HETEROSPORY AND SEED HABIT IN PTERIDOPHYTES PDF

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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Heterospory and Seed Habit in Pteridophytes | Botany

From the above observations it is concluded that the life history of Selaginella approaches towards seed habit because of the following features:. In heterosporous Pteridophytes the development of micro and megasporangia follow the same pattern. The exosporic gametophytes have to find the nutrients from the external environment. This summarize the successful steps of Pteridophytes towards seed habit.

During this period important heterosporous genera were Lepidocarpon, Lepidostrobus, Mazocarpon, Plaeuromeia, Sigillariostrobiis members of Lycopsid Calamocarpon, Calamostachys, Palaeostachys members of Sphenosida.

The differentiation of microspores and megaspores and their dependence seex the sporophyte has certain advantages. In the figure, Solid red circle indicates: The production of two types of spores with different sexuality was first evolved in Pteridophytes.

The gradual development of seed habitat heherospory heterosporous condition may be occurred in the following steps: The phenomenon of heterospory becomes distinct either before or after meiosis. These two types of spore differ in their formation, structure and most importantly its functions and sexuality.

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In Selaginella erythropus megasporangium contains only one megaspore which is functional. Difference between Bryophytes and Pteridophytes.

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Seed is the ripened ovule with integuments formed after fertilization. In most of the heterosporous plants, the gametophyte is restricted to very few cells.

Megaspore pteridophyted protected by its wall also but not by an integument. The origin of heterospory can be better discussed on the basis of evidences from paleobotany, developmental and experimental studies. Here one thing may be noticed that the microspores develop male gametophytes whereas the megaspores the megaspores germinate into hrterospory female gametophytes which may also be called as microgametophytes and megagametophytes.

They have identical organization but for their size. Parent sporophytic tissue represented by integuments and nucellus. Among Pteridophytes, Selaginella rupestris is the most successful species that completed first four steps towards seed habit. Seeds have many advantages than spores: No siphonogamy, therefore water is essential for fertilization.

When one kind of spores are present, e. The endosporic gametophytes are independent of the external harsh environmental conditions. In this article we will discuss about heterospory and seed habit in pteridophytes.

It has been suggested that heterospory arose due to degeneration of some spores in a few sporangia. The retention and germination of the fertilization of the egg and embryo formation, which is still within germinating megaspore. By sudden lowering of the temperature, the size of the microspores in the sporocarp of Marsilea increases by six times. You may also like….

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In certain spaces of Selaginella only one megaspore develops within the megasporangium. In this post we will discuss what all stages Pteridophytes successfully completed in forming a seed? This reduced the chance of genetic variability among homosporous plants.

Similar type of abortion of spores was also observed in Stauropteris Chaloner, Lepidocarpon and Calamocarpon. The megaspore usually germinates within the megasporangium and is not shed for a time which may vary from species to heeterospory. Gametophytic tissue represented by the female gametophyte.

Heterospory and Seed Habit in Pteridophytes | Botany

Development of an embryo sac within the sporangium. They are male spores which on germination produce male gametophyte. In order to overcome this problem, the female gametophyte is permanently retained in the megasporangium.

As more nutrition becomes available to less number of spores, the surviving spore grow better, hence increase in their size.

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