EVOLUTION OF SEED HABIT IN SELAGINELLA PDF

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.

Author: Dara Tygora
Country: Nepal
Language: English (Spanish)
Genre: Science
Published (Last): 5 March 2012
Pages: 40
PDF File Size: 17.21 Mb
ePub File Size: 15.48 Mb
ISBN: 489-1-59393-341-5
Downloads: 39315
Price: Free* [*Free Regsitration Required]
Uploader: Mezit

Answer Now and help others. In heterosporous Pteridophytes the development of micro and megasporangia follow the same pattern. These are the basic requirements for seed habit: Heterospory and Seed habit in Selaginella. Newer Post Older Post Home. 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.

Many spore mother cells disintegrate to form nutritive tissue. According to modern pteridologists the heterospory is found in seven genera-Selaginella, Isoetes, Marsilea, Salvinia, Azolla, Regnellidium and Pilularia. Gymnospermsheterosporyintegumentspollinationseed habit. However, some heterosporous pteridophytes possess integument-like structures.

Heterospory and Seed Habit in Pteridophytes | Botany

By sudden lowering of the temperature, the size of the microspores in the sporocarp of Marsilea increases by six times. Most users should sign in with their email address.

  1997 ACURA TL MANUAL PDF

In Selaginella Isoetes it is distinct before meiosis. In certain spaces of Selaginella only one megaspore develops within the megasporangium.

In Isoetes there are only megaspores in megasporangium. Citing articles via Web of Science According to Rashid only 9 genera of Pteridophytes are heterosporous. Structure of Rhynia With Diagram Pteridophytes.

You do not currently have access to this article. However, there are some Pteridophytes which produce two different types of spores differing gabit size, structure and function.

Retention and germination of megaspore within the megasporangium. They have identical organization but for their size. General Characters of Pteridophytes Words.

Development of protective layers and nutritive tissue around megasporangium. Development of an embryo sac within the sporangium. Megaspore is protected by its wall also but not by an integument. Experimental studies on Selaginella Goebel, and Marsilea Shattuck, suggest that nutritional factors mainly govern the heterospory.

Importance of Heterospory and Seed Habit of Ferns ( Words)

Sign in via your Institution Sign in. The condition of the production of two kinds of dissimilar spores, differing in shape and size in the same species, is termed Heterospory.

There is reduction to one megaspore in some species, e. You must be logged in to post a comment. Most of the Pteridophytes produce one kind of evoluion spore.

Evidence for a complex evolutionary history of mound building in the Australian nasute termites Nasutitermitinae. The condition of Heterospory in Selaginella constitute one of the most important phases in the evolution of the plants.

Among Pteridophytes, Selaginella rupestris is the one species that is very close to seed habit. Sign In or Create ij Account. In this paper, we consider the suite of characters that define the seed habit, and discuss the probable selective pressures that produced each character.

  APULEIO O ASNO DE OURO PDF

Similar type of abortion of spores was also observed in Stauropteris Chaloner, Lepidocarpon and Calamocarpon. Difference between Racemose and Cymose Inflorescence. According to Williamson and Scot two species of Calamostachys form the initial stage that might lead to the heterospory.

Reduction to a single functional megaspore per sporangium: Development of only one megaspore per megasporangium for example, in Selaginella monospora, S. It furthers the University’s objective of excellence in research, scholarship, and education by publishing worldwide. When one kind of spores are present, e. Such Peridophytes are known as homosporous and this phenomenon is known as homospory. These species were C. Here’s how it works: Such Pteridophytes are known as heterosporous and the phenomenon is known as heterospory.

If you originally registered with a username please use that to sign in. Microspores are smaller in size and develop into the male gametophyte while the megaspores are evolutiln and develop into female gametophyte. Types of Stelar System and its Evolution in Pteridophytes.