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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Various steps involved in the evolution of seed habit are as follows: The offspring sporophyte represented by the embryo.
Give the names few Pteridophtyes which shows heterosporous condition. Thus the chance of fertilizing an egg with the sperm of the same prothallus is very high. The permanent retention of the megaspore within the megasporangium has not become established. Though Selaginella as well as hetreospory Spermatophytes shows homologies in their structure as follows: One of the most important advantages of heterospory is the formation of seed habitat.
Temporary suspension of growth of embryo i. The formation of seed is one of the greatest evolutionary vents in the phylogeny of seed plants.
Thus, the endosporic development is a good starting hait for the survival of the young embryo. Retention and germination of megaspore within the megasporangium.
What are its significances? Reduction to a single functional megaspore per sporangium: The gametophytic generation is a weak link between the sporophyte and seed in the life cycle of heteorspory plants. This is made possible by the development of pollination mechanism. Development of seed dispersal mechanism. In Isoetes there are only megaspores in megasporangium. Among Pteridophytes, Selaginella rupestris is the most successful species that completed first four steps towards seed habit.
The condition of the production of two kinds of dissimilar spores, differing in shape and size in the same species, is termed Heterospory.
Heterospory and Seed Habit in Pteridophytes | Botany
This reduced the chance of genetic variability among homosporous plants. Heterospory is the production of two or more types of spores.
Leave a Reply Cancel reply Your email address will not be published. Development of organic connection between the megasporangial wall and the megaspores. Types of Stelar System and its Evolution in Pteridophytes. The origin of heterospory can be better discussed on the basis of evidences from paleobotany, developmental and experimental studies. In pteridophytes, further steps towards seed habit are lacking. Many spore mother cells disintegrate to form nutritive tissue.
The differentiation of microspores and megaspores and their dependence upon the sporophyte has certain advantages. In this article we will discuss about heterospory and seed habit in pteridophytes. Stelar Evolution in Pteridophytes. Jn chance of the survival of the independent gametophyte is very less. It has been suggested that heterospory arose due to degeneration of some spores in a few sporangia.
Heterospory and Seed Habit in Pteridophytes | Botany
Describe the advantages of seed habitat. Rounded red circles indicates different ni. Experimental studies on Selaginella Goebel, and Marsilea Shattuck, suggest that nutritional factors mainly govern the heterospory. In order to overcome this problem, the female gametophyte is permanently retained in the megasporangium. What are the advantages of heterosporous condition over homospory? The sporangia show greater specialization than those of ferns.
Such Peridophytes are known as homosporous and this phenomenon is known as homospory. No siphonogamy, therefore water is essential for fertilization.
Microspores are small sized spores produced in large numbers inside the microsporangium. In Marsilea 64 microspores and 64 megaspores are formed after meiosis in microsporangium and megasporangium respectively. Step 5, 6, 7, 8: During this period important heterosporous genera were Lepidocarpon, Lepidostrobus, Mazocarpon, Plaeuromeia, Sigillariostrobiis members of Lycopsid Calamocarpon, Calamostachys, Palaeostachys members of Sphenosida.
While in megasporangia most of the spore mother cells degenerate but in microsporangia only a few mother cells are disorganize. Formation of protective layers integuments around the megasporangium. They have identical organization but for their size. In the figure, Solid red circle indicates: Such Pteridophytes are known as heterosporous and the phenomenon is known as heterospory.