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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According to Williamson and Scot two species of Calamostachys form the initial stage that might lead to the heterospory.

From the above observations it is concluded that the life history of Selaginella approaches towards seed habit because of the following features:. Here’s how it works: This represents an increase in efficiency over Pteridophytic reproduction. Related articles in Web of Science Google Scholar. Such Pteridophytes are known as heterosporous and the phenomenon is known as heterospory. Though Selaginella as well as lower Spermatophytes shows homologies in their structure as follows: By sudden lowering of the temperature, the size of the microspores in the sporocarp of Marsilea increases by six times.

Importance of Heterospory and Seed Habit of Ferns (581 Words)

In microsporangium all the microspores are functional while in magasporangium one megaspore is functional and rest degenerate. These are the basic requirements for seed habit: Retention of megaspore inside megasporangium either till the formation of female gametophyte or even after fertilization. It has been suggested that heterospory arose due to degeneration of some spores in a few sporangia. The evolution of the seed is one of the major events in the history of land plants.

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Temporary suspension of growth of embryo i. Plant Science 4 U. Sign in via your Institution Sign in. Don’t have an account? In all Selaginella species. Abstract The evolution of the seed is one of the major events in the history of land plants.

Heterospory and Seed habit in Selaginella | Plant Science 4 U

Range of thallus structure in Algae. Most users should sign in with their email address. Oxford University Press is a department of the University of Oxford. Don’t already have an Oxford Academic account? This article is also available for rental through DeepDyve. However, there are some Pteridophytes which produce two different types of spores differing in size, structure and function.

Our major conclusion is that most characters are a direct consequence of the origin of heterospory and of natural selection for propagules with larger food reserves.

Importance of Heterospory and Seed Habit of Ferns ( Words)

The microsporangia contain microspores whereas megasporangia contain megaspores in them. Many spore mother cells disintegrate to form nutritive tissue.

Here one thing may evoluyion noticed that the microspores develop male gametophytes whereas the megaspores the megaspores germinate into the female gametophytes which may also be called as microgametophytes and megagametophytes. Gymnospermsheterosporyintegumentspollinationseed habit. You could not be signed in.

Sign In Forgot password? The retention of megaspore permanently inside the megasporangium has not been well established. The permanent retention of the megaspore within the megasporangium has not become established. 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.

The effect of a flower-dwelling predator on a specialized pollination system. Reduction to a single functional megaspore per sporangium: Each microsporangium contains a large number of microspores whereas each megasporangium contains usually only four megaspores.

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Types of Evoolution System and its Evolution in Pteridophytes. Meaning, General Characters and Affinities. The condition of the production of two kinds of dissimilar spores, differing in shape and size in the same selafinella, is termed Heterospory. In the figure, Solid red circle indicates: 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 selaginlla derive it from the sporophyte, and there they are more independent to the external condition than those of fems.

Retention and germination of megaspore within the megasporangium. Strong, but incomplete, mate choice discrimination between two evolktion related species of paper wasp. habti

As more nutrition becomes available to less number of spores, the surviving spore grow ecolution, hence increase in their size. You do not currently have access to this article.

In this article we will discuss about heterospory and seed habit in pteridophytes.

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Palaeobotanical evidences show that the earlier vascular plants wert all homosporous and the heterosporous condition appeared subsequently in the lowermost upper Devonian. 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 fvolution features:. Evidence for a complex evolutionary history of mound building in the Australian nasute termites Nasutitermitinae.

Development of only one megaspore per megasporangium for example, in Selaginella monospora, S.

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