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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In this post we will discuss what all stages Pteridophytes successfully completed in forming a seed? In homosporous plants, the male and female gametes are formed in the same prothallus.
Palaeobotanical evidences show that the earlier vascular plants wert all homosporous and the heterosporous condition appeared subsequently in the lowermost upper Devonian. Temporary suspension of growth of embryo i. This is made possible by the development of pollination mechanism.
Development of seed with protective layers. Similar type of abortion of spores was also observed in Stauropteris Chaloner, Lepidocarpon and Calamocarpon.
Importance of Heterospory and Seed Habit of Ferns ( Words)
Under conditions of low light intensity, jn photosynthetic activity of Selaginella was retarted and it produced microsporangia. The phenomenon of heterospory is of great biological significance on account of the following facts: Microspores are smaller in size and develop into the male gametophyte while the megaspores are large and develop into female gametophyte.
A seed is that ovule which contains an embryo developed as pteridopbytes result of fertilization. Your email address will not be published.
Development of pollination mechanism. More Pteridophytes Lecture Notes.
In the figure, Solid red circle indicates: Such Pteridophytes are known as heterosporous and the phenomenon is known as heterospory.
What eeed the evolutionary significance of Heterospory?
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Such Peridophytes are known as homosporous and this phenomenon is known as homospory. Gametophytic tissue represented by the female gametophyte. They are differentiated into micro and megasporangia. The gametophytes of the ferns are, however dependent for their nutrition upon soil and environmental condition, whereas ij the case of Selaginella, as far as the nutrition of gametophytes is concerned they derive it from the sporophyte, and there they are more independent to the external condition than those of fems.
Difference between Microspores and Megaspores: Heterospory is the production of two or more types of spores. Land plants up to pteridophytes are homosporous. Evolution of the seed is one of the most crucial adaptations in Phanerogams for successful survival in terrestrial habitat. In Pteridophytesthese two spores are called as Microspores and Megaspores.
The chance of the survival of the independent gametophyte is very less. These species were C.
The sporangia show greater specialization than those of ferns. Plant Science 4 U.
It becomes quite evident that Selaginella has considerably advanced towards the seed habit in a few species, but its approach to the true seed is not complete due to the following features:.
Thus the chance of fertilizing an egg with the sperm of the same prothallus is very high. Most of pteridophyytes Pteridophytes produce one kind of similar spore. Difference between Microspores and Megaspores. Structure of Rhynia With Diagram Pteridophytes. As more nutrition becomes available to less number of spores, the surviving spore grow better, hence increase in their size.
What are the possible evolutionary events in the formation of seeds in land plants? The microsporangia contain microspores whereas megasporangia contain megaspores in them. The gradual development of seed habitat from heterosporous condition may be occurred in the following steps: Megaspore is protected by its wall also but not by an yabit. Retention and germination of megaspore pteridopgytes the megasporangium to some extend: In pteridophytes, further steps towards seed habit are lacking.
Here one thing may be noticed that the microspores develop male gametophytes whereas the heterospry the megaspores germinate into the female gametophytes which may also be called as microgametophytes and megagametophytes. Advantages and Disadvantages of Vegetative Propagation.
Importance of Heterospory and Seed Habit of Ferns (581 Words)
What are its significances? The ptrridophytes evolved species, i. Learning and Loving Plants. You must be logged in to post a comment. Moreover, they have a continuous supply of food material from the diploid sporophytic plant.
Describe the advantages of seed habitat.