1. GOVT. SUKHRAM NAGE
COLLEGE NAGRI
DIST.DHAMTARI C.G.(493778)
Session 2023-24
Paper IV-
BRYOPHYTA,PTERIDOPHYTA AND
GYMNOSPERM
Topic-Heterospory and
origin of seed habit
Date-
Guided by-
Asst.Prof.L.Rathiya
Presented
by-
Kirti lata Sahu
M.Sc I Sem
Botany
2. Content
• Introduction
• Defination
• Character of heterospory
• Origin of heterospory
• Importance of heterospory
• Seed habit in pteridophyta
• Origin of seed habit
• Origin and development of ovule
• Importance of seed habit
• Conclusion
• Reference
3. Introduction
• In the silurian period- first terrestrial
plant
• Ferns and pteridophytes came into
existence
• All these are seedless
• Reproduction – by different types of
spores
• After sexual reproduction,zygote
formed but seed not formed
• Pteridophytic plant-
Selaginella,along with the
development of heterospory traits
related to seed habit emerged.
• Heterospory is considered to be a
pre-requisite to seed formation.
4. Defination
• Hetero means ‘Different’
• Production of two types of spores
in plants of the same species
• Differ in size,structure,number,and
developme -nt pattern.
• Such spores- heterospores
• Plant –heterosporus plant
• Found in vascular cryptogames
Fig.L.S.of cone of
Selaginella
5. On the basis of number,size and Structure of spores
2 types of plants
Homosporous plants Heterosporus Plants
Homospory - presence of one type of sporangai
and spores on same plant
Ex.- Lycopodium,Equisetam etc
Characters- development eusporngiate type.
Similar in size
Fig. Lycopodium
6. Heterospory
• Two kinds of spores
• Different in size etc.
• Small sized spores- microspores
and sporangia they are produced
–microsporangium
• Larger in size- megaspores and
sporangia they are produced –
megaaporangium
• Germination of microspores-
male gametophyte
• Gerrmination of megaspores –
female gametophyte
7. • A/d to Rashid (1976) only 9 generaof
pterodophytes are heterosporous
Fig.Regnellidium Fig.Marsilea Fig.Salvinia Fig.Azolla
Fig.Selaginella Fig.Platyzoma Fig.Isoetes
Fig.Pilularia Fig.Stylites
8. Charactersof heterospory
• Development of spores-
Leptosporangiate type
• Two types of spores
• Microspores are more in
number
• Megaspores are less in
number
• Due to getting sufficient
• nutrition , their size
become larger.
Fig.Microsporangium
Fig.Megasporangium
9. Origin of heterospory
• It is universally accepted that
homosporous condition is
primitive and heterospory is
derived.
• On the basis of evidences from
1. Palaeobotanical evidences :-
2.Evidences from developmental
studies
3.Evidences from experimental
studies
10. Importance of Heterospory
• Differentiation of gametophytes
• Most important – development
of seed habit
• Produced endosporic
gametophytes
• Endosporic development provides
starting point for the young
embryo.
• Because of heterospory plants
beome free to grow in varied
environmental conditions,instead
of only aquatic surroundings.
11. Seed Habit in Pteridophytes
• The adoption if heterospory and
the retention and germination of
a single megaspore within
megasporangium to form a
female gemetophyte ,led to the
phenomenon of “seed habit”.
• Heterospory is a very necessary
and complete condition for seed
formation.
12. Origin of seed habit
• Heterospory
• Development of only one
megaspore in each
megasporangium.
• Reduction in the size of male
gametophyte.
• Formation of an additional covering
called integument.
• The megaspore present inside
megasporangium throughout its life
.
• Nutrition for fetal development
• Elaboration of apical part of
nucellus to receive microspores or
pollen grains.
13. To clarify the evolution towards seed habit
of pteridophyta we take example of
selaginella
• The occurrence of the phenomenon of
heterospory.
• Germination of megaspore inside
megasporangium.
• Development of only one
megaspore inside megasporangium.
• Retention of megaspore
inside megasporangium throughout its life.
• Ex.-S.rupestris ,S.monospora etc.
• All these symptoms clears the
seed habit development in
seleginella species but it could not
become a complete seed in the true sense.
Fig.S.monospora
Fig.S,rupestris
14. Origin and development of ovule
• The main characteristic of spermatophytes
is their production of seeds.
• The origin and development of seeds
occurs only after the maturity of the ovule.
• Many theories are given to undrestand
origin and development of ovule.
Telome cocept- A/d to Smith (1959)
Long(1960), and Andrews(19610)
• The first stage of development
is represented by- Rhynia type branching
telome
• Some of them being fertile
bearing terminal sporangia.
15. • First of all decrease in the number of
megaspores.
• Upper part of megasporangium increased
in length.
• The structure that captures pollen grains
was created
• Integument developed- result of
changes in sterile telomes
• Partial fusion of sterile telomes-
resulted development of cupule-like
structure
• Cupule initially independent
of the nucellus,but later became
attached basal part of cupule.
• Observed in Genomosperma latens
• By joining together of these sterile
telomes,second integument developed-
ex. In Genomosperma scotica.
• Integument joined with nucellus- in
calathospermum scoticum.
Fig.Rhynia
16. • Due to extinction of lobes
and reduction in the number
of anterior lobes
• Joining together of integuments-
micropyle developed
• The work of catching
pollen grains started through
micropyle instead of anterior part of body
• The number of lobes of cupule
and integuments further decreased.
• Ultimately both integuments fused
Thus,as a result of all processes and various
successive stages.The Telome theory gained
immense recognition because most of the
availble fossile records confirm this theory.
Fig. Various stages of
origin of seed
17. Importance of seed habit
• Protect the embryo from harsh
environmental conditions.
• Provide nourishment
• Parental care to the developing
embryo
• Capability of dormancy
• Effective dispersal
18. Conclusion
• We can conclude that there is a
connecting link between
heterosporus condition and
formation of seed habit.
• Heterospory of seleginella plays
significant role in the
development of seed habit and
finally from this seed-habit
evolution of seed might have
taken place in higher plants.
19. Reference
• Book name- Botany
Writer name- singh pandey
jain
publication- Rastogi
publication
• By Dr.Ankit Kumar Singh
