occurs
singly or in groups. The inflorescence is composed
of a stout long axis with two opposite decussate,
connate bracts at the base and a series of cup-like
bracts called cupules or collars that are superposed
one above the other.
Male inflorescence
Female inflorescence
14. The strobilus becomes compact at young stage
because of the suppression of internodes. Thus,
the collars of a young strobilus appear to be
continuous . At maturity, the axis becomes
elongated and the collars get separated. There
are many rings of flowers in the axil of collars.
The collars are developed in acropetal
succession and the flowers are initiated as
mounds of meristematic cells from the lower
surface of a collar.
15. Male Strobilus:
The male strobilus is compound and has a long slender axis
bearing 10-25 whorl of bracts (collars). About 12-25 male
flowers are arranged in three to six rings above each collar .
A single ring of 7-15 imperfect female flowers or abortive
ovules is present just above the male flowers.
Male Flower:
A male flower consists of two unilocular anthers on a stalk
(antherophore) enclosed in a small sheathing perianth. The
stalk of the anther elongates rapidly at maturity pushing the
anther beyond the collars through a slit in the perianth.
16. Female Strobilus:
The female strobilus is very much similar to that of the male strobilus
in the young stage. Like male strobilus, the female strobilus consists of
an axis bearing several whorl of collars arranged one above the other. A
ring of 4-10 ovules (female flowers) is present above each collar. The
male flowers are not found in the female strobilus. The upper few
collars are devoid of ovules and are thus sterile.
Female Strobilus
17. Development of Male Gametophyte before Pollination:
Pearson view: The pollen grain is inapeturate and spherical, bounded by the two concentric
wall layers: the outer thick, spiny exine and the inner thin intine. The pollen nucleus divides
mitotically to produce a small lens-shaped prothallial cell and a large antheridiai initial. The
prothallial cell does not divide further and eventually degenerates. The antheridiail initial
divides to form an antheridiail cell and a tube nucleus. The antheridiail cell directly functions
as spermatogenous cell. The pollen grains are released from the microsporangium at this 3-
celled stage (one prothallial cell, an antheridiai or spermatogenous cell and a tube nucleus).
18. Thomson view (1961), the prothallial cell is not formed in Gnetum. He proposed
that the pollen nucleus cuts off a tube nucleus and a generative cell. The generative
cell again divides forming a stalk cell and a body cell. Thus, the pollen grains are
released at this 3-celled stage (tube nucleus, stalk cell and body cell).
19. Negi and madhulata View: According to Negi and Madhulata (1957) a small prothallial cell is
formed. But it never enters in to pollen tube. The other nucleus to form tube nucleus and
generative nucleus. The tube nucleus enters into the pollen tube. The generative nucleus divides
directly to form two male nuclei. According to this authors stalk cell and body cells are not
formed.
Tube nucleus
20. Development of Female Gametophyte:
At the initial stage, before the gametophyte
formation, the nucellar cells immediately below
the megaspore mother cell divide to form a tissue.
The cells of this tissue are arranged in radiating
rows. This tissue is termed as ‘pavement tissue’
which eventually gets absorbed and seems to be
nutritive in function.
There is a free nuclear division in the
coenomegaspore, as a result a large number of
free nuclei are formed (Fig. 1.77A). The number of
nuclei thus formed varies in different species, viz.
256 in G. gnemon, 512 in G. africanum and 1500 in
G. ula. At this stage, a large central vacuole appears
and the free nuclei lie in a thin film of cytoplasm
around the vacuole towards the periphery (Fig.
1.77B). Later, the nuclei in the peripheral
cytoplasm divide repeatedly.
21. At this stage, the upper part of the gametophyte surrounding a vacuole widens, while the
lower part of the gametophyte shows accumulation of cytoplasm. Thus, the gametophyte
becomes an inverted flask-shaped structure (Fig. 1.77C). The wall formation starts very
slowly from the chalazal end towards the micropylar end. Thus, the nuclei remain free at
the microphylar end even at the time of fertilisation.
The important characteristic in the female gametophyte of Gnetum is the absence of
archegonia. One to three nuclei of the gametophyte in the micropylar end enlarge several
times and accumulate dense cytoplasm around them. These large and densely cytoplasmic
cells are the eggs (Fig. 1.77B). It is important to note that all the eggs do not mature
simultaneously.
22. Ovule:
A single ovule represents a female flower. The ovule
is stalked in G. ula, but may be sub- sessile or even
sessile. The ovules are orthotropous, crassinucellate
(with massive nucellar tissue) and are protected by
three envelopes. The outer envelop which becomes
thickened and succulent at maturity is considered to
be the perianth corresponding to the perianth of male
flower.
The middle and the inner envelopes are actually the
integuments. Numerous laticiferous ducts and
sclerides are present in the perianth with some
epidermal stomata. The middle envelop is called the
outer integument which is anatomically similar to the
outer envelop. The inner envelop, i.e., the inner
integument, elongates far beyond the apical cleft of
the perianth and forms a long micropylar tube.
23. Anatomically, the inner integument is
different from the other two envelopes,
because neither sclerides nor stomata
develop in the inner integument. The
inner integument is free from the nucellus
except at the chalazal end.
Two sets of vascular bundles are formed,
of which the outer set passes to the
perianth and the inner set again divides
and one of its branches passes to the outer
integument and the other to the inner
integument. All the three envelopes of
ovules develop in acropetal manner. A
shallow pollen chamber is present at the
tip of the nucellus.
24. Pollination:
Gnetum is wind-pollinated. The pollen grains are dispersed from the anther and remain
suspended in the air for some time. At the free nuclear stage of the female gametophyte, the
nucellar beak in the ovule disorganises forming a viscous sugary liquid which comes out
through the microphyle in the form of a pollination drop. The pollen grains are caught in the
pollination drop.
Due to the drying off of the fluid, the pollen grains are sucked into the micropylar canal and
are finally collected in the pollen chamber. The mouth of the micropyle is then sealed from
the outer environment due to the development of flage (a circular rim or an umbrella-
shaped structure develops from the inner integument) and micropylar closing tissue (a tissue
develops by the proliferation of the inner epidermis of integument at the level of flage).
25. Fertilisation:
The pollen tube enters the female gametophyte and the male gametes
move ahead of tube nucleus (Fig. 1.77B). The pollen tube ruptures to
discharge the male gametes into the egg cell. The cell sheath of male cell
is left outside the egg cell. Usually one of the male nuclei fuses with the
egg nucleus and thus a zygote is formed. Sometimes, two male gametes
may fuse two different eggs if those eggs are in the vicinity of the pollen
tube.
26. Endosperm:
In gymnosperms, endosperms are cellular and haploid and are formed before fertilisation. However, in
Gnetum the development of endosperms starts before fertilization very slowly from lower part of the
gametophyte which eventually proceeds upward. After fertilization, the wall formation starts in such a
way that the cytoplasm divides into many multinucleate compartments (Fig. 1.78A). Later, the nuclei in
each cell fuse to form a single polyploid nucleus (Fig. 1.78B).
In this stage, the lower part of the gametophyte becomes cellular, while the upper part remains free
nuclear even after fertilization.Thus, the development of endosperm takes place even after fertilization.
There is a great variation in the development of endosperm in Gnetum. In some cases, the wall formation
starts either from the upper part or from the middle part of the gametophyte instead of the lower part and
the whole gametophyte may become cellular. Though some portions of the endosperms are formed after
fertilization, the characteristic triploid endosperm through double fertilization is, however, absent in
Gnetum.
27. Seeds:
Gnetum seeds are oval in shape and green to brown-red in colour. The seeds remain
covered with a three-layered envelop, of which outer is fleshy, middle is stony and
inner is pepary. The nucellus is used up and the embryo is embedded within the
endosperm. Gnetum shows one-year reproductive cycle where pollination, fertilisation
and development of embryo take place in one year.
The germination of seed is epigeal. The seeds of G. ula germinate after one year’s of
resting phase.