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 phenomenon of heterospory is of great biological significance on account of the following facts: In most of the heterosporous plants, the gametophyte is restricted to very few cells.
The heterospory also facilitated the sex differentiation in Pteridophytes. Range of thallus structure in Algae.
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The condition of Heterospory in Selaginella constitute one of the most important phases in the evolution of the plants. Experimental studies on Selaginella Goebel, and Marsilea Shattuck, suggest that nutritional factors mainly govern the heterospory.
Development of an embryo sac within the sporangium. Here one thing may be noticed that the microspores develop male gametophytes whereas the megaspores the megaspores jeterospory into the female gametophytes which may also be called as microgametophytes and megagametophytes.
What are the possible evolutionary ptsridophytes in the formation of seeds in land plants? The formation of seed is one of the greatest evolutionary vents ppteridophytes the phylogeny of seed plants. Types of Stelar System and its Evolution in Pteridophytes.
Here’s how it works: Seeds have many advantages than spores: The production of two types of spores with different sexuality was first evolved in Pteridophytes. Thus, the heterosporous sefd is considered as precondition for the seed habitat.
It is the greatest adaptation of land plants to ensure its reproductive success and survival. Temporary suspension of growth of embryo i.
Anybody can ask a question Anybody can answer The best answers are voted up and rise to the top. This is made possible by the development of pollination mechanism. Microspores are small sized spores produced in large numbers inside the microsporangium. As more nutrition becomes available to less number of spores, the surviving spore grow better, hence increase in their size. Difference between Microspores and Megaspores: In pteridophytes, further steps towards seed habit are lacking.
Heterospory and Seed Habit in Pteridophytes | Botany
Here, the megaspore remains within the sporangium; it itself fertilizes and this way for the first time the gametophyte of Selaginella shows complete dependence of the gametophyte upon sporophyte as in angiosperms. You may also like…. In the case of homospory the sex may be differentiated only at the gametophytic stage, but here the sex may be differentiated even at the sporophytic stage by the presence of small and large sized microspores which produce antherozoids and eggs respectively.
Retention and germination of megaspore within the megasporangium. Development of seed dispersal mechanism. Such Pteridophytes are known as heterosporous and the phenomenon is known as heterospory.
Importance of Heterospory and Seed Habit of Ferns (581 Words)
Developments for the availability of sufficient nutrition. In Isoetes there are only megaspores in megasporangium.
Development of protective layers and nutritive tissue around megasporangium. What are its significances? In heterosporous Pteridophytes the development of micro and megasporangia follow the same pattern. Palaeobotanical evidences show that the earlier vascular plants wert all homosporous and the heterosporous condition appeared subsequently in the lowermost upper Devonian.
This reduces the chance of self-fertilization and increases the chance of variability in the progenies. Meaning, General Characters and Affinities. Successful to some extend. Microspores are smaller in size and develop into the male gametophyte while the megaspores are large and develop into female gametophyte.
Development of znd connection between the megasporangial wall and the megaspores.
In microsporangium all the microspores are functional while in magasporangium one megaspore is functional and rest degenerate. They have identical organization but for their size. In Marsilea 64 microspores and 64 megaspores are formed after meiosis in microsporangium and megasporangium respectively.
Thus, the endosporic development is a good starting point for the survival of the young embryo. The retention and germination of the fertilization of the egg and embryo formation, which is still within germinating megaspore. Havit seed is actually an integumented megasporangium.
You must be logged in to post a comment. The offspring sporophyte represented by the embryo. The gametophytes of the ferns are, however dependent for their nutrition upon soil and environmental condition, whereas in the case of Selaginella, as far as the nutrition of gametophytes is concerned they pteridiphytes it from the sporophyte, and there they are more independent to the external condition than those of fems.
However, there are some Pteridophytes which produce two different types of spores differing in size, structure and function. Give the names few Pteridophtyes which shows heterosporous condition. In homosporous Pteridophytes, the sex differentiation takes place only during the development of antheridia or archegonia.
Development of only one megaspore per megasporangium for example, in Selaginella monospora, S. What is the evolutionary significance of Heterospory?
They are male spores which on germination produce male gametophyte. The seed represents three generations: