Heterospory and seed habit

Heterospory

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

20. Thank You