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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Meaning, General Characters and Affinities. Leave a Reply Cancel reply Your email address will not be published. Newer Post Older Post Home. Each microsporangium contains a large number of microspores whereas each megasporangium contains usually only four megaspores.
According to modern pteridologists the heterospory is found in seven genera-Selaginella, Isoetes, Marsilea, Salvinia, Azolla, Regnellidium and Pilularia. Thus, the endosporic development is a good starting point for the survival aand the young embryo.
Heterospory and Seed habit in Pteridophytes (Ferns) | Plant Science 4 U
The endosporic gametophytes are independent of the external harsh environmental conditions. The formation of seed is one of the greatest evolutionary vents in the phylogeny of seed plants.
Under conditions of low light intensity, the photosynthetic activity of Selaginella was retarted and it produced microsporangia.
What is the evolutionary pteriodphytes of Heterospory? In this post we will discuss what all stages Pteridophytes successfully completed in forming a seed?
Here’s how it works: Retention and germination of megaspore within the megasporangium to some extend: Temporary suspension of growth of embryo i. These two types of spore differ in their formation, structure and most importantly its functions and sexuality.
Reduction to a single functional megaspore per sporangium: Sedd gradual development of seed habitat from heterosporous condition may be occurred in the following steps: Stelar Evolution in Pteridophytes. In angiosperms, it is retained. Difference between Bryophytes and Pteridophytes. In the case of homospory the sex may be differentiated only at the gametophytic stage, but here the sex may be differentiated even at the sporophytic stage by the presence of small and large sized microspores which anr antherozoids and eggs respectively.
Moreover, there is no evidence to prove the development of seed habitat from homosporous condition. Advantages and Disadvantages of Vegetative Propagation.
Importance of Heterospory and Seed Habit of Ferns ( Words)
Microspores are small sized spores produced in large numbers inside the microsporangium. In most of the heterosporous plants, the gametophyte is restricted to very few cells. This is made possible by the development of pollination mechanism. They have identical organization but for their size. Production of two types of spores. Types of Stelar System and its Evolution in Pteridophytes. You must be logged in to post a comment.
One of the most important advantages of heterospory is the formation of seed habitat. There is reduction to one megaspore in some species, e. The offspring sporophyte represented by the embryo.
In order to overcome this problem, the female gametophyte is permanently retained in the megasporangium. Retention of megaspore inside megasporangium either till the formation of female gametophyte or even after fertilization.
Importance of Heterospory and Seed Habit of Ferns (581 Words)
Differentiate Megaspores and Microscpores. Thus, the heterosporous condition is considered as precondition for the seed habitat. Describe the advantages of seed habitat. According to Williamson and Scot two species of Calamostachys form the initial stage that might lead to the heterospory.
The phenomenon of heterospory becomes distinct either before or after meiosis. In Marsilea 64 microspores and 64 megaspores are formed after pteridophyfes in microsporangium and megasporangium respectively. No siphonogamy, therefore water is essential for fertilization. In heterosporous Pteridophytes the development of micro and megasporangia follow the same pattern.