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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Of the four, only one is retained ensuring enough space, food and greater chance of developing into a healthy female gametophyte. What is Vegetative Propagation? Permanent retention of megaspore within the megasporangium. Parent sporophytic tissue represented by integuments and nucellus.
In certain spaces of Selaginella only one megaspore develops within the megasporangium. In Selaginella, there is remarkable approach to the seed habit, on account of the following important features:.
Reduction to a single functional megaspore per sporangium. The heterospory also facilitated the sex differentiation in Pteridophytes. Such Peridophytes are known as homosporous and this phenomenon is known as homospory. Each microsporangium contains a large number of microspores whereas each megasporangium contains usually only four megaspores. In Isoetes there are only megaspores in megasporangium. The homosporous Pteridophytes show exosporic outside the spore wall gametophytic development.
The two types of spores are microspores and megaspores. The endosporic gametophytes are independent of the external harsh environmental conditions. No siphonogamy, therefore water is essential for fertilization.
When one kind of spores are present, e. Heterospory produced the first endosporic inside the spore wall type of gametophyte development in land plants. This is made possible by the development of pollination mechanism. Development of seed with protective layers. In Pteridophytesthese two spores are called as Microspores and Megaspores. Megaspore is protected by its wall also but not by an integument. Advantages and Disadvantages of Vegetative Propagation. A seed is that ovule which contains an embryo developed as a result of fertilization.
The indication of the starting of pollination mechanism is observed in Selaginella where a temporary retention of the female gametangia within the megasporanigum is evident.
In most of the heterosporous plants, the gametophyte is restricted to very few cells.
Importance of Heterospory and Seed Habit of Ferns ( Words)
Development of an embryo sac within the sporangium. However, in megasporangium, a part of the sporogenous tissue degenerates they provide nutrition to growing sporocytes megaspores. Among Pteridophytes, Selaginella rupestris is the most successful species that completed first four steps towards seed habit.
In heterosporous plants, the male and female gametangia are separated both in time and space. The next big step in evolution was heterospory or formation of two different types of spores, the smaller ones called microspores and the larger ones known as megaspores. Palaeobotanical evidences show that the earlier vascular plants wert all homosporous and the heterosporous condition appeared subsequently in the lowermost upper Devonian.
Importance of Heterospory and Seed Habit of Ferns (581 Words)
Retention and germination of megaspore within the megasporangium to some extend: During this period hererospory heterosporous genera were Lepidocarpon, Lepidostrobus, Mazocarpon, Plaeuromeia, Sigillariostrobiis members of Lycopsid Calamocarpon, Calamostachys, Palaeostachys members of Sphenosida.
Anumber of heterosporous genera belonging to the Lycopsida, Sphenopsida and Pteropsia were known in the late Devonian and early Carboniferous periods. Seed is the ripened ovule with integuments formed after fertilization.
Difference between Bryophytes and Pteridophytes. What are the advantages of heterosporous condition over homospory?
Heterospory and Seed habit in Pteridophytes (Ferns) | Plant Science 4 U
Moreover, there is no evidence to prove the development of seed habitat from homosporous condition. Successful to some extend. This is a question and answer forum for students, teachers and general visitors for exchanging articles, answers and notes. As more nutrition becomes available to less number of spores, the surviving spore grow better, hence increase in their size.
In homosporous plants, the male and female gametes are formed in the same prothallus. There is reduction to one megaspore in some species, e. Newer Post Older Post Home. The condition of the production of two kinds of dissimilar spores, differing in shape and size in the same species, is termed Heterospory.
What are its significances? In this article we will discuss about heterospory and seed habit in pteridophytes. Development of pteridophyttes connection between the megasporangial wall and the megaspores.
The exosporic gametophytes have to find the nutrients from the external environment. The chance of the survival of the independent gametophyte is very less. 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 they derive it from the sporophyte, and there they are more independent to the external condition than those of fems.
Microspores are small sized spores produced in large numbers inside the microsporangium. Various steps involved in the evolution of seed habit are as follows: General Characters of Pteridophytes Words.