PDF | Summary The origin of the seed-plant life history, and subsequent should be considered two independent, fundamentally distinct evolutionary problems. Historical biogeography of the ancient lycophyte genus Selaginella: Early. Selaginella largely upon the basis of endosperm development, without regard to great diversities in habit and anatomical details. The association may be. The highest evolved species, i.e., S. apoda has advanced almost upto the In Selaginella, there is remarkable approach to the seed habit, on account of the.
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Related articles in Web of Science Google Scholar. Here’s how it works: In Selaginella erythropus megasporangium contains only one megaspore which is functional. The evolution of the seed is one of the major events in the history of land plants.
What is Vegetative Propagation? It thus forms better starting point for the new embryo, than an independent green prothallus which has to manufacture its own food. Sign In Forgot password? Sign In or Create an Account. Sign in via your Institution Sign in.
Don’t already have an Oxford Academic account? These are the basic requirements for seed habit: The sporangia show greater specialization than those of ferns. According to Rashid only 9 genera of Pteridophytes are heterosporous.
Heterospory and Seed habit in Selaginella | Plant Science 4 U
In Marsilea, Salvinia and Azolla the phenomenon of heterospory becomes distinct after meiosis. Close mobile search navigation Article navigation. The highest evolved species, i. General Characters of Pteridophytes Words. While in megasporangia most of the spore mother cells degenerate but in microsporangia only a few mother cells are disorganize.
The effect of a flower-dwelling predator on a specialized pollination system. If you originally registered with a username please use that to sign in. Each microsporangium contains a large number of microspores whereas each megasporangium contains usually only four megaspores. Leave a Reply Click here to cancel reply. In this article we will discuss about heterospory and seed habit in pteridophytes.
Advantages and Disadvantages of Vegetative Propagation. Abstract The evolution of the seed is one of the major events in the history of land plants. However, there are some Pteridophytes which produce two different types of spores differing in size, structure and function.
In Selaginella rupestris and S. Such Pteridophytes are known as heterosporous and the phenomenon is known as heterospory. The retention of megaspore permanently inside the megasporangium has not been well established. Most of the Pteridophytes produce one kind of similar spore. They have identical organization but for their size. The retention and germination of the fertilization of rvolution egg and embryo formation, which is still within germinating megaspore.
Meaning, General Characters and Affinities. Don’t have an account? Experimental studies on Selaginella Goebel, and Marsilea Shattuck, suggest that nutritional factors mainly govern the heterospory. From the above observations it is concluded that the life history of Selaginella approaches towards seed habit because of the following features:. Most users should sign in with their email address. Rather, we believe that the decisive character in this success is related to pollination.
In this paper, we consider the suite of characters that define the seed habit, and discuss the probable selective pressures that produced each character.
Importance of Heterospory and Seed Habit of Ferns (581 Words)
Development of an embryo sac within the sporangium. The condition of Heterospory in Selaginella constitute one of the most important phases in the hxbit of the plants.
Our major conclusion is that most characters are a direct consequence of the origin of heterospory and of natural selection for propagules with larger food reserves. The microsporangia contain microspores whereas megasporangia contain megaspores in them. Reduction to a single functional megaspore per sporangium: Here one thing may be noticed that the microspores develop male gametophytes whereas the megaspores the megaspores germinate into the female gametophytes which may also be called as microgametophytes and megagametophytes.
Newer Post Older Post Home. Selafinella Most Read Most Cited Does the shape of forelimb long bones co-vary with grasping behaviour in strepsirrhine primates? Though Selaginella as well as lower Spermatophytes shows homologies in their structure as follows: Such Peridophytes are known as homosporous and this phenomenon is known as homospory.
Heterospory and Seed Habit in Pteridophytes | Botany
This article is also available for rental through DeepDyve. During this period important heterosporous genera were Lepidocarpon, Lepidostrobus, Mazocarpon, Plaeuromeia, Sigillariostrobiis members of Lycopsid Calamocarpon, Calamostachys, Palaeostachys members of Sphenosida. According to Williamson and Scot two species of Calamostachys form the initial stage that might lead to the heterospory.
The origin of heterospory can be better discussed on the basis of evidences from paleobotany, developmental and experimental studies.