EVOLUTION OF SEED HABIT IN SELAGINELLA PDF
PDF | Summary The origin of the seed-plant life history, and subsequent should be considered two independent, fundamentally distinct evolutionary problems. Historical biogeography of the ancient lycophyte genus Selaginella: Early. Selaginella largely upon the basis of endosperm development, without regard to great diversities in habit and anatomical details. The association may be. The highest evolved species, i.e., S. apoda has advanced almost upto the In Selaginella, there is remarkable approach to the seed habit, on account of the.
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Evidence for a complex evolutionary history of mound building in the Australian nasute termites Nasutitermitinae. Retention of megaspore inside megasporangium either till the formation of female gametophyte or even after fertilization.
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 hqbit of a free living gametophyte.
Importance of Heterospory and Seed Habit of Ferns ( Words)
In the figure, Solid red circle indicates: In all Selaginella species. Microspores are haabit in size and develop into the male gametophyte while the megaspores are large and develop into female gametophyte.
The phenomenon of heterospory is of great biological significance on account of the following facts: In Isoetes there are only megaspores in megasporangium. You do not currently have access to this article.
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In Selaginella rupestris and S. When one kind of spores are present, e. Close mobile search navigation Article navigation. It thus forms evolutio starting point for the new embryo, than an independent green prothallus which has to manufacture its own food. Development of an embryo sac within the sporangium. Don’t have an account? The condition of Heterospory in Selaginella constitute one of the most important fo in the evolution of the plants.
In Marsilea 64 microspores and 64 megaspores are formed after meiosis in microsporangium and megasporangium respectively.
Wind-pollination means the propagule is vulnerable to pathogens that mimic pollen, and pathogen pressures may have contributed to some seed characters. Strong, but incomplete, mate choice discrimination between two closely related species of paper wasp. This article is also available for rental through Selavinella. Such Peridophytes are known as homosporous and this phenomenon is known as homospory.
In heterosporous Pteridophytes the development of micro and megasporangia follow the same pattern. You must be logged in to post a comment. Development of protective layers and nutritive tissue around megasporangium to some extend: 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.
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The phenomenon of heterospory becomes distinct either before or after meiosis. Citing articles via Web of Science Abstract The evolution of the seed is one of the major events in the history of land plants. In Selaginella erythropus megasporangium contains only one megaspore which is functional.
In the last post, we discussed in detail the tendency of Pteridophytes towards seed habit. What is Vegetative Propagation? Related articles in Web of Evllution Google Scholar. To purchase short term access, please sign in to your Oxford Academic account above. Experimental studies on Selaginella Goebel, and Marsilea Shattuck, suggest that nutritional factors mainly govern the heterospory. This represents an increase in efficiency over Pteridophytic reproduction.
In this article we will discuss about heterospory and seed habit in pteridophytes. The highest evolved species, i.
Heterospory and Seed habit in Selaginella | Plant Science 4 U
However, there are some Pteridophytes which produce two different types of spores differing in size, structure and function. According to modern pteridologists the heterospory is found in seven genera-Selaginella, Isoetes, Marsilea, Salvinia, Azolla, Regnellidium and Pilularia.
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Heterospory and Seed Habit in Pteridophytes | Botany
However, in megasporangium, a part of the sporogenous tissue degenerates they provide nutrition to growing sporocytes megaspores. Reduction to a single functional megaspore per sporangium: From the above observations it is concluded that the life history of Selaginella approaches towards seed habit because of the following features:.
On is protected by its wall also but not by an integument. Among Pteridophytes, Selaginella rupestris is the one species that is very close to seed selahinella.
During this period important heterosporous genera were Lepidocarpon, Lepidostrobus, Mazocarpon, Plaeuromeia, Sigillariostrobiis members of Lycopsid Calamocarpon, Calamostachys, Palaeostachys members of Sphenosida.