Heterospory and Origin and Evolution of Seed Habitat in Land Plants – Pteridophytes. Evolutionary Significance of Heterospory and Seed Development in. feature of the seed habit, the enclosure of the female spore; ” Der. Embryosack der s]iorous Pteridophytes there may be little or no difference in the size. Heterospory and seed habit. Reference * Botany for degree students – pteridophyta by:Vasishtha B.R Sinha A.K. Singh V.P *
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The highest evolved species, i. The homosporous Pteridophytes show exosporic outside the spore wall gametophytic development. From the above observations it is concluded that the life history of Selaginella approaches heteropsory seed habit because of the following features:. In homosporous Pteridophytes, the sex differentiation takes place only during the development of antheridia or archegonia.
Microspores ans small sized spores produced in large numbers inside the microsporangium. Some of these forms even arrived at the seed stage.
In Marsilea 64 microspores and 64 megaspores are formed after meiosis in microsporangium and megasporangium respectively.
They are differentiated into micro and megasporangia. Rounded red circles indicates different steps. Successful in some species. Thus, the heterosporous condition is considered as precondition hetedospory the seed habitat.
Importance of Heterospory and Seed Habit of Ferns (581 Words)
The sporangia show greater specialization than those of ferns. General Characters of Pteridophytes Words.
The heterospory also facilitated the sex differentiation in Pteridophytes. Of the four, only one is retained ensuring enough space, food and greater chance of developing into a healthy female gametophyte.
The microsporangia contain microspores whereas megasporangia contain megaspores in them. The permanent retention of the megaspore within pyeridophytes megasporangium has not become established. Many spore mother cells disintegrate to form nutritive tissue. The gametophytic generation is a weak link between the sporophyte and seed in the life cycle of terrestrial plants. Moreover, there is no evidence to prove the development of seed habitat from homosporous condition.
Even though, the condition of hzbit is now represented only by eight living species of Pteridophytes, they are Selaginella, Isoetus, Marsilea, Salvinia, Azolla, Pilularia, Regnellidium and Platyzoma.
In most of the heterosporous plants, the gametophyte is restricted to very few cells. Reduction to a single functional megaspore per sporangium. Reduction to a single functional megaspore per sporangium: The phenomenon of Heterospory is of great biological advantage because of the fact that a large megaspore which contains female gametophyte derives its food from the sporophyte, and is independent of the external conditions as might interfere with the growth of a free living gametophyte.
Retention and germination of megaspore within the megasporangium to some extend: By sudden lowering of the temperature, the size of the microspores in the sporocarp of Marsilea increases by six times.
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Heterospory and Seed Habit in Pteridophytes | Botany
One of the most important advantages of heterospory is the formation of seed habitat. This reduces the chance of self-fertilization and increases the chance of variability in the progenies. Differentiate Megaspores and Microscpores. Land plants up to pteridophytes pteridolhytes homosporous.
Development of seed with protective layers. Under conditions of low light intensity, the photosynthetic activity of Selaginella was retarted and it produced microsporangia. Difference between Microspores and Megaspores: Range of thallus structure in Algae. The origin of heterospory can be better discussed on the basis of evidences from paleobotany, developmental and experimental studies. They are male spores which on germination produce male gametophyte.
The an types of spores are microspores and megaspores. The heterospory also reduced the size of gametophytic generation. Difference between Bryophytes and Pteridophytes. These two types of spore differ hdterospory their formation, structure and most importantly its functions and sexuality. Seed is pterivophytes ripened ovule with integuments formed after fertilization. Meaning, General Characters and Affinities. In Selaginella, there is remarkable approach to the seed habit, on pterirophytes of the following important features:.
It thus forms better starting point for the new embryo, than an independent green prothallus which has to manufacture its own food.
According to Rashid only 9 genera of Pteridophytes are heterosporous. This is a question and answer forum for students, teachers and general visitors for exchanging articles, answers and notes.
What are the advantages of heterosporous condition over homospory? Parent sporophytic tissue represented by integuments and nucellus.
Such Peridophytes are known as homosporous and this phenomenon is known as homospory.