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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When one kind of spores are present, e. Thus the chance of fertilizing an egg with the sperm of the same prothallus is very high. The microsporangia contain microspores whereas megasporangia contain megaspores in them. The chance of the survival of the independent gametophyte is very less. In homosporous Pteridophytes, the sex differentiation takes place only during the development of antheridia or archegonia. One of the most important advantages of heterospory is the formation of seed habitat.

Development of organic connection between the megasporangial wall and the megaspores. Development of seed with protective layers.

Formation of protective layers integuments around the megasporangium. Advantages and Disadvantages of Vegetative Propagation. The phenomenon of heterospory becomes distinct either pteridoohytes or after meiosis. The gametophytic generation is a weak link between the sporophyte and pteridophytss in the life cycle of terrestrial plants. The seed is actually an integumented megasporangium. In the figure, Solid red circle indicates: But In Selaginella, nutritive tissue called tapetum is present.


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Under conditions of low light intensity, the photosynthetic activity of Selaginella was retarted and it produced microsporangia. Developments for the availability of sufficient nutrition.

It thus forms better starting pteridophgtes for the new embryo, than an independent green prothallus which has to manufacture its own food.

Heterospory and Seed habit in Pteridophytes Ferns. These two types of spore differ in their formation, structure and most importantly its functions and sexuality. According to modern pteridologists the heterospory is found in seven genera-Selaginella, Isoetes, Marsilea, Salvinia, Azolla, Regnellidium and Pilularia. Some of these forms even arrived at the seed stage. These species were C. Most of the Pteridophytes produce one kind of similar spore.

Megaspores are comparatively large spores produced in limited numbers 1 to 4 inside the megasporangium. Stelar Evolution in Pteridophytes. Successful to some extend. Thus, the heterosporous condition is considered as precondition for the seed habitat. Development of pollination mechanism. Land plants up to pteridophytes are homosporous. Reduction to a single functional megaspore per sporangium: This is made possible by the development of pollination mechanism.

During this period important heterosporous genera were Lepidocarpon, Lepidostrobus, Mazocarpon, Plaeuromeia, Sigillariostrobiis members of Lycopsid Calamocarpon, Calamostachys, Palaeostachys members of Sphenosida. The hwbit usually germinates within the megasporangium and is not shed for a time which may inn from species to species. The heterospory also facilitated the sex differentiation in Pteridophytes.

While in megasporangia most of the spore mother cells degenerate but in microsporangia only a few mother cells are disorganize.


Heterospory and Seed habit in Pteridophytes (Ferns) | Plant Science 4 U

Leave a Reply Click here to cancel reply. Production of singe megaspore per megasproangium.

The sporangia show greater specialization than those of ferns. Plant Science 4 U. Permanent ptetidophytes of megaspore within the megasporangium. The heterospory also reduced the size of gametophytic generation. Palaeobotanical evidences show that the earlier vascular plants wert all homosporous and the heterosporous condition appeared subsequently in the lowermost upper Devonian. 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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It is the greatest adaptation of land plants to ensure its reproductive success and survival. The phenomenon of heterospory is of great biological significance on account of the following facts: General Characters ppteridophytes Pteridophytes Words.

Range of thallus structure in Algae. Thus, heteorspory endosporic development is a good starting point for the survival of the young embryo. Learning and Loving Plants. In Pteridophytesthese two spores are called as Microspores and Megaspores.

More Pteridophytes Lecture Notes. Difference between Microspores and Megaspores: The retention of megaspore permanently inside the megasporangium has not been well established.