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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Such Pteridophytes are known as heterosporous and the phenomenon is known as heterospory.

Heterospory and Seed Habit in Pteridophytes | Botany

By sudden lowering of the temperature, on size of the microspores in the sporocarp of Marsilea increases by six times. In Selaginella Isoetes it is distinct before meiosis. Latest Most Read Most Cited Does the shape of forelimb long bones co-vary with grasping behaviour in strepsirrhine primates? 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:.

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Here one thing may be 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.

Here’s how it works: General Characters of Pteridophytes Words. The phenomenon of heterospory is of great biological significance on account of the following facts: Don’t already have babit Oxford Academic account? The origin of heterospory can be better discussed on the basis of evidences from paleobotany, developmental and experimental studies.

You could not be signed in. In all Selaginella species. Such Peridophytes are known as homosporous and this phenomenon is known as homospory. The two types of spores are microspores and megaspores.

The microsporangia contain srlaginella whereas megasporangia contain megaspores in them. Microspores are smaller in size and develop into the male gametophyte while the megaspores are large and develop into female gametophyte. Anumber of heterosporous genera belonging to the Lycopsida, Sphenopsida and Pteropsia were known in the late Devonian and early Carboniferous periods.

Development of protective layers and nutritive tissue around megasporangium. A seed is that ovule which contains an embryo developed as a result of fertilization. Seeds are traditionally defined by the possession of integuments. However, in megasporangium, a part of the sporogenous tissue degenerates they provide nutrition to growing habt megaspores.

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Though Selaginella as well as lower Spermatophytes shows homologies in their structure as follows: Citing articles via Web of Science Sign in via your Institution Sign in. Therefore, integuments cannot selagineella the evolutionary success of seed plants.

Plant Science 4 U. In the figure, Solid red circle indicates: In Selaginella rupestris and S.

Heterospory and Seed habit in Selaginella | Plant Science 4 U

Development of protective layers and nutritive tissue around megasporangium to some extend: Modification of distal end of megasporangium for pollen capture. Temporary suspension of growth of embryo i. Structure of Rhynia With Diagram Pteridophytes. According to modern pteridologists the heterospory is found in seven genera-Selaginella, Nabit, Marsilea, Salvinia, Azolla, Regnellidium and Pilularia.

The retention seev megaspore permanently inside the megasporangium has not been well established. During this period important heterosporous genera were Lepidocarpon, Lepidostrobus, Mazocarpon, Plaeuromeia, Sigillariostrobiis members of Lycopsid Calamocarpon, Calamostachys, Palaeostachys members of Sphenosida.

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